The most important tools a home inspector has are their eyes, ears and nose.  Based on their knowledge of homes and their systems they use these to determine does something look right?  Does it sound right?  Does it smell right (or smell when it’s not supposed to)?

But often this isn’t enough and we need to turn to tools that can help us confirm what we see/hear/smell, or suspect but can’t quite determine using our own senses.

So today we will focus on two tools that can assist home inspectors in giving the home you own, or are considering buying a proper inspection – Combustible Gas Detectors and Carbon Monoxide (CO) Meters.

It should be noted that use of Combustible Gas Detectors or CO Meters is not a requirement for any home inspector.  But many, such as us here at Gumshoe Property Inspection LLC use them in a discretionary way as they allow for a more thorough, well informed inspection of the house.

Combustible Gas Detectors

Most people are familiar with the “rotten egg” smell of natural gas.  But did you know that natural gas on its own has no smell?  That’s right.  When natural gas first began seeing use in homes for heating and cooking, it was used in its natural state and had no smell.  

But in 1937 at the New London School in New London, Texas an undetected buildup of natural gas ignited and the resulting explosion killed almost 300 people, including many children.  Shortly after, the Texas Legislature mandated that an odorant be added to all natural gas used in the state and the rest of the U.S. and Canada soon followed.

Today the most common odorant used in natural gas is called Mercaptan.  It is harmless on it’s own, but it’s powerful smell is detectable by the human nose in even very small concentrations.

All flammable gasses will have what is called a Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).  For natural gas the LEL is 5%, which means that once the concentration reaches 5% of the volume of air available then a spark or sufficient heat source can ignite this mixture.  This is a very dangerous threshold indeed.

The UEL of natural gas is 15%.  Which means once we reach this level of concentration there will not be enough oxygen left for the gas to ignite or explode.  However this is still very dangerous since a person can be incapacitated by breathing an atmosphere that is too rich in natural gas which is also a life threatening condition.

In home inspections inspectors (including us) will use a combustible gas detector when inspecting gas powered appliances in the home such as water heaters, dryers, furnaces, and ovens/stovetops, or the gas meter.  Because if we do smell gas, we need an instrument like a combustible gas detector to understand what the concentration level, and therefore the danger level, is.

Further, if there is a leak that is causing a concentration level of 0.85% or lower you may not smell this with your nose, but a combustible gas detector can sniff this out easily.  

All that being said there isn’t any “acceptable” level of gas concentration whether you can smell it or not.  If it is detected the recommendation Is to always deal with it as soon as possible by calling a qualified plumber for appliance related problems or your local utility if the problem resides with the delivery source.

Carbon Monoxide (CO) Meters

Carbon Monoxide is an odorless, tasteless, invisible and highly toxic gas that is a byproduct of the incomplete combustion of carbon containing fuels like natural gas, gasoline or wood.  It is sometimes called the “silent killer”.

Deaths from carbon monoxide poisoning are on the rise.  The CDC reports that in 2022, 1244 people died from carbon monoxide poisoning – an 85% increase from 2012.

In a home, any appliance that uses natural gas such as water heaters, furnaces, gas fireplaces, stoves/ovens can be a source of carbon monoxide.

To give a good example – a gas water heater.  When a home inspector looks at the burner on a gas water heater we want to see a steady, blue color in the flame all around the burner.  This is an indication of efficient and more complete combustion.  Orange or yellow flames indicate incomplete combustion and the potential for more carbon monoxide concentration.  Remember earlier in the article when I wrote about inspectors using tools to confirm what we see or suspect?  This is one of those cases where an inspector will use their CO meter to measure the carbon monoxide levels around the water heater.

An inspector will also look at the vent for the water heater.  Even a well functioning water heater will produce some carbon monoxide from the burner.  But the vent system is what is used to safely direct these combustion gasses outside of the home.  But there can be issues that prevent this.  For example if the vent for the water heater is incorrectly sized it can create insufficient draft to draw the exhaust gasses up and out of the vent.  The gasses will then cool too quickly and fall back down the vent into the water heater space creating a dangerous condition.

So what are the symptoms of carbon monoxide exposure?  Well that depends on the concentration and duration of exposure.  Carbon monoxide is measured in parts per million (PPM).  Here is a list of symptoms you can experience based on concentration levels:

• 50 PPM – No symptoms for healthy adults
• 200 PPM – Slight headache, fatigue, dizziness and nausea after two to three hours
• 400 PPM – Frontal headaches within one to two hours.  Life threatening after three hours
• 800 PPM – Dizziness, nausea and convulsions within 45 minutes.  Unconsciousness within 2 hours.  Death within two to three hours
• 1,600 PPM – Headache, dizziness, and nausea within 20 minutes.  Death within one hour

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