Probabilistic assessment of the potential impacts of vent-free gas products on indoor relative humidity

A probabilistic analysis with the American Gas Association Research Division model and Crystal BallTM determined the contribution of vent-free gas appliances to total indoor relative humidity (RH). At least 20,000 simulations were conducted for each DOE Heating Region. Vent-free heating contributed to average indoor RH as little as 4% for DOE Region I, to up to 43% for Region V across all scenarios. The great majority of cases in all DOE regions were associated with RH levels from all indoor water vapor sources that were less than the 70% RH concern level for active mold and mildew growth.