Carbon Monoxide Facts

by / Friday, 22 February 2013 / Published in Healthy Building Inspections & Testing
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Carbon Monoxide Facts

Are you concerned about possible Carbon Monoxide being present in your home or environment?

Below is a list that will help you stay safe.

Too often we get calls and hear misinderstandings about carbon monoxide (CO). Here are some carbon monoxide facts and common myths broken down.

Carbon Monoxide Myth

I can smell carbon monoxide when the furnace is on.


CO is actually colorless, tasteless, AND odorless. Because it cannot be noticed without a detector or meter, CO has earned the dubious name of “silent killer.” When folks call and say they can “smell carbon monoxide,” they are usually referring to other combustion byproducts that the human nose can detect. If you can smell combustion byproducts there is a problem that should be addressed ASAP.

Carbon Monoxide Facts - Where to install CO Alarm

Carbon Monoxide Facts – Where to install CO Alarm


Carbon monoxide is heavier than air, so CO detectors should not be placed on the ceiling or high on the wall.


CO is slightly lighter than air. However, studies have shown no significant difference in measurements based on what height CO detectors are mounted. Different manufacturers recommend different mounting locations, and you should always follow the manufacturers’ recommendation.

CO has a molar mass of 28.0, and air has an average molar mass of 28.8. The difference is so slight that CO is found to evenly distribute itself indoors. It is worth mentioning that CO indoors is usually generated from incomplete combustion (heat source) and therefore traveling in a warm air stream. Warm air is more buoyant and does rise. Coupling this fact with the knowledge that CO is lighter than air…  I personally have my CO detector located on the ceilings.

Carbon Monoxide Facts

CO Facts – New Rules for CO Alarms

Placing the alarm in a high area of the home, where smoke and hot air would collect during a fire, seems like the most logical advice for me. I have heard that air can stagnate in some corners, so it’s advised not to install a smoke or CO alarm within 16″ of the side wall or ceiling. In other words, if you’re going to install it in a hallway, put it in the center of the hallway ceiling – not too close to a side wall.


Our CO Detector Recommendation:  *Healthy Building Science recommends the
First Alert CO605 Carbon Monoxide Plug-In Alarm with Battery Backup.
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The National Fire Protection Association says CO detectors “shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms.” Additionally, each CO detector “shall be located on the wall, ceiling or other location as specified in the installation instructions….”

The International Code Council (section R315.1) pretty much mirrors the above language. “For new construction, an approved carbon monoxide alarm shall be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms in dwelling units within which fuel-fired appliances are installed and in dwelling units that have attached garages.” If there are no combustion appliances, then CO detectors are not required by this code.

California Senate Bill 183 requires CO alarms for any dwelling unit with a fuel burning appliance, fireplace or attached garage. This accounts for the vast majority of residential buildings in CA. Effective in 2011 all new and existing single-family construction must install CO alarms, and in 2013 all multi-family dwelling units were required to be outfitted with CO alarms.

LEED-H requires CO alarms and offers points for outfitting garages with a minimum 100 cfm exhaust fan, per bay, in order to reduce the risk fo CO poisoning. The exhaust fan should run continuously (energy hog) or may be connected to the garage door opener, motion detector, or CO sensor.

Carbon Monoxide Facts - CO Kills

Carbon Monoxide Facts – CO Kills


Carbon monoxide is not dangerous.


CO poisoning is the most common type of fatal indoor air poisoning in countries where cooking and heating is still dominated by fires. More than 500 Americans die each year from unintentional carbon monoxide poisoning.

Symptoms of mildly acute CO poisoning include lightheadedness, nausea  headaches, fatigue, and flu-like symptoms. Acute CO poisoning leads to sleep and the failure of the central nervous system and heart – leading eventually to death during sleep. The following chart from Wiki summarizes known human symptoms associated with different levels of CO exposure. If we detect ANY CO indoors, we consider it an immediate action.

CO Health Effects - Wiki Chart

CO Health Effects – Wiki Chart



Carbon monoxide poisoning is like any other kind of poisoning.


CO bonds to hemoglobin (Hb), and instead of carrying oxygen (O2) the hemoglobin is then occupied with CO – creating carboxyhemoglobin (HbCO). CO poisoning is actually the result of the head and heart not receiving sufficient oxygen… or asphyxiation.

If a person is removed from a high-CO environment after acute CO poisoning they may still suffer difficulty with some mental functioning such as short-term memory, dementia, amnesia, irratibility, an unusual walking gait, speech impairments, and depression. I’ve spoken with people that said it’s taken them months to fully recover their mental functioning after an acute exposure event to carbon monoxide.


Carbon Monoxide Facts

CO Alarms Need Replacing or Calibrating


Carbon monoxide detectors are in perfect working order if they beep when I push the test button.


Gas sensors in CO alarms have a limited lifespan, generally less than 6 years. The test button on common CO alarms only tests the battery, not the CO gas censor. It is recommended that CO gas sensors be periodically tested and calibrated by exposing them to a known amount of CO. Because CO alarms have come down so much in price, it’s generally cheaper to replace the alarms than have them calibrated.

Most CO alarms sold today in the US will not sound an alarm until concentrations greater than 50-70 parts per million (ppm) are reached. Many believe CO alarms should signal at far lower levels. In fact, the Building Biology guideline is that indoor CO should never exceed outdoor concentrations. Where we live, in the San Francisco Bay Area, it is rare to detect more than 1 ppm in outdoor air unless you are standing near an active flue or chimney.


