Radon Testing with ERV

Good morning,

I am inspecting a new home with an Energy Recovery Ventilation system, the unit exchanges stale air from the home with fresh air from outside. Logically, I believe this must be switched off during the test as it introduces fresh air into the home and with would dilute the radon levels. Does anyone have any thoughts on this? I am compelled to test again with the system on just to see how effective it is at reducing radon, but that is more my curiosity than anything.

Thank you in advance for any thoughts or comments.

This is a system that is normally in an operational position at all times? Read through your training manual for radon.


The company that I sub out for my testing to turns them off. which is probably technically correct. However, the house should be at normal closed conditions. This would include the ERV running for a part of those 48 hours. I see it both ways.


I did before posting it clearly says turn off whole house fans for 12 hours before beginning the test.

You are a good guy but your name scares me.


That may be protocol but an ERV is meant to be ON.
I did a radon test in my home with the HRV ON and another test with the HRV OFF. And contrary to what some may think, the result was much higher with the HRV ON…
Some food for thoughts at: https://www.startribune.com/q-a-should-the-air-exchanger-be-on-or-off-during-a-radon-test/512773432/


The ERV should remain on and noted that it was running.


I agree, normal operating conditions.

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*Energy recovery or Heat Recovering ventilators: Normal operation of permanently installed ventilation systems that bring outdoor air into the home (also called air-to-air heat exchangers) is permitted to continue during closed-building conditions so long as the system is regularly maintained and continuously operational.”

Christopher made an excellent recommendation to mention the unit was operational during the test.

Maybe perform a test with the unit running and the unit not operational so that your client has more information.

That is my plan, I will follow protocol, my certification requires it. But I will test a second time if my initial test comes back with elevated levels, so my client has the whole picture. I appreciate the input and comments thank you.

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I was wondering about that also!!

There is another Robert Young that was very active in this forum, he and I are not connected. Seems like he used to tangle with folks in here quite a bit. Not really my style.

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One of the original members of “The WAFI List”!!

Please consider adding a Signature which helps us determine it is YOU posting and not the WAFI. Thx!!

Ya know, Marcel et al, I never did much radon testing, let alone with ERVs, so I was way off on my comment and will delete it. Sorry, for any confusion that I may have caused.

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Welcome to the forum, Robert.
A whole house fan is an entirely different thing than an ERV. They do 3-6 air changes an hour. That is a lot of air.

Pro-tip. You should also make sure bathroom ventilation fans are off and also range hood(s) are off.

I sometimes check on houses where i’m doing a radon test and find that someone has turned on a bathroom ventilation fan and/or range hood. That is sneakier (more sneaky, I don’t know the right word) than cracking windows, which can be seen from outside. Sellers cheat.


Good point Bert but that may also raise radon levels on the home as it causes a negative pressure and increase the stack affect. Home owner cheat may just bite them in the rear.

Best to be honest and let the test run in normal closed conditions.


Occasionally people try to skew the results by opening a second story window. Much to their surprise the numbers go up. More air flows through the basement cracks etc…


Get educated on the differences, then decide…


I don’t think that you were wrong with your comment, its just that I don’t agree with it. Around here, they unplug the unit while the test is on.

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No problem, Marcel. Radon is not my strong suit anyway. We don’t have much up here so I didn’t up-sell it…not my style anyway. :smile: