Jan 29, 2015

It’s one thing to seal a house up tight to save heat loss and reduce your heating bill. It’s another thing entirely to do balance than with maintaining good indoor air quality. One of the biggest issues with efficient houses is actually not the energy consumption, but maintaining a healthy indoor environment. Air has to be cycled, and that means making sacrifices when it comes to making your house “tight.” Granted, most homes aren’t tight enough and so have plenty of ventilation (and heat loss), but if you’re going to seal the house it’s good to keep in mind that, in the end, you still need air to move through. Assuming you don’t plan to leave windows and doors open year-round, or punch a hole in your wall, that means having a good ventilation system.

ASHRAE, which regulates this sort of thing, has all kinds of standards that engineers follow when building or renovating a home, but there’s plenty that homeowners can do on their own.

At the FLAT we are just starting to think about ventilation. An extreme winter last year showed us what can happen when air doesn’t move – humidity and smoke become difficult to remove, and one sick person suddenly poses a risk for everyone else sharing the same, semi-stagnant air. At the same time, however, we’re concerned about heat loss in the winter climate of western Montana.

One option is a heat recovery ventilator (HRV), increasingly common in more extreme climates and, as of 2014, required in certain state and national building codes. The HRV has two ducts – one to move air out of a building, and another to move ambient air in. Normally this would mean losing the heat of the outgoing air and replacing it with cold air. But the HRV’s ducts are passed through a heat exchanger that moves some of the heat of the outgoing air into the incoming air, thereby reducing the heat loss. In an ideal world, with 100% efficiency, this would mean that if you’re removing 80-degree air and replacing it with 40-degree air, you would end up with 60-degree air on both sides of the HRV. Obviously nothing is 100% efficient, so some more heat is still lost.

HRV (from: YellowBlue Designs)


As noted in the Energy projects link, however, it’s not as simple as poking a ventilator through the wall and plugging it in. There is asbestos in the FLAT’s walls, so any ventilation has to go through the ceiling, requiring extra ducts and duct insulation. The FLAT is currently considering whether this method is cost-effective.


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