Carbon monoxide (CO) is a highly toxic, lighter than air gas which is most often found in an area surrounding a combustion source (e.g., a furnace, boiler or space heater) where there is insufficient oxygen to allow for complete combustion of fuel in use.

Deemed the “silent killer” because it is colorless, odorless, tasteless, and non-irritating, carbon monoxide is virtually impossible to detect without testing for its presence with the proper instrumentation in the hands of a professional. That’s why in this article we will focus on how to test for carbon monoxide in the home.

Preventing carbon monoxide poisoning

First and foremost, to prevent residential carbon monoxide poisoning, HVAC technicians must ensure that combustion equipment in the home functions properly. Additionally, combustion air openings (e.g., vents, flues, exhausts and ducts) should be kept open, clean and free of blockages such as dirt, dust, lint and trash.

It’s also important to never obstruct a draft hood, wind cap or exhaust vent on any combustion appliance. Nothing should be stored against or near the equipment that could restrict the air flow.

Sure, a roaring fireplace is always nice on a cold day in a private home or apartment; however, when combined with a marginal air flow to the furnace room, the fireplace might draw enough air to starve the furnace, producing a potentially hazardous backdraft of CO in the living areas.

Thus, the best way to prevent CO poisoning is to be constantly aware that CO is a deadly gas: testing is the only way to detect its presence.

The best way to test for carbon monoxide

Ambient CO test

There are two basic steps to an ambient CO check: 1) turn on the analyzer in fresh air and allow the 60 second CO-auto-zero-cycle to complete, and 2) with the probe disconnected, verify safe levels of ambient CO nearby the appliance and around the residence—as a courtesy to the homeowner.

While doing so, the maximum allowable ambient CO limits should be at top of mind:

Maximum Allowable Ambient CO Limits

CO Concentration

Effects of Exposure

9 ppm

The maximum allowable concentration for 24-hour exposure in any living / usable space (ASHRAE).

35 ppm

According to federal law in the United States, this is the maximum allowable CO concentration for exposure in any eight (8) hour period.

200 ppm

According to OSHA, this is the maximum allowable carbon monoxide concentration at any given time. Symptoms include headaches, fatigue and nausea after 2-3 hours.

600-800 ppm

In excess of all allowable limits. Symptoms include nausea and convulsion within 45 minutes and death after 2-3 hours.

3,200 ppm

In excess of all allowable limits. Symptoms include headaches and nausea within 5-10 minutes and death within 30 minutes.

CO air-free

It’s also important to note that the CO testing should be taken with an electronic analyzer that measures CO air-free. This calculated value determines the amount of CO that would be present in an oxygen free sample by compensating for the amount of excess air.

In other words, the CO air free measurement eliminates the excess air dilution caused by primary and secondary air. American National Standards Institute (ANSI Z21.1) specifies the use of PPM CO air free as a unit of measure when testing certain appliances.

How to get rid of dangerous co levels

If the level of CO is dangerous and exceeds acceptable levels, evacuate the area immediately and provide as much ventilation of fresh air as possible to the area where the CO is concentrated.

Appliance(s) should also immediately be turned off and repairs need to be made to such appliance(s) as soon as possible by technicians with the right instrumentation.

After determining, with right instrumentation, that the CO level has been reduced to a safe level, use your instrumentation to find the source of the CO and correct the conditions which caused the CO formation. (Note: Some local codes may require that you immediately shut down the equipment and notify the owner/operator.)

Ensure safe operating conditions

Ultimately, carbon monoxide is very dangerous gas that needs to be tested for by technicians equipped with the proper instrumentation.

While homeowners may feel protected from carbon monoxide by in-house detectors, such detectors only pick up levels that can be harmful, and they do not point to potential problems down the road.

Source: Bacharach, which offers a range of analyzers to test for the presence of carbon monoxide in the home, including the Monoxor Plus, the Intech, and the Insight Plus.