Carbon Monoxide Facts

CO Facts – CO comes from incomplete combustion


The most significant source of human-produced CO is formed during combustion when there is insufficient oxygen (O2) to product carbon dioxide (CO2). Imagine where this scenario may take place… does a hot water closet come to mind? How about a furnace located in a crawlspace or attic? Or a poorly vented kitchen with a gas stove?

Installing a CO alarm is a low-cost way of significantly reducing your risk of CO poisoning. Do it. It’s inexpensive and easy. Replace the batteries according to the manufacturers instructions, and replace units at least every 5 years. 

Carbon Monoxide facts should be well known to everyone. Hopefully these tips will help you reduce risk of CO poisoning.

Testing for Carbon Monoxide is a standard part of our Healthy Building Inspections.


Do You Need Help Or Have Questions?  Contact Us Below.

Carbon Monoxide Facts - I smell CO

Carbon Monoxide Facts – I smell CO


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85 Responses to “Carbon Monoxide Facts”

  1. Alex Stadtner says :

    There are thousands of buildings with gas ranges and no mechanical ventilation. You’ve got the right idea. It would be best to a) have a CO detector installed and operational and b) open the windows and doors to ensure adequate insulation and reduce the risk of CO poisoning. Cook safe!

  2. Paul says :

    Just installed a gas range and the family wants to use it before the exhaust vent is finished. Can the oven be used if the windows are open for cross breezes?

  3. Alex Stadtner says :

    Not sure what sort of symptoms you’re talking about. If you’re concerned about CO you should all vacate the building immediately. If someone is passing out or unconscious and you suspect carbon monoxide poisoning you should remove them from the space immediately. Get a CO detector or meter ASAP. It is possible for some people to be more susceptible to various environmental contaminants and symptoms. But CO can kill even the healthiest and strongest among us.

  4. Dusty says :

    Im wondering. if 1 person is symptomatic, will others in the household be as well? Or is it possible for 1 person not to have symptoms at all, while others do?

  5. Alex Stadtner says :

    Suggest you contact a local industrial hygienist who can perform a professional indoor air quality survey.

  6. Barry freeman says :

    I am aware of that slight burning sensation with a slight thick head and taste , like when the gas of a cylinder heater bottle has just emptied ,we have one but we havent used it for months ,we have no mains gas appliances either
    Any ideas please both our neighbours have them and we are in a terrace with shared roofspace could we be be drawing fumes in somehow ?

  7. Alex Stadtner says :

    I would respectfully disagree with your husband on this one. If you have ANY combustion appliances indoors, including an attached garage or gas fired furnace or stove/oven, it would be wise to have a CO detector. They’re relatively inexpensive and could save your lives. The cost-benefit ratio makes it a no-brainer, but don’t ever tell your husband I said that! Good luck and stay safe.

  8. Deborah P Simonson says :

    Hi, my husband is saying we don’t need a C O Detector, because we only use propane to heat and cook with, our hot water heater is outside. And he says because we live in a old modular home that is not air tight, it could never build up enough C O to hurt us. I’m not so sure this is all true.

  9. Alex Stadtner says :

    Carbon monoxide is an odorless gas. Other combustion byproducts do have odors, some of which may seem “sweet,” so don’t ignore mystery odors indoors. The sweet smell is not CO, but may be a chemical cocktail which includes CO.

  10. tt says :

    To the person smelling the “sweet” smell. This very well CAN be carbon monoxide. We had a sweet chemical smell in our house. It seemed to happen a lot when it rained or got cold. Our furnace guy seen nothing wrong with our furnace, but our neighbors furnace kicked on while he was there. It’s a bad heat exchange most likely, and will put carbon monoxide into the home. We have told our neighbor the issue, asked her to fix it, seeing as I have small children in home, and she refuses to fix it. Every time it rains or gets cold, I have to get my kids out of our house and find somewhere to go, because gas co will not shut her gas off since it’s winter and she’s older… no mind to my kids at all though. So, have heat exchange checked.

  11. […] monoxide is the leading cause of death by poisoning in the United States. In fact, each year over 500 people die in the U.S. due to unintentional carbon monoxide poisoning. Because this substance can quickly cause a person […]

  12. Alex Stadtner says :

    Propane and the odorous additive are different than CO. They’re all “gases,” but they’re all different.

  13. Denny Johnson says :

    Since propane has a odor is a leak in a propane furnace considered carbon monoxide? What is the difference or is there one?

  14. David Sasse says :

    I do not think CO leaches into food. Also, CO is not really toxic, it is an asphyxiant, it replaces oxygen in your blood and virtually suffocates you, so it is only really dangerous at higher ppm levels (50 ppm and above).

  15. Tara says :

    Can CO leach into food? Eg: if I cooked food in a gas oven which was producing CO would the food “absorb” the gas. And if this was possible what would happen if you ate the ‘tainted’ food?

  16. […] Click here for more information and links regarding carbon monoxide! […]

  17. Alex Stadtner says :

    Mystery. There could be an outdoor source. The change in temperature could trigger it? A chirp is likely when the battery is low. Perhaps the action of closing the door joggles the wires or battery so it chirps? Get a second detector or check the batteries. Don’t ignore it or unplug it. Good luck.

  18. Donna says :

    Every time I go outside & come back in I walk past our carbon monoxide detector & it chirps, what is causing this

  19. Alex Stadtner says :

    CO is odorless. So if it’s a sweet smell you are probably contending with another gas. If you’re suffering nausea and dizziness I would consider that urgent. Get an industrial hygienist or Building Biologist out there right away. Open windows and increase ventilation in the meantime. Be safe. Those are serious symptoms usually associated with an acute exposure.

