Thread: Radon Testing and ventilation

Did a radon test on a house for sale. The radon levels with a RadaLink monitor came back higher than 4.0 pCi/l. The sellers want to have another test done but want to open the windows and turn on fans to air out the house. They feel that since the house has not been lived in for 16 months, that airing out the house 12 hours before another test will lower the average radon level (test was done in an unfinished basement that the buyer wants to finish).

Is there any information out there that shows that airing out the house 12 hours before a test will or will not lower the average radon level (even a little bit) in a house during the test? I have read that opening and closing doors will not affect radon levels during a test and common sense tells me that airing out a house 12 hours before a test will not change the average radon levels during a test. That is why 12 hour wait time is needed.

There is another radon testing company that has informed the seller of this and if it is true, fine, I will learn something this weekend. But if it isn't true, I would like some written information I can refer back to.

Thanks ahead of time.

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Radon reaches equilibrium in 3.82 days.

The home being closed up for 12 months has little if any affect on the recorded reading.

House needs to be closed for 24 hours before test. So let them open it up as long as they want, as long as its closed for the previous 24 hrs. before test. And of course chargem.

"My house has sat vacant and closed up for (pick a time period). Won't the radon levels be higher than if it had been (a) lived in or (b) aired out before the radon test?"

I get this question a lot. I usually tell people, "No. It does not make that much of a difference." In fact, a short-term radon test is a measurement of the potential radon level in the house so why not measure its highest potential (per EPA protocols)?

I go on to explain that radon is radioactive and therefore does not build up over time. With water dripping into a bucket each additional drop of water adds to the amount of water in the bucket until it eventually fills the bucket and overflows it (ignoring evaporation). Radon is not like water dripping into a bucket; it does not continually add to the amount of radon in the house BECAUSE IT IS RADIOACTIVE. At some point - equilibrium - the new radon entering the house equals the radon that is lost to decay.

(There is also the natural fluctuations in radon levels from day to day, week to week, month to month and season to season. But that often only confuses people so I don't always mention that.)

Radon does not reach equilibrium in 3.82 days as stated above; it has a half-life of 3.82 days (meaning that after 3.82 days only half of the original radon will remain and after 7.64 days half of that half - or 25% of the original radon - will remain).

According to EPA protocols you can fully ventilate a house, close all outside doors (including the garage door) and windows for 12 hours and start your radon test. I guess EPA has determined that after 12 hours the radon level has reached equilibrium. (Not all the radon just entering the house is brand new. Some of it may have taken a longer path from its source to the house and decays before radon that took a quicker path from its source to the house.) Has anyone using a CRM verified that equilbrium is reached after 12 hours?

Actually, a house that has sat vacant may have a LOWER radon level than normal because it will not have any radon contribution from water (if the house is on well water or public water with high radon levels). Water must be used in the house for the radon to escape into the house FROM THE RADON IN WATER (e.g., hot showers, clothes washer, dishwasher, etc.).

Hi Kevin,

As Bruce stated that as long as you have 12 hours of closed building conditions prior and during the measurement you should have a valid test. (OF course other variables need to be correct to be valid i.e. wind etc).
The 12 hours prior to the beginning of a 48-hour test is to ensure dynamic equilibrium is reached.

"The United States Environmental Protection Agency (U.S. EPA) has designed a protocol establishing these standardized conditions, the so called “closed-house” conditions (EPA 1992, EPA 1993). When following closed-house
conditions, it is required that the house be closed 12 hours prior to the beginning of a 48-hour test to ensure dynamic equilibrium is achieved, that is, that the radon concentration in the house has come to a value reflective
of a steady-state condition where the radon coming into the home and the radon leaving the home are time independent."
Quote from Dr. J.F. Burkhart and R.E. Camley Physics Department University of Colorado-Colorado Springs 80918

Look to your training documentation for the definition of Dynamic Equilibruim and the 12 hours.


Two weeks ago I did a re-test not far from NW Indiana (In Illinois) where the original test was 6.2 pci/L and the retest came back as 1.9 pCI/L average. When I perform a retest in this situation I always do a duplicate test with
crm's (femto-tech). I make sure I security taped the windows in the basement and have the occupant sign a closed building conditions and non-interference agreement.
The two CRM's in this test came in at 1.8 and 1.9 (1.9 avg) with the temperature, humidity and Barametric Pressure showing no issues and the tamper tapes were not disturbed...
Using CRM's I usually come close to the original measurement...not in this case... I called the other testing firm and suggested they cross check their crm... It does happen but rarely in my experience.

What was the radon value in your test ????

