The timing of the radon test depends on when closed-house conditions can be maintained. Throughout the 48-hour radon test (as well as 12 hours prior), all windows/exterior doors should remain closed, other than entry/exit. Ideally, there should be no contractors or work taking place in the home (like painting).
If you're testing your own home outside of a real estate transaction, the best time to test is when the house is "quiet." If you have young children, it may be best to conduct the test during weekdays when they're mostly at school and there's not a lot of entry/exit.
If you're planning a weekend trip or will be out of town for a few days, that might be the perfect testing period for closed-house conditions to be maintained without any inconvenience or restriction.
Home Buyers - New Construction
New construction is the best time to conduct a radon test - before anyone has lived in the home! If the results are elevated, the builder will generally pay to fix the home (have a radon mitigation system installed). With the builder's access to construction plans, it's the easiest time to install a radon mitigation system, and the home will be fixed forever.
The challenge with new construction is finding a good testing period when the house can be kept closed. Weekends are almost always the builder/project manager's preferred testing period, as contractors are less likely to be in the home on Saturdays and Sundays than they are during weekdays. Ask your project manager when the best testing period will be for your specific home.
For new construction homes, we typically conduct the test the last weekend before closing (or perhaps two weekends before closing if the house is complete in advance). We need the house to be as complete as possible, with the HVAC system operating normally, the weatherstripping installed on exterior doors, and (most importantly) free of contractors. We typically set up the radon test during the day on Friday and set it on a 12-hour delay to begin late Friday night/early Saturday morning. The test automatically shuts off after the 48-hour testing period, and we return Monday to pick up the equipment from the home. While we tape signs in English and Spanish on all exterior doors listing the requirements of the test, contractors tend to ignore the requirements and carry on with their work. For this reason, it's best to avoid all contractors and all work whenever possible.
**Before scheduling your new construction radon test, please check your builder's contract. If they give you the option to test after closing, that is always your best bet! Conducting the radon test after closing means you can ensure closed-house conditions are maintained and you can therefore trust the results.**
Home Buyers - Resale
If you're purchasing a home from a seller (not new construction), you have a lot more flexibility when it comes to scheduling the radon test. We can conduct the radon test during any 48-hour testing period where the house can be kept closed, other than minimal entry/exit. The test can be conducted before or after the home inspection, but ideally, not during the home inspection. The home inspector will be opening windows/doors, testing exhaust fans, opening the attic and crawlspace accesses, modifying the HVAC system, etc.
If you want to have the home inspection completed before conducting other inspections (like radon, pest, etc.), go ahead and schedule the radon test for a day or two after the home inspection is scheduled. That way, if you decide to hold off on the radon test as a result of the findings from the home inspection, you can cancel/postpone before the radon test has been set up in the home.