  20. Emma douglas says :

    I smell a sweet smell when I go to bed have for /days been nausea n dizzy was concerned if it was carbon monoxide I don’t have a detecter but what I’ve read it has no smell been 2days of the nausea n dizziness

  21. Emma douglas says :

    I’ve been smelling a sweet smell when I go to bed. The last 2 days I’ve been nausea n lightheaded I do not have a CArbon monaxide meter installed but I read there is no smell to carbon monoxide gas so hoping it is the flu no headaches after reading this I wonder if I’m safe?

  22. Alex Stadtner says :

    Great comment on the potential for false positives with a CO detector. Thank you.

  23. John says :

    Your readers should note that many Carbon monoxide detectors will detect the presence of gas (natural, or propane), so a leaking appliance or delayed ignition could sometimes be a cause of the alarm going off if no Carbon Monoxide is found.

  24. Jose Bejaranoo says :

    My gas stove burner was lighting up so I tried to force knob back and forth a couple of tries then my wife and I decided not to play with it. So 10 minutes past and then the CO alarm went off so I quickly got a pillow and started to air the alarm thus we opened all Windows for the rest of the evening. In matter of minutes the alarm went off on its own. I started getting dizzy and light headed around all this was happening. Should i be scared of long term damage done by the CO but I can’t explain how so much CO will activate the alarm if i was just playing with the knob for less than a minute.

  25. Alex Stadtner says :

    Wow. Sounds like a close call. You should probably get a secondary CO alarm and install it in your bedroom so you certainly hear it next time. As long as the repair is complete and the CO alarm(s) isn’t going off any more, than I would assume it is safe. But without testing the building we cannot say for sure. Get a secondary CO alarm for the bedroom and that should help you sleep better at night. Close call. Some folks don’t wake up after incidents like that. Be grateful and play safe.

  26. Anita Conley says :

    Hi Alex
    I was sleeping and my husband was getting ready for work and i could hear what i thought was a smoke detector going off, it was really our carbon monoxide detector. I got out of bed because the bedroom smelled and the whole house smelled. My husband said he heard a bang from our basement and the entire basement was filled with smoke. I called our landlord who called our furnace guy and we opened all the windows. The furnace guy came and said that a pipe had disconnected in our furnace and that our house was filling up with carbon monoxide. The detector is off now but it was scary. Do you think its still safe to be in the house?

  27. Alex Stadtner says :

    Thank you, Dr Michael Brunson.
    We appreciate your feedback and serious approach to CO poisoning.
    It’s no joke.
    Thanks for writing in,

  28. Dr. Michael Brunson says :

    Dear Alex, I just wanted to send you a brief note and mainly say how much I appreciate your information and advice. As a clinical psychologist, I’ve done my share of neuropsychological testing and evaluations, and CO is both a killer and a source of serious brain damage and dementia. My understanding is that even low level exposure over time can cause relatively permanent cognitive and other brain injuries. As you note, CO IS COMPLETELY ODORLESS, and good CO detectors that are in proper working order are critical for our safety. Again, thank you so much for your understandable and helpful information. Respectfully, Dr. Michael Brunson

  29. Alex Stadtner says :

    In theory burning fires do create considerable CO2, but in an open-air setting I haven’t seen fires be a significant immediate problem for humans. I would suspect that the carbon dioxide would be so diffuse that it wouldn’t be that significant indoors. I think you may be thinking about carbon Monoxide (CO), and not CO2. The smell from smoke is an obvious indicator of poor air quality. Any new window screens? Or recent construction or pest control projects?

  30. Grant Parker says :

    I was wondering if it would be possible to have CO2 issues from open burning on days and nights where there is no breeze. I live in a neighborhood where this takes place 24/7 and yesterday morning I opened my windows very early and something came. It was not outright ‘smoke’ smelling though it reminded me of car exhaust but I could not put my finger on it. I have had an issue with the venting on my gas water heater a couple of years ago and this seemed to be the same but it was coming from outside in stalled air. When the sun came up and when the air started heating and moving it appeared to vanish outside, but it took hours to get it out of the house. My previous CO2 detector died a while back and I ordered a new one yesterday. This morning a faint smell of smoke but not that gaseous stench. There is no nearby garage or area where cars or trucks would or could be running for any length of time either. I am somewhat puzzled. Your comments would be appreciated. Thank you.

  31. Jay Worrall says :

    I have been told that our dual attic furnaces need to be replaced because of incomplete combustion. According to the service tech one recorded 1 ppm while the other recorded 3 ppm CO. Obviously these numbers are quite low compared to what is considered dangerous, but she said the CO could “pool.” Hmm. Searching the web I have not found a lot about how such a test should occur–1 ppm or 3 ppm over how long? Is any emission bad or is this just trivial, and an excuse to try to sell us a new furnace?

  32. Alex Stadtner says :

    An alarm is there to alarm you. So if it’s going off… you should be somewhat alarmed. Try replacing the batteries. If that doesn’t stop it perhaps you should replace it. If a second alarm sounded then you’d really know you had a problem. In the interim you could open more windows. Sometimes these units fail or their sensors get dirty and give false alarms. But I would not ignore it. Good luck.

  33. Jennifer Lynn says :

    My fire/CO alarm combination just started randomly going off this afternoon. It has 2 different alarms, 3 beeps means it’s fire and 4 beeps means it’s CO. It started going off today as the fire alarm, with 3 beeps, however, my house wasn’t on fire. I don’t have any gas appliance such as water heater, dryer, stove top. I’m not sure what else causes the alarms to sound Since my house wasn’t on fire but the alarm sounded should I be worried about CO anyways?