Excellent comments so far. The information about decay rates was good. I tend to agree that testing in a previously vacant house should be lower, but I can't document that.

If radon testing results are very close to 4.0 pCi/L, it is important to remember that Radon levels DO vary naturally over time, and each testing method has normal levels of error. EPA recommends re-testing if the level is slightly over 4.0 to establish the true need before spending money on mitigation. Or, perform a long term test. Long term testing is not conducted in under 'Closed House' conditions, and is generally a more accurate measure since it allows for more natural living conditions; in my limited experience with long term tests, they have resulted in slightly lower levels than the standard 2-day short term test.

Location is critical!!! Placement near anything that affects air flow, laundry rooms (dryers), vents for gas water heaters & furnaces, etc can dramatically affect test results, even with testing units that are supposedly less responsive to affect by air drafts.

CAREFULLY review the documentation at Indoor Radon and Radon Decay Product Measurement Device Protocols | Publications | Radon | Indoor Air | Air | US EPA

Yes, test in the lowest level for worst case scenario. However, I prefer to test only in "Living Areas". The EPA does allow testing in unfinished basements, but I generally caution clients that testing in unfinished basements may not give the same result as testing after it was finished. So any radon test result in an unfinished basement that is very close the the 4.0 should be taken with a grain of salt. I have performed simultaneous testing at both basements and main floors of houses and consistently seen significant differences (between 2.0 and 8.0 pCi/L where the main level was less than 4.0).

Aside from the EPA protocals, to get a realistic conclusion of actual effects of Radon exposure, the home owner has to consider how that space is utilized because exposure levels depend on how much time people spend in those living areas.

Contrary to what the EPA says, I am not confident about the charcoal canisters (charcoal canisters are affected by air movement and cleaning chemicals). When I am told that a previous inspector got significantly higher readings than my testing, they were typically using the cheap charcoal canisters (or may not have placed them properly, or made sure the house was closed up).

Originally Posted by Terry Beck

Yes, test in the lowest level for worst case scenario. However, I prefer to test only in "Living Areas". The EPA does allow testing in unfinished basements, but I generally caution clients that testing in unfinished basements may not give the same result as testing after it was finished. So any radon test result in an unfinished basement that is very close the the 4.0 should be taken with a grain of salt.

Terry,

If you are doing a radon test for a real estate transation EPA says to perform the radon test in the lowest occupiable level of the home. Occupiable means an unfinished basement in your case. The current owners/occupants may not currently occupy the basement but the new or other future owners/occupants may finish the basement and have a bedroom, office, living room, play room, etc. in the basement where people could spend significant time.

If you are doing a radon test for a homeowner/occupant (not part of a real estate transaction) EPA says to perform the radon test in the lowest occupied level of the home. If the owner/occupant indicates that they plan to finish the basement or that they use the basement a significant amount of time then you would want to place your device in the unfinished basement.

Do you have any data to support your contention that finishing a basement may alter the radon levels in the basement? Unless great care was taken to "seal out" radon during a basement finish I don't see how simply finishing a basement would significantly affect the ability of radon to enter the basement. Admittedly, the use of the basement after being finished may have a noticeable impact on radon levels; a bathroom exhaust fan (creating a negative pressure in the space), an out of balance HVAC system (creating a positive or negative pressure in the space), etc. can affect the rate that radon is drawn into the basement.

I would like to see "before" and "after" radon test results for a few basements before and after being finished (normalized, of course, for seasonal fluctuations). Maybe I'll do my own study.

You may want to rethink the advice you are giving your clients. A radon test done before a basement finish would allow a homeowner to mitigate before the basement is finished (assuming the radon levels are high). The mitigator would be able to very easily caulk the slab/foundation joint, control joints, other joints, and slab cracks making the mitigation system more effective. The mitigator may also be able to more centrally locate his suction point (making the mitigation system more effective) and hide the piping behind drywall. If high radon levels are not discovered until after the basement is finished the opportunity to install a more effective, more aestetically pleasing and (possibly) cheaper mitigation system will have been lost.

Originally Posted by Terry Beck

I have performed simultaneous testing at both basements and main floors of houses and consistently seen significant differences (between 2.0 and 8.0 pCi/L where the main level was less than 4.0).

The general rule of thumb is that the radon level will decrease by about half when moving up one level. Of course, there are exceptions. (I am doing a radon test right now on a house where the tenant has measured radon levels about the same in the basement and on the main level (17 and 15 pCi/L respectively). He was using a 5-year-old plug-in radon monitor. I explained to him the lack of confidence I have in his device - especially the lack of yearly calibration. I am testing both levels with E-PERMs. It will be interesting to compare our results.)