Positive air pressurization as a radon mitigation approach

One of the most common aproaches to Radon mitigation is negative pressurization of the under-slab area created by installing a pipe and fan to suck air from beneath the slab.

Occasionally I run into homes which mesure high, but which have a crawlspace which would be a nightmare to try to mitigate… soil floor, stone rubble foundation and log floor framing with log braces down to the floor… forget the soil cloth… impossible to insulate the floor or install a membrane unless you use solid foam in which case forget future structural repairs.

I was wondering, If one could create positive air pressure in the crawl with a blower or fan, would it make much difference in radon levels?

What’s the proper term for the pressure of soil-source gas and what’s a typical pressure? Has positive air pressure been used for Radon mitigation?

Haven’t heard of + pressure for radon mitigation…yet. + pressure of the crawl space may introduce some radon, odour, moisture into the living space since the blown air will mix with crawl space air and be blown up through unsealed penetrations/cracks of the floor system. My approach would be to airseal the floor and crawl space perimeter well and put the whole space under a - pressure…no chance of anything getting up into house. With - pressure, have to be careful of flue gas spillage with naturally drafted combustion appliances though.

wouldn’t the introduction of blown air give a false reading

Yes, positive pressure is used in commercial applications. The HVAC equipment is there already and just needs to be adjusted.

Ask someone from OH. They often use a fresh air duct to the return side of the air handler. This will pressurize the house.

We use a similar system here in TN to control moisture in the crawl space.
A hepa filter is installed on the fresh air return (the incoming air is treated before it enters the house). The unit is balanced to the small positive pressure needed to push out the cs air. This will also work for Radon.

What reading are you referring to?
If it’s the Radon test results, it’s not false.


When you use the HVAC system to pressurize a dwelling, it must be set to run full time to maintain the + pressure at all times? What speed is it set at?
The fulltime running of an HVAC fan will add to the electrical bill!

Postive pressurization of buildings in cool/cold climates is frowned on (especially if a humidification system is active), since you will be driving moist air into the building envelope 24 hours/day and could cause hidden condensation.

I have heard of pressurizing exterior wall cavities with air to prevent exfiltration of warm, humidified interior air into wall cavities of a computer facility.

HVAC equipment with economizers are used. This is a controlled damper that brings in outdoor air. It is set to a minimum setting for the required fresh air requirements for the particular building use. An enthalpy controller will cool the building with up to 100% outdoor air if the “total heat” (wet and dry bulb) of the outdoor air is lower than the indoor air.

Yes, they do run almost 100% of the occupied time(often fan only), depending on weather conditions.

Remember, this is a commercial “public” building that is more concerned with air quality than just efficiency.

The unit does not have to run all the time to control the radon.
Pressurizing the building occurs from several units that do not run at the same time. This is often programed anyway to keep peek power usage down as commercial buildings are charged according to their peak load usage.

The required fresh air dilutes the radon.

Radon testing is an “Average” of the exposure over time. So yes, there will be up’s and down’s, but overall the concentration is pushed down below the required levels.

Only about 1.8 amps (residential).

If properly designed, humidity control is never a problem.

What are the designed running RH’s? and of course the climate?

Some of my first troubleshooting of pressure caused severe condensation from a humidified building was in the mid 1980’s. It was a new small hospital with a drive under canopy at the front door…in late December, it started “raining” under the canopy!!! Went to investigate in January (it was in another province) and found huge air leaks at the main wall/canopy intersection…"$hit" said the contractor, “don’t have to do good work here, it’ll all be covered in the end”. By the time it was done, it cost him about $9000-10,000 as they had us back to inspect the repairs.

You can pressurize with less air than trying to dilute the Radon.

1.8 amps is about 4 light bulbs. How much does lung cancer cost per year?

Any system must be correctly designed and installed. There are a lot of issues with using new technology with old standards (like what you posted).

You may want to look at

Consider looking at mitigation systems at

Doug Wall

That link is all about de-pressurizing, which is the most effective in residential.

But that was not the discussion.

mechanical ventilation is a positive pressurization system.
There have been thousands of positive pressure systems installed south of Orlando Florida.
sorry, I didn’t understand the discussion, I’m new to radon.
Doug Wall

Just keeping things on tract! :wink:

I live near Mineral, Virginia and have a radon system under the basement concrete. Here is my problem.

We had a large earthquake several years ago and after shocks in Virginia every sense and the radon levels get extremely high for weeks at a time after each shock. The radon system took care of the radon B 4 the earthquake and shocks.

I want to install a heat recovery system that will positive pressure the basement. Does anybody have any suggestions on the unit I need to install?