Heat Recovery Ventilation (HRV) vs Exhaust-Only Ventilation

What are some of the advantages of a balanced heat recovery ventilation strategy over an exhaust-only ventilation strategy?

Micky Dunegan, Zehnder Southwest Technical Sales Representative:   If you’re going to build a home with a tight building envelope with minimal infiltration and exfiltration, you need a ventilation strategy or the indoor air quality will suffer. When you are using exhaust-only ventilation (bath fans), you are unnecessarily exhausting heating or cooling and you don’t know where the make-up air is coming from.   The makeup air is often coming from pretty unattractive places: potentially under floors, between insulated walls, attics and other unattractive places to get outside air from.   Bath fans also tend to have higher wattage and energy consumption than continuous ventilation solutions.

How does an HRV contribute to the energy efficiency of a home?

Matt Groves, Zehnder Northwest Sales Engineer: If you don’t have an HRV, you would probably be using bath fans.  Bath fans take conditioned air inside the house and exhaust it out without recapturing any of the heat or the cool and then the make-up air enters the house at outdoor conditions through the cracks and openings in the house.  As a much better energy-efficient alternative, HRVs are constantly recapturing most of the energy of the conditioned air, either heat in the winter or cool in the summer and high-efficiency models are recapturing around 90% of this energy.  For example in the winter, if the outside temperature is about 30° F and your indoor temperature is about 70° F, the high-efficiency HRV will bring that fresh air in from the 30s and warm it up to within a couple of degrees of room temperature just by transferring that recaptured heat energy to the supply fresh air stream.

How does the HRV system help allergy sufferers?

Aubrey Gewehr, Zehnder Northeast Sales Engineer: The biggest way is that you’re controlling the air that you’re bringing in the house.   With a standard exhaust-only system, the air that makes up for the air that’s being exhausted gets pulled into the house through all the cracks in the building. Often cracks are full of dust, debris, and other unwanted contaminants. A Zehnder HRV controls the air that’s coming into the building. Then as that air gets brought into the building, it’s filtered before it goes to the heat exchanger. Our standard filter is about a MERV 7/8 grade filter which keeps most things out. Particularly for people who suffer from very bothersome allergy issues, we can upgrade that to a MERV 13 filter. The MERV 13 rated filter removes at least 90 percent of particles down to a third of a micron in size, which is extremely tiny. This level of filtration takes care of most of the pollen that would otherwise be drawn into your house.