  34. Alex Stadtner says :

    Independent of your apartment there are no combustion gas appliances in the building (stoves, boilers, heaters, dryers, etc.)?

    It’s unusual for cars to trip CO alarms in larger open spaces. In a closed garage, sure. In an open garage 25 feet away from your window, unlikely.

    I would suspect that either you’ve got a faulty CO detector or there’s another source of CO interior to the envelope of the building.

    Don’t ignore it. If a second CO alarm goes off you’ve got a serious issue that deserves immediate attention.

  35. Derek says :

    I live in an 3rd floor apartment with no gas or wood burning and cars park 25+ feet away. Why would my CO detector be alarming with a new set of batteries?

  36. Alex Stadtner says :

    Call you local building health inspector. It’s probably for your city our county. If you’re a renter without a lot of money to hire an industrial hygienist and attorney, getting the city or county health inspector is probably your best bet. Good luck. You and your child shouldn’t have to smell combustion byproducts where you sleep. That’s unacceptable. Make sure you’ve got CO alarms and if they go off – evacuate yourself and your family. Move if it takes too long for the city/county to respond. It’s not worth the risk of carbon monoxide poisoning.

  37. Alex Stadtner says :

    It is possible that combustion exhaust from outside is sucked back into a building, but it’s rare that it would be in sufficient concentrations to trip a CO alarm. We’ve seen that occur where there’s a large indoor parking garage, but new codes require mechanical ventilation fixes to ensure CO doesn’t enter the building in high concentrations. So… I suppose it could happen. But more likely you’ve got a leaky flu somewhere that is otherwise affected by the pressure differential you’ve been tinkering with by opening and closing your windows. Good mystery. Thanks for sharing. Please let us know if you figure it out.

  38. Linda says :

    I need some advice/help. The apartment unit I am located in is directly next to our building’s flue. Every time I am on our patio I can smell combustion byproducts, constantly, everyday. I had the gas company come out and they did detect CO with their sniffer, and they even gave me a red slip for the owner. It took several months, but I finally got the building manager to extend the flue, so that it’d be farther away from my unit. They only extended it by a few feet, and it didn’t really have an effect, as I continue to smell it everyday. I have 3 operable windows in my unit, that I Never open due to the smell, and even when those windows are closed, I can smell the byproducts inside. I believe my family is suffering from acute CO poisoning, and I’d like to know who I can contact about this issue in the Los Angeles area. Supposedly, the boiler is working fine, and the flue is up to code, so the building owner doesn’t feel obligated to address this issue, but I cannot believe that it is legal for my husband, young children and I to persistently get poisoned. I just had our manager seal our windows with caulking, but I honestly don’t know if that will make a difference. I am most worried about my four year old who just started to sleep by herself, because I could smell the combustion byproducts in her room at night while I’d go check on her. What should I do?!

  39. Tom Peterson says :

    It is summertime and warm outside so I open all my windows.
    My Carbon Monoxide alarms went off for the second time in a week. It doe not make sense because the only appliance that burns is a Navies instant on hot water heater which does not burn until hot water is called and none had been used for six hours or more. So I did the stupid thing and went inside and removed the alarms .

    The alarm that went off both times is the alarm at the bottom of the first floor stairs in the family room. The first time it happened I replaced the alarms and retested and they remained silent. Today after I removed that one alarm, the alarm at the top of the stairs went off and, because I need a step ladder to reach it, I removed that one as well. The cellar alarm where the water heater is located did not go off. The other reason I was not afraid to remove the alarms is because every single window upstairs and down were open. Beautiful day. So there is plenty of ocean air moving through. So I looked for commonalities of both occasions.

    Warm days not very humid. Otherwise I keep the house closed up and have the Daikin system dry the air. Never an alarm when house is closed up. The only other time I got an alarm is when the gas grill on the west porch was sending in smoke and I got the fire alarm- so closed the windows as smoke was coming though those opened windows. (Grill is not against house and is away from the house near the railing.) The west side of the house is about Nine (9′) feet away from my neighbors house. The homes are separate. The homes are two stories high and my house has a porch so the roof overhangs. The neighbor has two gas exhaust pipes coming out from his house about midway down the wind tunnel. My hot water exhausts near the from of my house in this same tunnel and is new this winter. Today I am looking at a flag and see it is fluttering toward the open windows in my house located in that tunnel.

    My question: is it possible the exhaust entering the outside from both houses is being blown back into the very room where the alarm is going off? I tend to think that is the case and the prevailing winds typically blow in this direction. It only makes sense to me that this only happens when windows are open. I called my plumber and he mentioned to close windows on that side of house. I vacuumed off alarms that sounded, replaced them and tested. Then, I walked around to close all the windows in the house and you can imagine I felt really stupid doing that! That was about 1.5 hours ago. I put the air on as it is hot and not a sound.

    I am going to call the HVAC installer and have him come and test and if he finds nothing I suppose this will be the fall guy. If they find nothing, is there any way to remedy this? The exhaust pipe is three feet above ground, windows are opened west and east so air would be pulled in from where exhaust pipes are located. Would moving/running the exhaust pipe up the side of the roof remedy this situation? I do love to open the windows.

