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High levels of CO2 in soil can harm your health

Can carbon dioxide in the ground poison you? We ask an expert to find out.

Recently I received a call from a customer who claimed that every time it rained, the pilot light on his furnace went out, and he got so sick he was unable to leave the house. An HVAC specialist determined it was CO2 in the basement. Since I’d never heard of this, I asked Keith Volsted, President of VSI Environmental in Ingleside, Illinois for some fact on the subject.

Keith, is their carbon dioxide hidden in the ground around our homes?

CO2 in soil typically comes from natural decomposition. I have encountered several homes with elevated CO2, all built on farm land. Manure, fertilizers, nutrients are all added to the soil to enhance crop output. These products can combine and break down over time to create naturally occurring CO2 or soil gas which can be sucked or drawn into a home.

So is the CO2 being pushed into the basement?

Rarely will you find soil gas pushed into a home. Ground water tables rise very slowly, so they are unlikely to have a big impact except in rare cases. What does happen when it rains is soil capping, where the rain causes the soil to expand and tighten up not allowing soil gas to escape into the air around a home. At the same time, depending on the type of foundation the home may have, outside air that might penetrate dry soil below the foundation is cut off.

Surprisingly neither of these things alone causes the soil gas to enter the home. It is the home itself that is the driving force that literally sucks the soil gas from the ground.

So you’re saying CO2 isn’t being pushed in – it is being drawn in?

It is called the “Stack Effect” – warmer air rising, mechanical exhausts such as bath fans, clothes dryers, range hoods, furnaces and water heater exhaust all contribute to less air in the home than in the ground, it is this difference in pressure that draws the soil gasses into the home.

The simple solution is just to put a fan in a basement window, right?

Installing a window fan in a basement window that sucks basement air out only depressurizes the area more. Blowing fresh air into the basement would have a far greater impact on reducing soil gas entry; however this is not always practical year round. A far better approach is to address the problem at the source, the soil itself.

What do you mean?

The process is known as soil depressurization. It is a common approach to radon gas reduction, also a soil gas. By sealing sump pits, large cracks and openings in the foundation, and creating a negative pressure below the foundation just strong enough to overcome the normal air pressures in the home, soil gases of all kinds can be collected and safely discharged outside, creating a healthier home and in most cases a dryer basement.

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