Yes. Radon levels in a home, under typical operating conditions, will commonly reach a steady state with mild fluctuations about 12 hours after the house is closed up. Vacant houses will experience factors that may drive radon levels to lower or higher than normal averages, but the effect cannot be predicted. If the house is opened up for ventilation purposes prior to the test, it should then be closed up and a test started no sooner than 12 hours later. If short-term radon testing is being used, then the house has to be kept closed except for normal entry and exit, as if it were the winter heating season. It is recommended that the home’s heating and cooling system be operated normally for the season. If the average indoor level is 4 pCi/L, then it is expected that the radon level will be near to that average after 12 hours of a house being closed.