  40. […] idea, it does look like they have a limited life span, 6 years, even if the button works, here link. So after 5 years I'd stick it right to the exhaust and test it that way. They also say placement […]

  41. Alan says :

    I the previous modern home we had, the kids were constantly sick and got worst in the Winter: whooping cough, vomit, fever etc.. I found out the central humidifier water was thick and smelly, it looked almost like yogurt. Was it the cause? So I took it off, turned off the humidifier water line but the kids still got sick and asthma. We moved to another house older but it had gaps in walls and I always had a window in the basement and a top floor window opened a little for air flow ( the house was actually drier and warmer in the Winter) the kids had not sick since and no more asthma. My conclusion is, all the newly built homes with air tight to conserve energy, they are sick trap, they make people sick with dirty air (cleaning detergents, gas cooking, floor gas etc..)

  42. Alex Stadtner says :

    Sure. Buy a mask. But it won’t do anything to prevent asphyxiation from carbon monoxide poisoning. You shouldn’t have CO indoors. (period)

    So the easiest safety measure is to purchase a CO detector and perhaps a meter. When/if you detect CO you know you’ve got a leaky flu or other incomplete combustion occurring within the building. First get out and ventilate the space until well after the detector goes back to sleep. Have pros find and fix the problem. Do not hangout in the building if a CO alarm is sounding off. A mask will not “filter out” CO or protect you from CO poisoning.

  43. ella derling says :

    Should I buy masks? I’d like to be careful but don’t know where to start…

  44. Alex Stadtner says :

    Yes. What you’ve explained is possible and has happened before.
    Carefully locating outside air intakes is important, as are non-idling policies.

  45. Becky says :

    I am a Stationary Engineer at a University. Is it possible to get CO accumulated from brief episodes of exposure throughout the day and from external sources as vehicles running in close proximity to your central heating and ac unit intake that is directed to an enclosed office/control room. Maybe even a boiler stack if the conditions are right (cold dense air)…just curios…thank you.

  46. Alex Stadtner says :

    Glad you’re okay. Carbon monoxide poisoning is no joke, and it can lead to death in extreme circumstances.

  47. Barbara says :

    Thank you for the article. I do not have a question but would like to tell my story as a warning to others. I had exposure to low levels of carbon monoxide from approximately 1977 – 1980. It was years before I discovered it was carbon monoxide. I kept having flu like symptoms, fatigue and just kept getting sicker and sicker but it was always worse in the winter. What I eventually discovered and only after renovations that replaced an old brick and mortar chimney was that there were holes in the mortar in many places and in particular very near the light switch in my bedroom. The old house originally had a coal and wood furnace which was replaced by a gas furnace but it did not have a steel liner installed. The gases from the combustion of the natural gas broke down the mortar causing the holes allowing for the carbon monoxide to leak into the rooms of the home. It took me years to recover since my health had deteriorated significantly. In later years, even when the CO detectors became available, they did not I register at low enough readings for my situation. I did replace the old gas furnace with a mid efficiency furnace (1980ish) inside a furnace room with venting to the outside. Why a steel liner was not installed when the 1st gas furnace was installed, I do not know.

  48. Alex Stadtner says :

    Hello Marci,

    What a case! I’m glad you’re concerned and I’m very glad you’ve got those CO alarms. This is exactly what they’re for.

    1) It is entirely possible that the oven/stove are significant sources of indoor carbon monoxide (CO). We’ve measured ovens that quickly raised indoor CO off the charts. Other possible sources are boilers, water heaters, pool/spa heaters, and any other combustion appliance within the envelope of your building. All combustion appliances should probably be checked out. Sounds like you’ve cleared the furnace.

    2) All combustion devices should be properly exhausted. If there are blockages (physical) or back-flow (pressure) issues – they must be identified and addressed. Not sure why the basement CO alarm would go off and not the kitchen/indoor CO alarm… But it may involve how the oven/stove are vented. All the exhaust vents should be inspected and tested.

    3) For the pressurization issues you might need to find a Home Performance Contractor or Building Biologist. These folks are trained at assessing CO and may have a more holistic approach to assessing your building.

    4) CO alarms have been known to be faulty. If the basement alarm keeps going off… you might switch it out with another alarm elsewhere in your home. If it keeps going off in the basement – you’ve likely got an issue. If the old basement alarm keeps going off in the new location – you’ve likely got a faulty alarm.

    Them’s my thoughts for the moment. Good luck!

  49. Marci says :

    Hi Alex,
    In December, our CO detectors in the basement and garage (located on the same level) started going off, then the others started going off on first floor. I was out out that night but my husband got the kids out of the house, called 911 and they found unsafe levels in our home. We had the oil-fired furnace serviced the next day (even though it had been cleaned a few months prior, they suspected a dirty filter was the cause…). Three weeks ago, they started going off again in the basement. We opened the slider door, the detector went back to 0 and the HVAC guys suspected it was because the exhaust fumes could be coming back into the house, so he sealed that up extra tight.
    Yesterday morning, they went off again…Clearly scared about this issue, I called my HVAC guy PLUS a second HVAC company, so they could brainstorm together. They both concluded the furnace (a 2-year old Boderus) was running perfectly after extensively looking it over, testing it, etc. They checked everything else out and both guys were stumped. So, I called the propane company that services our house and had them come over too (we have propane for our fireplace and stove). He also concluded the furnace and other systems were totally fine. He had his device that reads levels and he checked everything but when he got to our gas stove and turned on the oven, his device started going up and up, showing it was giving off carbon monoxide. He disconnected the stove and determined that was the cause. Still not convinced, today I had two more HVAC guys come out together and they ALSO concluded the furnace, etc. were all fine. They also used their device and when they tested the stove (they had hooked it back up to test it), it again started giving off carbon monoxide very quickly (within a couple minutes). In addition to a faulty stove, they also determined that the regulator pressure was at 9.5 but is supposed to be set from 11-14 per the stove manufacturers recommendations which they said would be adding to the problem. I purchased a new stove this evening BUT my question for you is, can this really be the source of our issues??? This is causing me a lot of anxiety, as you can imagine, and I need to be sure we have found the culprit. The stove is on the first floor, so why would the detectors in the basement be going off…? They didn’t go off the night we used the oven, but rather the next morning. There is a return vent (for our a/c unit) a few feet from the stove…does this add up to you? Why did the basement ones go off before the ones on the same level as the stove? Could there be a problem with pressurization or ventilation in our house…? These are things I am not too familiar with but read about online. I would LOVE any thoughts you have!!!
    Thank you!

