Installing an ERV or HRV – GreenBuildingAdvisor

Building Science

Achieve optimal indoor air quality through balanced ventilation

I installed my first balanced mechanical ventilation system, a ventilation strategy that supplies and exhausts equal volumes of air during operation, in 2004. It was a heat-recovery ventilator, or HRV. At the time, my understanding was that the equipment was used to control interior humidity in homes during the long northern Minnesota heating season. Today I have a much better understanding of how these systems work and why they are important. They provide a lot more than wintertime humidity control.

I did some training a few years ago that included a deep dive into balanced mechanical ventilation. We learned that when compared to other ventilation strategies (see “Three Ventilation Strategies”), balanced ventilation can prevent pressure imbalances in a home that cause problems with combustion appliances. Balanced ventilation can also reduce uncontrolled air leakage within structures by maintaining a neutral pressure balance inside the home, and it can reduce the related problems with moisture in the building assembly that result from a structure becoming pressurized or depressurized.

During that training, something the instructor said stuck with me. Though this type of ventilation has all these benefits for the home, heat-recovery ventilators and energy-recovery ventilators (ERVs) are installed more for the occupants than for the home itself. The instructor said we should be calling them “fresh air machines.”

Having the ability to control where the fresh air is coming from, and how much fresh air enters the house, is important. In the past, homes exchanged indoor air with outdoor air through building defects—unsealed gaps and cracks (and sometimes large holes) in the building enclosure.

How much air infiltrated and exfiltrated a home was based on wind and the stack effect, as well as combustion appliances, clothes dryers, and other exhaust fans. Air-sealing has reduced the natural air exchange of a home, but…