Short-Term Real Estate Test: Closed-House Violation and Placement Bias
A measurement professional is hired for a pre-listing short-term test in a 1978 split-level home. A CRM is placed in the finished basement bedroom, 20 inches above the floor, not within 3 feet of an exterior wall, and the client signs closed-house instructions. The 48-hour test starts Monday at 4 p.m. Tuesday evening the homeowner opens the basement windows and sliding door for about five hours to clear paint fumes, then closes them. The CRM hourly readings across that period are 7.9, 8.4, 9.1, 0.6, 0.5, 0.7, 0.4, 8.8, 10.2, and 9.6 pCi/L; the 48-hour average computes to 6.9 pCi/L. The device sits 18 inches from a floor drain and a portable dehumidifier that cycles on and off. The client wants the report by Friday for a Friday closing.
1. Is this test valid under closed-house conditions? What does the CRM trace tell you?
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The test is not valid as conducted. Closed-house conditions require all windows and exterior doors to be closed for at least 12 hours before the test and throughout it, with normal HVAC operation and no exhaust fans running. The homeowner's five-hour window opening is a direct violation.
The CRM trace corroborates it: readings fall from 7.9-9.1 pCi/L to 0.4-0.7 pCi/L and then recover to 8.8-10.2 pCi/L. That pattern is consistent with dilution by outdoor air, not with a real change in soil-gas entry. Because the elevated portion of the test was not collected under closed-house conditions, the 6.9 pCi/L average cannot be reported as a valid result, even though it is above the action level. The dip also means the average understates the concentration that would exist under closed conditions.
Separately, the device was 18 inches from a floor drain, a known radon entry route, and within the cycling draft of a dehumidifier. Either could bias the readings and must be documented.
2. What options do you have, and what do you recommend given the Friday closing?
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Options: (1) invalidate and retest with a new 48-hour test; (2) extend the existing test to 96 hours or convert to a long-term test; (3) report the result with a caveat.
A caveat-only report is not acceptable for a real estate transaction because the result is not valid under the standard. Extending the same test does not cure it: the violation occurred during the measurement period, so the entire result is compromised. The defensible option is a new test.
To meet the Friday closing, start a new 48-hour test immediately, with closed-house conditions beginning at least 12 hours before deployment. If the device is deployed Tuesday night and the house stays closed, a valid 48-hour result can be retrieved Thursday and reported Friday. If the client cannot maintain closed-house conditions, a long-term test or a real estate-specific protocol with the buyer's agreement is the alternative. Document the invalidation, the reason, and the retest in writing, and do not simply recalculate the average.
3. What placement and interference issues should be documented, and how should they be corrected on the retest?
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Document the distance to the floor drain (18 inches) and whether the drain was trapped or open; the dehumidifier location, cycle, and whether its discharge air crossed the device; the device height and distance from exterior walls; HVAC supply and return proximity; and any other exhaust devices.
The floor drain is a potential entry point and the dehumidifier creates air movement, so placement should be corrected on the retest. Move the device at least 3 feet from the drain and outside the dehumidifier airstream, while keeping it in the breathing zone and away from exterior walls. Photograph the placement and note it in the report.
If the drain is open, recommend sealing it as a mitigation measure, but do not treat that recommendation as a substitute for a valid measurement. The professional's job is to produce a result that reflects closed-house conditions and a representative location, not to explain away an invalid one.