This is Lesson 9 of our informal online course: Home Energy 101. All lessons by Philip Drader.
Fresh air is fantastic!
But there’s a little misconception that ‘A house needs to breathe” that I need to address before I talk about heat recovery ventilators. First let me state for the record, I’m a big fan of air tight homes. You’ll be more comfortable and save money while making your home more durable and quiet.
You need to breathe. Not your house.
I’ll say flat out that a house does not need to breathe. You need to breathe.
When your house “breathes,” it’s possibly pulling in contaminants. So after you’ve spent money conditioning your home’s air, it exhales warm moist air through the building envelope or into the attic space where that moisture can condense and cause problems like mold, mildew, and wood rot.
To say it in a different way, it’s impossible to make your home too air tight but it is possible to under-ventilate.
You want to control your home’s ventilation
We know uncontrolled ventilation isn’t good. Having air slip through cracks and seams in the building envelope when it’s coldest and windiest out is uncomfortable and expensive. So that’s why we air seal our homes by draft proofing.
What you want is controlled ventilation. When you control the ventilation, you get a consistent amount of fresh air, as you need it, whenever you run an exhaust fan or a heat recovery ventilator.
How to get fresh air into your air tight home
A significant amount of energy is used to condition the air we have in our homes. If you have a leakier home, you probably don’t need to run a fan to get more fresh air. But if live an air tight home or you’ve improved or are planning to improve the air-tightness of your home, you’ll want to know about heat recovery ventilators (HRV) and energy (or enthalpy) recovery ventilators (ERV).
Both are very similar in operation, with fresh air coming into the home through an insulated duct that passes through the heat exchanger core where it gets heated up by the outgoing stale air. After it is heated, the fresh air is ducted throughout the home. Stale air is pulled from the home and enters the other side of the core where its heat is given to the fresh air, before it is exhausted from the building via ductwork. It’s important to note that there isn’t any mixing of air. The air from one side cannot mix with the air on the other side.
There is a lot of variety on the market with varying efficiencies. Some HRVs are 60% efficient, while some models are well above 80%. Just be cautious when living in Waterloo Region with our cold winters. If you need a preheater, it is the wrong model for our climate.
You may hear the terms HRV or ERV thrown around and wonder at the difference. Wonder no more: an HRV exchanges heat between the air streams, while an ERV exchanges heat as well as moisture so your house won’t be as dry in the winter.
If you have an air tight home, I recommend that you get one or the other and learn how to use it properly.