Home Improvement Asked by Adam Hughes on March 30, 2021
Our basement has low-moderate radon levels, fluctuating typically between 1.5 – 4. We do have a subslab mitigation pipe, but it doesn’t work great. For other air quality reasons, we decided to install an ERV in our basement. After the ERV is installed, the HVAC guys will "balance" the pressure in our system, to ensure that the ERV is not putting an excessive pressure on the system.
For example, if the ERV put a negative pressure differential into our basement, this would cause the basement air to essentially "suck" in new air from under the house, effectively increasing radon level. Therefore, it’s standard to make sure the air pressure is balanced.
My question is – is it possible to actually do the opposite? Adjust the air pressure in my hvac system so that the basement floor is kept at a slight positive pressure? My logic here is that the positive pressure might act as a barrier to radon that otherwise would seep into the house through the basement subfloor and cracks and so forth. Is this possible/sensible, or do I just not understand what I’m talking about?
PS – I do understand there is mixed information about efficacy of ERV for radon mitigation.
Yes you can create a positive pressure and that may be a good thing as more of the air intakes will be on the upper floors. The difference between positive and negative is the amount of intake verses outlet vents. More vents pushing air than intake creates a positive pressure but you don’t want a large difference or the system will not heat well.
Correct answer by Ed Beal on March 30, 2021
Ventilation/ pressurization based solutions can be advised, and often are in commercial design. In residential a reduction of 50% average Radon readings is usually considered an upper limit with HRV/ERV mitigation. Modifications to the recommended HRV install with some exhaust drawn from near the basement or crawlspace floor can improve this. If you have measured your intake/exhaust volumes and adjusted for slightly more fresh air in , say 15%, than indoor air out (and you don't want to T into to your HRV pipes to modify) then you've done all you can with your HRV. Volume is not pressure. Measuring airflow alone gives you zero idea of across slab or exterior wall pressure differential. This is the force behind soil gas, Radon, entry. Maintaining a small level of vacuum, just a few Pascal usually, under the slab through your Radon pipe should not take more than the installation of a small quiet fan and should yield 75 - 95% Radon reduction.
Answered by RadonBC on March 30, 2021
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