Radon Removal Using Air to Air Heat Exchangers
Radon mitigation using air to air heat exchangers requires the building have low radon levels and a low natural ventilation rate. These restrictions mean air to air heat exchangers have limited use for radon mitigation.
They are typically only used in the following situations:
- A finished basement with the basement slab poured directly on clay or ledge
- A dirt floor basement
This technique involves installing an air to air heat exchanger, also known as a heat recovery ventilator (HRV). These devices function by bringing fresh air in from the outside and exchanging it with stale inside air. This is typically a box-shaped device with duct work leading to and from the outside along with duct work to and from the space being treated. As the air streams pass by each other the heat from the outgoing stale air is transferred to the incoming fresh air.
HOW AIR TO AIR HEAT EXCHANGERS REDUCE RADON LEVELS
When using an air to air heat exchanger for radon mitigation, the resulting radon air concentration depends on the following: initial radon concentration, natural air exchange rate and rated flow of the HRV unit. All of these factors determine whether to use an air to air heat exchanger as a radon mitigation technique.
Any space in a building exchanges air with the outside or adjacent building spaces. This occurs through doors, windows and smaller cracks and crevices. In general, the better insulated and sealed the basement or building space, the lower the exchange rate. A rock wall basement such as that found in an old farmhouse might have a natural exchange rate of 1 ACH (1 air change per hour). This means a volume of air equal to the total volume of the basement pass through the basement in one hour. A basement in a newly constructed home will have a much lower air exchange rate. In general, the lower the exchange rate, the easier it is to reduce the radon concentration by using a ventilation device. Through the use of an air to air heat exchanger, the natural air exchange rate can sometimes be doubled, tripled or even quadrupled and thereby cut the radon gas concentration in the air by 1/2, 2/3 or 3/4 respectively.
OTHER FACTS ABOUT AIR TO AIR HEAT EXCHANGERS?
An air to air heat exchanger increases fresh air entering the space. The heat exchange efficiency of these units is typically 70%. As a result of this less than perfect exchange, the fresh air provided by the HRV unit will be cooler than the air leaving the space. In addition, while the units do exchange heat, they do not exchange humidity. In Maine, sending humid air into the basement during the most humid days of the summer can result in condensation in the basement space and necessitate a dehumidifier.
Air to air heat exchangers are an option for radon mitigation in specific situations. Air & Water Quality has extensive experience in using this technique.