A study created by the Vent-Free Gas Products Alliance of the Gas Appliance Manufacturers Association (GAMA) and performed by Risk Sciences, LLC found that vent-free gas products do not generate enough humidity levels to foster mold growth. In the study, gas products were left on for twice as long as they were normally used according to a previous customer survey. After 100,000 stages and steps, it was shown that the relative humidity did not increase past 70% in 99% of cases. The study took into account factors like room volume, air exchange rate, temperature, initial relative humidity, and normal human activities.