Radon Testing with ERV

That would also do it but in my case the unit was not balanced when installed and it was exhausting more air than was coming in resulting in a negative pressure and very high radon result. There should be a sticker on the unit indicating CFM in and CFM out signed by the technician who balanced it; I seldom see that sticker.

Those units (ERV/HRV) needs to be well maintained (most are not) or they will not perform as intended. A clogged air intake screen, filters, core, will result in poor performance and possibly elevated radon in the home.
Just before winter, I noticed a sharp rise in my radon gas detector (SafetySiren Series3) reading for my home and after further examination found the problem to be a defective servo motor. The servo motor purpose was to open the fresh air damper allowing fresh air to enter the home when the unit was on. This resulted in air being exhausted not being replaced, a negative pressure inside the home and elevated radon readings…

Question for those that turn off Energy Recovery Ventilation systems when performing radon test. Do you also close All Open crawlspace vents?

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No. That would create an abnormal situation. Marcel pointed out the big misunderstanding in this discussion, anything that lowers air pressure in the home will increase Radon readings. Consider the basics of stack effect and air movement through the home and you will see why this is true.

Why would closing the crawl space vents be abnormal? In many areas it is recommended to close them during the winter months.
Do think there would be no difference in the radon level if the crawl space vents were opened or closed?

Probably not true. If your venting the crawl space you would likely reduce the Radon levels in the conditioned space (where your testing). Same is true if you have a vapor barrier or not. A vapor barrier will reduce Radon levels in the floor above. Both items are valid mitigation techniques.

Yes, I understand that. So what happens when your Not venting the crawlspace?

My point is if the ERV is designed to run 24-7 then why would you turn it off?
If turned off to get different radon results, then it is turned back on while people are living in the home, doesn’t make sense to me.

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When testing for Radon it is the Protocol’s intent to test as close to normal conditions as possible. I don’t think we should should be trying to create the worst possible “Normal state” or condition the house “could be in” just to see if the house could have high levels during those Certain, theoretical conditions. Doing things such as “closing crawlspace vents because in some climates people close them during the winter” just to make sure you get the highest theoretical reading during your shorterm test is *not protocol. Remember exposure to radon is a long term effect.

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Where did anyone suggest doing that?

I believe you were the one that brought that up…

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You misunderstood me.

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Ok, My mistake then.