Abstract: An energy recovery ventilator and method for monitoring and maintaining an environmental condition inside a structure such as a house, building, or dwelling is provided. The ventilator may include a housing having mating halves of a molded polymeric material, first and second chambers disposed within the housing to convey separate first and second streams of air, a heat exchanger configured to intersect the first and second chambers, a first fan to circulate the first air stream through the first chamber, a second fan to circulate the second air stream through the second chamber, and a fan motor driving the first and second fans. The ventilator may also be configured to prevent frost build-up in or on the energy ventilator, to provide efficient cooling, and maintain one or more desired environmental conditions.