A Fresh Look at Heating and Cooling the Home
Nothing gobbles up energy—and eats away at a homeowner’s budget—like heating and cooling the home’s interior. Considering the number of points in a traditionally-built home where air—along with the money you’ve spent to warm it up—leaks in and out, dad’s classic question of, “Are you trying to heat the outdoors?” comes to mind.
We’ll go into more detail about air sealing in another blog, but suffice it to say that this strategy has led to the need for innovative mechanical ventilation systems. In the past, mechanical ventilation wasn’t needed because homes were so leaky, but now that we’re building tighter structures, the building code requires it. In the last few homes we’ve built, we’ve chosen a heat recovery ventilation system (HRV). A HRV not only saves energy by reducing the amount of treated air that is wasted, it also improves indoor air quality.
The most important thing to understand about a heat recovery ventilation system is that it brings in fresh air and exhausts stale air, but it doesn’t let all of the heat in the outgoing air escape while it’s at it. A HRV, like the Zehnder Comfosystems unit that we’ve used in a number of homes, works like a radiator to pass most of the heat in the outgoing air to the incoming air rather than wasting the energy you’ve already used in heating it. This particular HRV unit is about 85 percent efficient. Simply put, that means that if the air going out of the house is 70 degrees and the air outside that’s coming in is 40 degrees, the HRV warms the air to about 65 degrees before it lets it into the house.
The incoming air passes through the HRV and goes on to a manifold. At the manifold, the air goes from a single big pipe to many smaller pipes, which in turn service all of the rooms that receive ventilated air. Usually this includes the main rooms like the living areas and bedrooms. Some rooms have return air vents. These are typically “wet” rooms like the bathrooms, laundry and kitchen from which stale, wet air is collected to be routed out of the house. The system also collects and exhausts excess moisture that might otherwise lead to mold and mildew.
This leads me to another benefit of an HRV—improved indoor air quality. By eliminating air leaks in the home and getting your fresh air from the ventilation system, you are ensuring that the indoor air you breathe is clean and healthy. As I said before, in an older house air is leaking in wherever it can find a way. A common scenario is that warm air, because it rises, will find a way to leak out up high, often through cracks between the wall and roof framing or through the cans around recessed lighting. The replacement air comes in from down low through leaks in the floor or bottom of the walls. This means that often the air you are breathing is coming from your crawlspace, most likely tainted with dust, mold spores, even the residue of pest sprays. By contrast, when you have a tightly sealed house and an HRV, the air you are breathing is coming from a known source and through a fine filter. You can choose filters based on your specific health needs and preferences.
A HRV ensures energy efficiency and a comfortable, healthy indoor environment in an air-tight home.
Check out the accompanying video on heat recovery ventilation for higher air quality.