Tuesday, November 3, 2009


We debated this question for months. Efficiency Vermont advised us to go with an ERV (energy recovery ventilator) but many homes in this region use an HRV (heat recovery ventilator). We did a lot of reading to make up our mind and spoke with a variety of folks including our electrician, Larry Wyckoff, who installed the system for us. Eventually we, in consultation with Larry, decided to go with an HRV.

What is an HRV? A heat recovery ventilator (or any sort of air exchanger) is critical for a house like ours that is super insulated. Because of the tightness of our walls, windows, and doors, our house will not "breathe" on its own. An HRV provides mechanical lungs for the house by constantly exchanging indoor air with air from outside. This helps maintain a high quality indoor air environment. A "heat" recovery ventilator also ensures that the fresh air coming in from outside is warmed up before entry. Here is a summary of how an HRV works from Popular Mechanics:

A heat-recovery ventilator (HRV) is similar to a balanced ventilation system, except it uses the heat in the outgoing stale air to warm up the fresh air. A typical unit features two fans-one to take out household air and the other to bring in fresh air. What makes an HRV unique is the heat-exchange core. The core transfers heat from the outgoing stream to the incoming stream in the same way that the radiator in your car transfers heat from the engine's coolant to the outside air. It's composed of a series of narrow alternating passages through which incoming and outgoing airstreams flow. As the streams move through, heat is transferred from the warm side of each passage to the cold, while the airstreams never mix.

What is the difference between an HRV and an ERV? According to the experts, HRVs make sense in climates that do more heating than cooling (e.g. northern Vermont). Again, Popular Mechanics:

Although an HRV can be effective in the summer months, when it will take heat from incoming fresh air and transfer it to stale air-conditioned exhaust air, it's most popular in colder climates during the winter. HRVs are ideal for tight, moisture-prone homes because they replace the humid air with dry, fresh air. In climates with excessive outdoor humidity, an energy-recovery ventilator is more suitable. This device is similar to an HRV, but dehumidifies the incoming fresh airstream.

You can read the article from Popular Mechanics here. Another good resource is this article from Eco Home Magazine.

For those of you building super-insulated homes, are you going with an ERV or HRV?