What You Must Know About Carbon Monoxide Detectors

Where home inspections are concerned, safety is the biggest value to look for…

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Carbon Monoxide (CO) is a tasteless, odorless gas. Detection in a home environment is nearly impossible by humans. The symptoms of CO poisoning are similar to the flue. Nausea, vomiting, confusion, sore muscles, headache, dizziness, light headedness, loss of balance, etc. Often, people who experience these symptoms simply go to bed thinking they are coming down with a cold. Some never wake up.

Red Blood Cells pick up CO more easily than Oxygen. If there is enough CO in your blood it can prevent the oxygen from getting into the body causing tissue damage or death.  You basically suffocate from lack of Oxygen.

During the heavy snow storms of 2013 on the east coast of the U.S. and Canada, a young boy died in their family car in the short time it took his father to dig the car out of the snow. Snow drifts blocked the exhaust pipe and CO entered the cabin of the vehicle. That’s how quickly CO can kill you.

The Limitations of Standard CO detectors

Standard CO detectors are not very sensitive by design. All readily available CO detectors must meet the requirements of Underwriters Laboratory Standard UL 2034. The problem is that the Standard requires CO detectors to only sound under the following exposure levels:

CO Concentration Parts Per Million (PPM) Response Time (when alarm must sound)

70 +/- 5 PPM

60 – 240 minutes

150 +/- 5 PPM

10 – 50 minutes

400 +/- 10 PPM

4 – 10 minutes


A UL 2034 listed CO detector is not allowed to sound for CO levels up to 64 PPM. The UL considers this a false alarm and a nuisance. The alarm will only sound for concentrations of 65 – 145 PPM after 1 – 4 hours. There is no protection against low-levels of CO.

The Danger of Long Term, Low-Level Exposure

All UL 2034 CO detectors state that they protect “Young Healthy Adults”. Young children, the elderly, those with blood or cardiovascular disease and fetus’ can be affected by long term exposure to low levels of Carbon Monoxide.

It is fairly common to have low levels of CO in a home. It may not exceed the PPM for a duration long enough to sound a standard alarm. This can result in daily exposure to CO which has been shown to cause Oxidative Stress in the group listed above. A study performed by UCLA finds that exposure to even tiny amounts of CO can lead to many disorders.[1]

To avoid Low-Level exposure you must purchase a high-end CO detector capable of detecting low levels of CO.

Installation Requirements in Existing Homes

Should CO detectors be on the ceiling? Can they be plugged in as many CO detectors are sold with a plug? Is CO lighter or heavier than air?

CO has nearly the same specific gravity as air. Air has a specific gravity of 1 and CO has a specific gravity of just over .965. So the CO detectors can be mounted just about anywhere with a few exceptions. They should not be mounted on the wall within 6 inches of the ceiling. This “pocket” is considered dead air that does not circulate or mix well with the rest of the air in the house.

CO detectors should be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms.

False Sense of Security

If you have young children, older parents, or someone with health issues living in your house, you should consider getting a “Low-Level” CO detector.


The best way to deal with Carbon Monoxide is to avoid it in the first place.

  • Never use a Propane or Kerosene heater inside
  • Never use a generator in the house or in a garage
  • Have your gas burning appliance checked annually
  • Check furnace and clothes dryer flue for signs of damage or obstruction. Birds and squirrels are known for building nests or hiding food in exhaust flues
  • Never run your car in the garage with the door closed – even for a few minutes
  • Replace your CO detector every 5-7 years

If you start feeling sick you should first move to fresh air and see if you feel better. Don’t just assume you are getting a cold or flu and go to bed. If you feel better outside, you may have been exposed to Carbon Monoxide in the home.

About the author: Philippe Heller is the president of The San Diego Real Estate Inspection Company. His multi-inspector firm performs thousands of inspections a year in San Diego.

To learn more, be sure to read the entire paper at www.sdinspections.com.


[1] UCLA Study Uncovers How Chronic Exposure to Tiny Levels of Carbon Monoxide Damages Hearing in Young Ears

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