Can ventilation reduce radon? HRVs, ERVs, fans and open windows compared

Outdoor air has much less radon than indoor air. EPA reports the average outdoor level is about 0.4 pCi/L, compared with about 1.3 pCi/L indoors. So it seems logical that bringing in more outside air would lower radon. It can, but how much, for how long, and at what cost depends on the method. This guide explains what EPA says about ventilation options and when they make sense.

Two ways to lower radon

Radon reduction methods fall into two groups:

1. Preventing radon from entering, mainly through soil suction (sub-slab, drain tile, sump, block-wall, and submembrane suction). These reverse the pressure difference that draws soil gas in. EPA lists them at 50 to 99 percent reduction.
2. Reducing radon after it enters, through ventilation and dilution. These methods tend to be less effective and come with energy costs.

EPA's Consumer's Guide to Radon Reduction explains that systems with fans are more effective at reducing radon, and that most radon reduction systems cause some loss of heated or cooled air.

Heat recovery ventilators (HRVs)

EPA describes an HRV, also called an air-to-air heat exchanger, as a way to increase ventilation and help reduce radon. An HRV brings in outdoor air while using the heated or cooled air being exhausted to warm or cool the incoming air. That recovers much of the energy that would otherwise be lost.

EPA's assessment:

• HRV effectiveness is variable, and limited by the radon concentration and the amount of ventilation air available for dilution.
• HRVs are best applied in limited spaces, like basements.
• The HRV filter needs periodic cleaning and should be changed twice a year.

Energy recovery ventilators (ERVs) work similarly but also transfer moisture. They're often preferred in humid climates. The same limits apply: they dilute radon rather than stop it from entering.

Pressurization

EPA describes house or room pressurization, which uses a fan to blow air into the basement or living area from upstairs or outdoors, to create enough pressure at the lowest level to keep radon out. Its table lists basement pressurization at 50 to 99 percent, but notes it works best with a tight basement isolated from the outdoors and upper floors. Because it can bring in outdoor air with moisture and energy penalties, EPA suggests considering it only after more common techniques haven't reduced radon enough.

Natural ventilation: open windows and vents

Opening windows, doors, and vents brings in outdoor air and can lower radon quickly. EPA describes natural ventilation as giving variable and temporary reductions. Once windows close, levels climb back. It also means significant loss of heated or cooled air, and it's impractical in cold or hot weather. Natural ventilation can be a short-term measure while you arrange a permanent fix, but it isn't a solution.

Crawl space ventilation

For homes over crawl spaces, EPA says ventilating the crawl space, passively by opening or adding vents or actively with a fan, can lower indoor radon by reducing the home's suction on the soil and diluting radon beneath the home. EPA's table lists natural crawl space ventilation at 0 to 50 percent. In colder climates, pipes and appliances in the crawl space may need insulation. Submembrane suction is usually more effective. See radon in crawl space homes.

Exhaust fans can make radon worse

Not all ventilation helps. Exhaust-only fans, such as bathroom fans, kitchen range hoods, clothes dryers, and whole-house fans, push air out of the house. If there's no balanced supply of outdoor air, replacement air can be drawn in from the soil, increasing radon entry. Large range hoods in tight houses are a common example. Balanced ventilation like HRVs and ERVs, or dedicated makeup air, avoids this.

When ventilation makes sense

• Modest radon levels, just above the action level, in a basement or small area.
• Homes that need more fresh air anyway, such as very tight new homes.
• As a supplement to soil suction when suction alone doesn't get levels low enough.
• Temporarily, while waiting for a mitigator.

For most homes at or above 4 pCi/L, EPA's guide points to soil suction as the primary approach. EPA says some systems can reduce radon by up to 99 percent, and most homes can be fixed for about the same cost as other common home repairs.

Comparing the options at a glance

Method	EPA's typical reduction	Main trade-offs
Sub-slab or submembrane suction	50 to 99 percent	Small fan energy use, plus some loss of conditioned air
Basement pressurization	50 to 99 percent	Works best in tight, isolated basements. Moisture and energy penalties
Heat recovery ventilation	Variable	Limited by radon concentration and airflow. Best for small areas
Natural ventilation (windows)	Variable and temporary	Large heating and cooling losses, and not practical year-round
Crawl space natural ventilation	0 to 50 percent	Freeze protection needed in cold climates

Questions to ask before choosing ventilation

• What's my confirmed radon level, and how far above 4 pCi/L is it?
• Is soil suction feasible for my foundation? If so, why choose ventilation instead?
• How much outdoor air will the system bring in, and what will it cost to heat and cool?
• How will the system be balanced so it doesn't depressurize the house?
• Who will maintain filters and controls?

Test to confirm

Whatever method you use, test afterward. EPA advises a post-mitigation test within 30 days of installation, but no sooner than 24 hours after the system starts, and retesting at least every two years.

Key takeaways

• Soil suction stops radon from entering, while ventilation dilutes radon after it gets in.
• EPA lists soil suction methods at 50 to 99 percent reduction.
• HRVs and ERVs have limited, variable effect and work best in small areas.
• Open windows give only temporary relief, at a high energy cost.
• Exhaust-only fans can increase radon entry if makeup air isn't provided.