  50. Alex Stadtner says :

    It would completely depend on your meter and how it’s set up. Zero is the most common finding on CO meters… because there shouldn’t be any detectable carbon monoxide in occupied areas. It’s unclear whether your meter’s “max reading” is historic or from the point you turned it on. If there was an active range between 0-41ppm, I would assume that any half-way decent meter would show some variation. It may be worth getting a second meter or renting one from a friend just to double check. CO should only be produced when there is combustion occurring. There may be a very small amount generated from a pilot light, but when the real concern would be when the furnace is actively fired up and running. Same with water heaters and boilers. It’s the combustion process that generates the CO.

  51. Matt says :

    2 questions

    1. My CO detector says 0, but when I hit the button that says max reading, it says 41. So not constant. Is that bad and should I be concerned?

    2. Can CO from a furnace be an issue at all if the furnace is off or not running? In other words, is CO produced if the furnace is off?

    Thanks for your time!

  52. Ronald says :

    I live in a room, can carbon monoxide be in a room?

  53. Chloe says :

    I have one in my hall way my hallway is were the heater is and it heats up the hall very fast but not the rooms my Ceiling is very low I’m five four and I can touch it last yr my alarm didn’t go off but this yr it’s like every other day I have a small space heater gas my hall is L shape with the heater in the corner I have the alarm on the wall on the same side on the small part of the L because that’s were the kids bedroom are at If I move the alarm living room it stops going off or in the kids room if doesn’t go off is it do to my location?

  54. […] Carbon Monoxide Facts and Myths. What You Need to Know About CO […]

  55. Sophia says :

    Yes. Your location sounds suitable based on the limited information available. Good to locate it away from a large fan or opening that allows for ventilation.

    How do you know that your 42 year old CO detectors are still functioning as intended? I would suggest testing them with CO or replacing a carbon monoxide detector that old. A lot has changed in monitoring and metering technology in the past 4 decades. Stay safe.

  56. Clyde Reed says :

    Replacing batteries in smoke alarms and CO alarm, and ordering replacements for any expired alarm. Our HVAC furnace is in the attic, and attic is closed by a close-fitting panel which drops into the attic access frame. But six feet away is a whole house fan with shutters located in the hall ceiling, which have shutters which are not airtight when the fan is off. Additionally, just had a new roof installed, and per code I needed nine roof vents, which I had increased to ten. I have the current combination smoke/CO detector on the wall at the end of the hall near the shutters. Is this location OK? In the short hall, the only other spot would be between the attic access and the shutters.

    FYI: As soon as CO detectors were available I purchased a plug-in (the only ones available then). Been here 42 years and still functioning!

  57. Richard says :

    A great portable CO detector is cut flowers. They will wilt quickly in the presence of CO. A good friend of mine was feeling poorly and having headaches. She noticed that flowers delivered for a party had wilted overnight. She called her husband who is a doctor and he told her to get out of the house ASAP and he would send an ambulance. It turned out that a boiler flue for a swimming pool had been inadvertently closed. It had affected her more than him because she had been home a lot preparing for the party.

  58. Alex Stadtner says :

    I’d suggest you call your local gas utility to use a gas-sniffer to see if there are still combustible gases around your building. They usually do this for free.
    If you were suffering dizziness or nausea from inhaling natural gas – you’d be in real trouble. Call a doctor or 911 if you have any doubt. If you think you have a gas leak you should get help immediately. It is a fire and explosion risk.

  59. Joey says :

    I sealed the valve on the gas line after it broke, I’m waiting to get the part when the place opens. Is it ok of I use the microwavem It’s been 5 hours and I have no dizziness or naseu.

  60. Alex Stadtner says :

    Yeah. You’re probably fine. To really determine the risk you’d need to know the CO emission rate of the generator, volume of the space, and any influences to outside ventilation (e.g., how much the door was open, wind, forced air, etc.). But as long as nobody is suffering symptoms of carbon monoxide poisoning you’re over the point of concern.

    I know that feeling… of realizing you’ve made a mistake after the fact and wondering what damage may have been caused. Based on what you’ve shared I wouldn’t worry too much about it.

    Best of luck, and be safe with that generator!

  61. Thomas says :

    Hey, was in a large warehouse when we lost power to the building completely. Had to run a generator for about 25 seconds to close an over head door. We ran it inside because it’s a larger warehouse and didn’t want to leave the generator outside. We were exposed to generator fumes for about 1 minute total without going outside…its been about 5 hours now and all is wel. Just wanted to ask a professional if we should be concerned about anything…didn’t think about it till after the fact.

