The energy cost of exhaust-only or natural ventilation versus energy recovery ventilation can be easily demonstrated. Take a 2,500-square-foot house with indoor conditions of 70°F and 40% relative humidity, and outside air conditions of 30°F and 50% relative humidity. If we ventilate the house with 120 cubic feet per minute (prevailing wisdom of 0.35 air changes per hour) of outside air (as compared to no fresh air at all), here is how much the ventilation will cost us per month. This is due to the additional heating energy required because of the ventilation.
120 ft.3/min. × 60 min./hr. × (25.3 Btu/lb. – 9.06 Btu/lb.)* × 0.074 lbs./ft.3 × 1.25 efficiency × 24 hrs./day × 30 days/mo. × (1 × 105 therms/Btu) × $1.50/therm = $116/mo.
*Enthalpy of indoor vs. outdoor air (see psychrometric chart)