Radon Mitigation using Air to Air Heat Exchangers

There are some situations which can be difficult (and very expensive) to mitigate. These include situations such as:

• A finished basement with the basement slab poured directly on clay or ledge.
• A dirt floor basement with extremely rocky or rubble-filled terrain.

In these situations and when the radon gas concentration is below 16 pCi/l, reducing the radon gas concentration by increasing the ventilation rate of the space can be considered.

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 and 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.

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 porous basement such as that found in an older un-renovated farmhouse might have an air exchange rate of 1 ACH (1 air change per hour). This means that the air in the basement completely turns over one time per hour. A tight space 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.

When using an air to air heat exchanger as a means to reduce the radon concentration, the resulting radon air concentration depends on the initial concentration, the natural air exchange rate and the flow rate of the HRV unit. All of these factors are considered when deciding whether to use an air to air heat exchanger to reduce the radon concentration in the space.

An air to air heat exchanger increases air freshness in the space. The heat exchange aspect of these units heat exchange within this unit is not perfect and the colder it is outside, the colder the fresh air released by the unit. In addition, while the units do exchange heat, they do not control 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 powerful dehumidifier.

Air to air heat exchangers (a.k.a. HRVs) are an option used to mitigate radon in certain situations. Air & Water Quality has extensive experience in using this technique.