Soil depressurization is by far the most economical and energy-efficient way to reduce and prevent high concentrations of indoor radon, but what do you do when soil depressurization is not achievable?
Scenarios include: inaccessible crawlspaces (2’ high or less that cannot be sealed and covered); extremely porous soils like karst or old mine tailing fields (which let air flow freely into the home sometimes by the hundreds of cfm); extremely abnormal radon levels (100s of pCi/L). Certain homes– “Houses from Heck” as we call them in the industry—just don’t respond to the traditional methods of soil remediation.
Sometimes the ‘solution to indoor air pollution is dilution’! Air-to-air exchangers, HRVs or ERVs depending on your climate, are typically hooked up to your HVAC system. Air exchangers take the “dirty” air from your home and send it outside, while simultaneously take fresh, clean outdoor air and bring it inside. These two air channels pass through the air exchanger thermal matrix (from now on I’ll call them HRVs, since that’s what we use in Colorado). The HRV (heat recovery ventilator) takes the thermal energy from the outgoing air and transfers it to the inbound air. So in winter conditions, 32-degree air can be warmed as much as thirty or forty degrees before it enters your home! These units typically only transfer thermal energy (sometimes moisture), but they’ll rarely transfer radon and other contaminants.
Properly-sized HRVs can prevent radon indoors by replacing all the air inside a home several times per day!! Outdoor radon concentrations average 0.3 pCi/L in most of the US, so your air exchanger can drastically reduce and prevent indoor radon with these systems running balanced. In extreme cases, you can damper the exhaust (“dirty”) air, which will positively pressurize your home. If you’ve read my other articles, you know that “your house sucks”. It sucks in air due to the stack effect and with that brings soil gasses like radon.
Now think of your house as a leaky balloon. Instead of sucking air in, with an imbalanced HRV you’re pushing air out through every crack and crevice. Ex. 200 cfm in, but 180 out, that’s 20 basketballs of air per minute (cfm) that have to find their way out of the thermal envelope of your home.
Conceptually, this is very simple but in practice you need to take into account many other variables so you don’t backdraft appliances or cause other nasty problems. It is always recommended you use a licensed radon professional and HVAC pro to perform set-up and installation of an HRV as a radon reduction measure.
For energy efficient HRVs, for radon reduction, see the Whole House Indoor Air Quality section of our website here. Modern HRVs like Fantech’s HERO Series filter out other air contaminants like mold, pet dander, outdoor allergens, and more!