  62. Alex Stadtner says :

    Hi Stacey,
    I’m afraid I cannot help with the medical questions you have posed, but we can say that the description of the room you provided does raise some concerns. Carbon monoxide (CO) poisoning symptoms should subside with time when you’re away from excessive levels of CO. And don’t rule out other potential contaminants and pathogens in the space. Your symptoms may also coincide with exposure to some species of toxigenic molds. I would suggest that you continue your medical evaluation and working with your doctors while you also begin to more intentionally evaluate your home for environmental contaminants. Get a healthy building inspection from a trusted local industrial hygienist.
    Best of luck, and please let us know what you learn,

  63. Stacey says :

    Hello Alex, my family and I are getting concerned over my decline in my health over the past year. I work in a commercial setting where I use gas appliances and the only “fresh air” into the room is a hole in the wall of which the parking garage butts up to. I have , within the last year, been diagnosed with benign vertigo (extreme dizziness and nausea ) by my doctor. Along with the vertigo, headaches, weight loss, heightened irritability and fatigue are some of my main concerns. I’ve tried to just “get by”, I’m worried about losing my job and my employer just shutting down this department if I show concern. But now my husband and family are really very scared about the excelleration in my declining health.
    My doctor told me about a test that is performed in the hospital that measures the amount of CO I have in my blood. He doesn’t want to put me through that if at all possible but I’m not sure at this point what my other options are? After your link was forwarded to me from a family friend and Doctor, I thought you would be a good source for help.
    Thank you for any advice you can provide me with, Stacey

  64. Alex Stadtner says :

    Yeah. You might be on to something with poor combustion. Could be internal to the furnace (air mixing, dirty burners, etc.), or could be more to do with insufficient supply air (ventilation to basement). Interesting case. Glad the chirping has subsided and wish you the best of luck.

  65. Alex, Thank you for your reply to my e-mail on the 19th of May. Your help is greatly appreciated.

    I’ve been extremely busy at work and with family matters and have not been able to fully investigate the issue (such as monitoring the basement for Radon gas). I have kept the small basement window open since our e-mail correspondence, to provide natural ventilation to the enclosed basement room, and since then the CO detector has never chirped. Not even once. I did NOT change the batteries are in the detector so the battery issue appears to have been eliminated.

    Last week my wife called me at work to let me know she had no hot water in the shower. When I got home that evening I found that the furnace (only used to supply hot water during this season) was not starting. I hit the restart button. The furnace started and has been functioning well since but perhaps that points to a poor combustion issue.

    In any case, this is still strange to me …because the chirp sequence I was hearing (before I left the window open) was a low battery type alarm and not a CO type alarm according to First Alert.

    I will let you know more when I get a chance to do more investigation.

    Thank you.

  66. Alex Stadtner says :

    Hi Michael,
    Interesting mystery and good set of facts / clues to work from. I’ve only heard the Carbon Monoxide detectors chirp when they are low on batteries. The detectors are generally only designed to make noise if they 1) detect carbon monoxide over a set level, and 2) if they are low on batteries. And the sounds and frequency of chirps are different for each scenario. I might try changing all the batteries again, but it’s totally strange that the other meter experienced the same effect and “they symptoms” disappeared when removed from the furnace closet. But having listened to too many geiger counters … you’re also correct that ionizing radiation (electromagnetic fields / “EMF”) could be interfering somehow with how the device is scanning it’s battery level. I haven’t heard of this before… but it’s possible. You can pick up a rather inexpensive DIY radon test kit at a local hardware store and see if it’s unusually high. That would be an indicator. And to see if your household electrical system is somehow involved you could turn off power at your main electrical panel and see if the chirp continues. Please let us know what happens. We get odd-ball mysteries like this and we keep learning by folks like you sharing their stories.
    Don’t ignore it. If your CO detectors are faulty or keep tripping… pay attention and do get to the bottom of things. Don’t want to take that long nap.
    Best of luck,

  67. Michael Donati says :

    I have a First Alert battery powered CO detector (made in 2013) in my basement furnace (home heating oil) room which is enclosed with doors. We began noticing a intermittent chirp in our home over the last couple of days. Last night I tracked the chirp noise to the CO detector in the furnace room. I confirmed that the voltage was low on the two AA batteries, replaced them, and vented the room to be safe. This morning the same intermittent chirp could be heard with new batteries in the unit. I took the unit out of the furnace room and the intermittent chirp appeared to go way. I then took a another CO detector (First Alert CO606 I installed in December 2015) which is normally mounted in an electrical outlet in the basement (outside the furnace room) into the furnace room and it began producing the same intermittent chirp noise. I called First Alert and the representative told me the noise I was hearing indicates low battery, and the units might have to be cleared, but that does not make sense to me especially since the CO606 was running off the electrical circuit and functioned normally as soon as removed from it from the furnace room. I had my local fire department come (non-emergency call). They did NOT detect CO in the furnace room with their hand held unit but the Fire Chief had trouble turning his had held unit off in the furnace room. Very Weird! Could the issue be some type of EMF radiation or even Radon (we live in New Hampshire) causing the CO detectors to malfunction when in the enclosed furnace room? I’m stumped. Your help will be greatly appreciated. Thank you.

