Photograph of a 120Vold carbon monoxide detector device Sources of Carbon Monoxide CO Gas in Buildings
Visual Inspection, Testing, Standards

  • CARBON MONOXIDE INSPECTION - CONTENTS: How to inspect buildings where carbon monoxide gas is suspected. List of building defects or conditions likely to create carbon monoxide hazards. List of building conditions likely to create combustion appliance backdrafting. Testing for Carbon Monoxide presence in buildings. Carbon monoxide hazards in buildings: a visual guide to inspecting for CO leak risks. Two quick combustion air requirement rules of thumb: Definitions of the "rule of 50" and the "rule of one inch per 1000 BTUs"
  • POST a QUESTION or READ FAQs about testing for dangerous levels of carbon monoxide (CO) gas in buildings including warnings about relying on test instruments
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How to perform a visual inspection to check for carbon monoxide hazards:

This article lists visible carbon monoxide gas hazards in buildings: things that you can see during a visual inspection that mean increased risk of carbon monoxide gas (CO) release and poisoning.

This text intends to assist readers in understanding these topics. However it should not be considered complete nor authoritative (no single article is satisfactory); we include additional advice and safety warnings about testing for dangerous carbon monoxide in buildings.

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Guide to Inspecting buildings for Visible Evidence of Conditions Likely to Produce Dangerous Carbon Monoxide Gas

Gas log fireplace (C) Daniel FriedmanIF YOU SUSPECT CARBON MONOXIDE POISONING GO INTO FRESH AIR IMMEDIATELY and get others out of the building, then call your fire department or emergency services for help. Links on this page also direct the reader to carbon dioxide gas information in a separate document.

Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases.

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Carbon monoxide poisoning can be fatal but exposure at lower limits can produce flu-like symptoms and headaches that are often mistaken for ordinary illness.

The fact that you cannot see nor smell dangerous carbon monoxide gas does not mean that there is nothing to look for when assessing the safety of heating equipment. Not only are there easily spotted installation errors (the first list below), there may be more subtle but easily visible errors if you know what to look for (the second list below).

Visible building conditions risking increased carbon monoxide hazards

This is by no means the complete list of errors that can cause dangerous carbon monoxide exposure in buildings, but here are some common foul ups outside of the workplace that can cause dangerous levels of indoor carbon monoxide:

Coal stove installed (C) Daniel Friedman

Barcelona Spain Gaudi chimneys (C) Daniel Friedman

Gas log fireplace (C) Daniel Friedman

Other clues which can suggest a risk of carbon monoxide hazards in buildings

Testing for Carbon Monoxide

In addition to the installation of CO monitoring alarms in buildings, a variety of electronic and gas sampling equipment is available to make spot checks for hazardous gases. We have and have used a variety of these devices under a wide range of conditions.

Watch out: While a "positive" indication of a gas such as carbon monoxide is an important indicator of a hazard, a "negative" or "not found" result is nothing to rely on.

The fact that dangerous levels of CO are not present in a building at a particular instant is absolutely no guarantee that dangerous levels of CO (for example) may not occur even moments later. For example, opening a window, turning on a fan or clothes dryer, closing a door, and similar innocent acts can significantly change air flow, combustion air, and other building conditions.

Therefore spot tests for dangerous gases should not be relied upon to guarantee building safety. This is why the list of visual inspection items and proper heating equipment maintenance are so important.

Suggestions and content additions are invited. CONTACT US with items to add to these lists.


CHIMNEY INSPECTION GUIDE contains detailed suggestions for inspecting building chimneys including the detection of blocked chimney flues or indications that a chimney may be blocked.

Effects of Carbon Monoxide Gases CO that may be mixed with Warm Flue Gases

Similarly, although a gas may be rated as "heavier than air", an inexpert building inspector or hygienist who tests for such gases only "low" in the building could be making a dangerous mistake.

Carbon monoxide gas, when produced by a heating appliance, will typically be mixed in with other combustion products and will be released as part of warm or hot flue gases that should be venting up a chimney. Therefore testing even for a heavy gas, if it may be mixed with hot flue gases, needs to include testing high in indoor spaces, not just down by the floor.

For this reason, if you call a fire department or emergency worker to test a building for the presence of a dangerous gas such as flue gases, leaks in natural or LP or propane gas lines or equipment, or carbon monoxide levels, even if the worker detects no gas leak present at the time of the inspection that is not a guarantee that the building is safe.

What should you do about this gas test reliability problem? Where there are reasons to be concerned about unsafe gas levels in a building, a more thorough building investigation is in order. Such an investigation includes at least

Safety Warnings About Using a Gas Detection Device to Check for Carbon Monoxide in buildings

In general, we should never detect the presence of carbon monoxide or "CO" in buildings beyond a possible brief and insignificant "belch" of gases from the draft hood of some heating appliances during appliance start-up when chimneys and vents are cold. In other words there should never be a continuous release of flue gases nor a stream of even low levels of CO in a building.

Watch out: Testing for any gas in a building by relying solely on test instruments can be dangerously misleading.

False positive gas test results: The TIF8800 or other equipment that can detect CO can detect very low levels of flue gas or combustible gases or carbon monoxide. But instruments such as the TIF 8800 that are not specifically designed for CO will also respond to other substances that are miscible in air.

Dangerous gas detection instruments work best in the hands of a very experienced building investigator and instrument user.

False negative results: any gas detection instrument is vulnerable to variations in building conditions or in the operation of mechanical systems in the building that can temporarily hide the presence of a dangerous gas leak. For example, a leaky heat exchanger in a heating furnace may leak detectable gases into the warm air plenum only until the blower fan comes on. Changes in building pressures, open or shut windows or doors, fans on or off, and other such variables can completely change the detectable presence of a dangerous gas indoors.

See GAS DETECTOR WARNINGS for additional recommendations.

Safety Suggestions: Install Carbon Monoxide Detectors in addition to Smoke Detectors

Carbon monoxide detectors are inexpensive and readily available, both as a battery-operated unit and as a unit that plugs into an electrical outlet in the home. No home should be without this safety protection, and homes with gas-fired equipment (natural gas or LP propane), space heaters, or other sources of risk should be extra cautious. Smoke detectors do not protect against carbon monoxide poisoning, and the opposite is also true. Carbon monoxide detectors do not warn of smoke or fire.

References & Research on Carbon Monoxide Testing at Heating Systems

Carbon Monoxide Gas Articles


Continue reading at CO ALARM CAUSES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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