A basement furnace can spread basement air through the whole house, and anything that exhausts air, like dryers, range hoods, and bath fans, can lower indoor pressure and pull in more soil gas. A good mitigation design accounts for both.
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Ohio's standards build HVAC into the job. The pre-install inspection notes systems that run continuously, and where natural-draft gas appliances share the basement, a backdraft test is required right after the fan is switched on, with any backdrafting corrected before the system goes into service. Test conditions account for HVAC as well: during a short-term test the furnace or air conditioner runs normally, but the air handler should not be set to run continuously unless it is labeled for radon control. Air conditioner condensate lines that drain beneath the slab need a trap, a reroute to a trapped floor drain, or a pump, so the fan does not pull air through them. After a furnace replacement or duct change, retest, because the pressure picture in the basement may have shifted.