Heat Recovery Ventilators (HRVs)
An HRV is simply a dual intake/exhaust fan that exchanges heat (energy) between the intake and exhaust. In other words, it allows you to exchange the air in a home without losing all of the heat (or air conditioned air) as you exhaust the old, stale air to the exterior of your home Here’s a brief description found in an owner’s manual of a unit we install quite often:
Why Install an HRV?
An HRV can be a very effective ‘tool’ in our arsenal against high radon readings. In certain homes, a standard Subslab Depressurization System just won’t work. Whether the aggregate below the slab is not porous enough, or the walls are old stone and emitting radon, the HRV can help.
In a recent home we visited in Kent OH, there were 2 factors at play which make an HRV the ‘best’ option. First, there was an exposed dirt crawlspace with literally hundreds of pounds of debris scattered around the 25×40 area. It would have taken several days to remove the debris from the 30″ high crawlspace which would have cost the homeowner a lot of money! Secondly, there were exposed granite foundation walls which also could be contributing to the high radon readings. The pre-mitigation tests showed concentration levels above 9.0 pCi/L, which is why the seller’s realtor asked us to provide a quote for mitigation.
The most cost-effective solution was to install a properly sized HRV in the basement which would exchange the air in the entire home at least once every 3 hours. We always oversize by a little bit, and chose a 200cfm unit for this 2000+ sf home.
What Needs to be Done?
In any HRV installation, two holes need to be cut into the home’s exterior walls. One intakes fresh air, and the other exhausts stale air. Next, a determination needs to be made as to where the stale air will be drawn from, and where the fresh air will be introduced back into the home. In the Kent OH example, we drew the stale exhaust air from the dirt crawlspace, and brought fresh air right into the main area of the basement.
The most important thing to remember when using an HRV for radon mitigation is to balance the system. This means that you must know how much air you’re bringing in, and taking out. If you take out more air than you bring in (due to restrictions from pipe size, bends in pipe/ducts, dampers etc), the basement will be under negative pressure. This means that the extra air being taken out needs to be replaced by something, and often that something is radon! So, an installer should balance the system in a way that pressurizes the basement – or, puts more air in than it takes out. This will effectively create an situation similar to a balloon, where the balloon itself is the basement walls/floor. The air inside the balloon/basement is trying to get out because there is an excess, which means no unwanted air can get in (eg the radon cannot seep into a basement under proper positive pressure). Balancing a system can be done using dampers or intentional restrictions of the ducting.
Putting it All Together
Using an HRV for radon mitigation is a very effective technique, especially in older homes. By exhausting stale radon-laden air and replacing it with fresh air, radon levels are reduced. By using the HRV to do so, only about 25% of the energy used to heat/cool the home is lost, as opposed to 100% without an HRV and simply introducing fresh air. If you would like more information on having an HRV installed in your home, give us a call at 330-267-9550!
Here’s a video walkthrough of the example we gave in Kent OH, where we successfully reduced radon concentrations from 9.0 pCi/L to .7 pCi/L: