Mitigating Radon

There are certain techniques that are used for almost every type of radon mitigation procedure. They include both passive and active radon systems: Sub slab depressurization, SSD with a crawl space, sealing openings, and air exchangers.

Sub slab depressurization (SSD)

Many homes have a “Sub slab depressurization” system, which uses a fan and PVC pipe to draw air from below the basement floor or slab on grade and then blow it above the roof, where it dissipates to outdoor air levels very quickly (0.4 pCi/L average). These are the most common systems and applicable to about 95% of the homes in our region

SSD with a crawl space

Does your home have exposed dirt in a crawl space? If so, the dirt will normally be encapsulated with a special plastic that is sealed to the perimeter walls. Next, a tee is placed in the pipe of the SSD system. The arm of the pipe will go into the crawl space and then through the plastic. The system draws air from under the sealed membrane and also removes most of the moisture coming from the soil. This is also a popular method for dehumidifying damp, musty crawl spaces and for mold mitigation.

Sealing openings

Sealing sump covers, holes and large cracks near the suction point is done as part of the mitigation process to prevent the loss of vacuum pressure near the vent pipe, which could prevent an effective extension of the vacuum the system creates under the slab.

Air exchangers

Some homes have unusual conditions under the floor or have large crawl spaces that are inaccessible or impossible to effectively encapsulate.In these cases an air-to-air heat exchanger (also known as a Heat Recovery Ventilator, or HRV) can be used to effectively reduce radon levels in structures that have radon levels less than 15 pCi/L. An HRV has two fans, one blowing air into the house and one blowing air out of the house. The fresh air coming into the house is tempered slightly so as not to cause a substantial energy penalty. The HRV reduces the radon through the process of dilution by exhausting the stale indoor air out, while bringing in fresh outdoor air that averages 0.4 pCi/L. HRV systems are more expensive than SSD systems, typically costing around $3,000.00.


There are certain requirements that must be followed for fan installation, as explained in the following points:

  • Radon vent fans are specialized devices, sealed units that will not leak or allow the radon flowing through them to escape.
  • Radon vent fans need to be fitted to account for the pressure difference and air-flow dynamics needed to reach radon reduction objectives. The type of fan is determined by the sub-slab conditions, the size of the slab and the extent of the radon problem.
  • For depressurization systems, vent fans cannot be installed in basements, or crawl spaces. National radon mitigation standards do not permit the fans to be located in the conditioned envelope of the house.
  • Radon fans are permitted in unfinished attics, garages (not below conditioned spaces) or on the outside of the building.

Finally, radon systems need to be screened at the exhaust discharge point (end of the vent stack) to prevent animals or large debris from going into the pipe and fan.

Only real radon fans should be used. In the U.S. there are 3 prominent radon fan manufacturers: Radon Away, Festa Radon Technologies, and FanTech. These fans are UV resistant, made of UL-listed durable plastic and have a watertight electrical terminal box. The radon fans we use have high efficiency EBM motorized impellers and thermal overload protection.

If you would like more information or assistance with installation of radon vents and fans please contact us for a free estimate.