  68. Alex Stadtner says :

    Wow. That was a close call.
    Think of how many people are suffering milder symptoms in the country, and they are completely unaware it’s associated with their indoor air quality.
    You are lucky. Dizzy and nauseous mean you were slowly being suffocated. Thank goodness you figured it out. When a company sells a CO Detector it should have an option to alert occupants if even 1ppm is discovered. Any measurable Carbon Monoxide – especially above 5 ppm – is indicative of a problem.
    I’m sorry you had to learn the hard way.
    Thanks for sharing your “sick building” story,
    -Healthy Building Science

  69. Lia Trocano says :

    I had a close call from a “Mr. Heater” propane heater which claims to have an alarm so I didn’t worry. When I got terribly dizzy, nauseous and had a headache my daughter showed up with a meter. So what I’ve learned is that an alarm is pretty much useless for long term exposure. Using the meter I’ve been able to pin point two sources of CO. The heater that I no longer use and the not vented propane stove. It’s been 3 months and I’m just now beginning to feel almost back to normal. Eeesh. Yes! The alarms need a much lower trigger point!

  70. Alex Stadtner says :

    Hello Michael,
    Thanks for writing. I’m glad our blog was able to make a difference in your life. Please stay in touch by receiving our quarterly e-newsletter or checking out our healthy building science blog page. Both are usually filled with useful tips to keep your buildings in safe and healthy operating condition.

  71. michael tostevin says :

    I had just purchased what I thought was a co detector, but because it plugged directly into a mains socket, and all my sockets are at floor level I was not content so I googled your page ,it confirmed my doubts, I returned to the shop and was able to convince them. ,with the help of your article ,that they were wrong and I have now purchased the correct alarm that has batteries and is fixed 15 cm below the ceiling , my family and I thank you for your excellent article, Michael , I live in Spain.

  72. Alex Stadtner says :


    If you’re really smelling combustion byproducts [released from gas-burning appliances (e.g., furnace, water heater, boiler, stove, oven)], then you do have a problem. If you have combustion appliances under your roof you should have a CO detecter. These are inexpensive and they save lives.

    I don’t know where you live, but if you’re in the US and your home is less than 2 years old and you’re inhaling combustion gases – I imagine your builder would still be on the hook to remedy the situation.

    A good “home performance contractor” or industrial hygienist would be able to test your home and determine if it’s indeed combustion byproducts. Do not ignore this suspicion. Get a CO detector and have a 3rd party check it out. CO is just one ingredient in a cocktail of emissions that spew from fuel-burning. If there is a faulty duct/flu or negative pressure situation that is resulting in backdrafting, you should proceed with caution and get it fixed ASAP.

    Best of luck,

  73. Maria Falla says :

    Hi, I smell what I read that must be a combustion of byproducts in my house, specially when I’m waking up. From what I read here, it’s not carbon monoxide, but is it still dangerous? My house is 2 years old…
    thanks for your help!

  74. Alex Stadtner says :

    Your standard practice sounds pretty good. Not idling in the garage and leaving the door open to allow for ventilation are both good practices. I doubt there is any significant risk of CO poisoning in this case, but you could always buy a CO alarm as a low-cost additional control measure.

  75. Garry Nonog says :

    I prefer parking my car in the garage with the front of the car facing out, basically backing the car into the garage. I normally turn the ignition off as soon as I’m parked and ted to keep the garage door open for a minute or two. On the other hand, I make sure to drive out of the garage as soon as I turned the ignition on. I try to keep the garage door open for a minute or two when parking or driving out. Is there any significant danger of CO in this case? I’d appreciate your input. Thank you.

  76. Alex Stadtner says :

    Yup. Hope this Carbon Monoxide Fact Sheet wasn’t too dull, but it certainly does address some of the more common mythes associated with CO. Hopefully your head doesn’t hurt too much and you’re not afraid to come back and visit the Healthy Building Science blog!
    Stay safe,

  77. For a moment there it felt like I was back in school, haha. Very informative article.

  78. Alex Stadtner says :

    Hi Susie,

    Good question about CO detectors. I’m afraid we don’t have any specific recommendations, and I don’t know which meters detect at the lowest levels, but I did find some ratings on Consumer Reports. They tested many models and rated them on a scale of 0-100, with 100 being absolutely perfect. Of course, none are perfect!

    Below are a few of the Consumer Reports ratings for Carbon Monoxide Alarms:
    “Recommended Models” = First Alert CO615 (87 pts), First Alert SCO501CN (90 pts)

    I was surprised that the nest Protect: Smoke + Carbon Monoxide only got 55 points.

    Another high-scoring model was the First Alert OneLink CO511B (89 pts).

    Best of luck!

  79. Sue says :

    Any recommendations on detectors that are reliable at detecting low levels of carbon monoxide?

  80. Alex Stadtner says :

    Hello Greg,
    There are good respirators with various types of absorptive materials and filtration media to address fine particulates and many VOCs, but I do not believe that you can effectively “filter out” Carbon Monoxide. It sounds as though the place really needs more ventilation. Perhaps it’s worth talking to your local OSHA compliance folks… They could certainly take measurements and offer advise on best practices.
    Good luck!

  81. greg says :

    hi i work in a warhouse that builds lawnmowers, and ive been trying to find a good face mask that would protect against carbon manoxide, welding gases, powder coating paint and god knows what else from the lazer machine. during the summer its not so bad in there besides the heat but in the winter time they close every door in the warehouse and i try to open it but the people in charge lock them closed witch im pretty sure is ilegal and a fire hazard. but they run like 8 to 10 lawnmowers and 3 forklifts at a time throughout a 12 hour work day every five weekdays. i wanted to know if there was a mask that could protect agaisnt these hazards effectivly. im not worried about how comfortable but i dont want to quit my job or call ocea and get fired so i want to know about masks

  82. Alex Stadtner says :

    We will respond to specific questions on the blog, or you can always call or email the office.

  83. Sanjuana Goude says :

    I’d like to find out more? I’d like to find out some additional information.

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