Very tight homes require some form of mechanical ventilation to maintain good indoor air quality. Heat recovery ventilators, HRVs, and energy recovery ventilators, ERVs, are balanced ventilation systems that bring in fresh air and exhaust stale air at an equal rate, neutralizing many of the negative effects from pressure imbalances created by other home ventilation strategies. When home improvements create the need for mechanical ventilation, consider an HRV or ERV system.

Both ERVs and HRVs provide steady, continuously balanced ventilation and recover approximately 60 to 70 percent of energy typically lost through one-sided, non-heat-recovery ventilation systems. Understanding the differences between the two options will help you choose the most effective mechanical ventilation strategy for a project.

While both units reclaim heat from the exhaust airstream, an ERV also absorbs moisture from the air. This makes ERVs the best choice for indoor moisture control. During heating season, ERVs can transfer moisture and heat from exhaust air into the dry outdoor winter air entering the home. Similarly, during summer months, ERVs can absorb moisture from warm incoming air and transfer it back outdoors, decreasing indoor humidity levels. In general, ERVs are more suitable for warmer climates.

HRVs take heat energy from warm outgoing air and transfer it to the colder air coming from outdoors, working in reverse during summer months. HRVs contain flat-plate heat exchangers. As heat travels through the core, it is transferred by conduction from the warmer to the cooler airstream.

Existing Homes details its mechanical ventilation specifications in section MV of the 2015 Specifications Manual. Please review that section to make sure your projects are compliant and have appropriate ventilation before you apply for an Energy Trust incentive.