I’ve read in an Active Rain blog that radon tends to “build up” in a vacant house. I don’t know that to be true. There would be less plate out in a vacant house because of less air movement than in an occupied house and this would give higher working level readings. In a vacant house, windows most likely would be closed, fresh air intakes in the ACs would not be opened. … but this would be part of closed house conditions anyway. The blogger recommends airing out the house prior to beginning the closed house conditions. This is mostly information for real estate people. Is this airing out necessary for an accurate radon test? Does radon really “build up” in a vacant house? What do you think?
Why do we test for radon in a “closed house condition”?
We want to know the worst case scenario.
If they want to ventilate the house, why not just leave the windows open while you’re taking the test?
This is nothing but realtors trying to skew the results.
As far as EPA is concerned they would want closed house conditions to be the same as a vacant house for four days (the half-life of radon), however the national Association of realtors put pressure on the EPA because of time restraints and a real estate transaction. The EPA “settled” for a 48 hour period which in of itself is actually ludicrous as well!
No! You do not ventilate house.
Yes! An occupied house will have lower levels because of dilution from people coming and going and as you pointed out about air movement. Ludlow, Maine? Do you have forced air furnaces there? Or hydronic? I haven’t been to Ludlow for a while. I have a cousin in Lubec. 
Radon doesn’t build up above the point of saturation. Eventually radon will decay as fast as it enters the house. This is your working level.
Things always move from a higher energy to a lower energy. Radioactive material is obviously a higher energy. It will be replaced as it degrades when it reaches a point of saturation.
Thanks, David. What this guy was saying was air out the house, THEN do the closed house for 12, or maybe he even said 24 hours before the beginning of the test - all within the protocols. The airing out part seems unnecessary to me.
I do not do radon tests shorter than 4 days’ duration. I hope that the general public will begin to understand the advantages of the longer tests.
So you’ve heard of Ludlow, Maine!? Just this morning, I was trying to put information into a Facebook business account; they would not allow me to enter Ludlow as my town. I’m trying to convince Facebook that Ludlow exists. I don’t know the statistics, but I and most of the people I know heat with wood stoves. Many or most people in “town” (Houlton) use oil/hydronic, often supplemented with wood stoves.
As do I.
I must have brought it with me! 
I am 2nd Generation and all the clan that came off the farm in MA. moved to ME.
There are few left at this point.
Your at the end of I-95. That should account for something!
Again as for Radon testing, you should test (as you are) airing out is just nuts. You only open your windows for air conditioning in the summer (that day)!
This subject seems to have a trend these last few months.
More Realtor stuff…
Agreed. No one leaves there house open anymore. I imagine it would have been a lot less of a problem in the past. Open Crawlspaces, open doors, open windows.
I inform them that radon does not “build-up”, but my words typically fall on deaf ears. I tell my client that, regardless they will get a valid test. I let them ventilate the house. I tell them that we require closed conditions for a minimum of 12 hours, so who cares.
I start the test, close up the house, and add 24 hours to the test time. Test can run for up to 7 days, so irrational realtor fears and folk-lore have no net effect on my time or my service. My clients are happy, the realtor stops freaking, and I can sleep at night.
Airing out of a home for testing is a waste of time. Radon conditions and test results can fluctuate with exterior weather conditions and ground moisture saturation anyway. Close up the home, set your test, run it, pick it up, done.
Another myth perpetuated by the real estate community. Add this to statements about there not being any need to test in a new home, a home on a slab, etc.
Thank you everyone.
What missing here is the fact that when we test for radon, we are measuring radiation. Radiation from radon, like all other radiation decays at a specific rate. With radon, it’s half life is approximately 3.8 days. All radon that is captive in a structure will be cut in half in about 4 days. If radon numbers are high in a house, vacant or occupied, it is because the decaying radon is replaced with new radon at a rate greater than the decay.