HRVs and ERVs have an obvious appeal: they give you a warm well ventilated home and stop you “emptying your wallet” into the atmosphere every time you open your windows. In winter, they can help save on your heating bills; in summer, they reduce the need for air conditioning. By keeping excess moisture out of your home, they’re better for your building, your furnishings, and your health (properly ventilated homes that are neither too hot nor too damp are less likely to harbor dust mites, a very common trigger of asthma.) and they help to keep the “climate” inside your home at a more constant level. Typically they retain about two thirds to three quarters of the heat that would normally be lost from your home through ventilation (some manufacturers claim 85–95 percent), so they really do save energy.
How much energy? According to British environmental auditor Nicola Terry’s calculations, HRV can safely cut the number of air changes per hour in a “leaky house” by about 50 percent, reducing the energy lost through ventilation by about 65 percent. A small amount of this energy is used to power the electric fans in the HRV system (typically about 50–100 watts, and as high as 300 watts in some cases), but there’s still a considerable energy saving.
On the downside, HRVs are expensive to install initially,and they’re not guaranteed to pay for themselves. On the other hand, money isn’t the only relevant measure; what price good indoor air quality? You’ll see most benefit from HRV in extreme climates: where the difference between the outdoor and indoor temperatures is greatest in summer, winter, or both. In milder climates, the benefits are much reduced and may, in some cases, be nonexistent.
Don’t forget that a typical HRV has a couple of small, electric fan blowers in it and costs money to run: you’ll only save money overall if you can recoup the installation costs and generate enough savings to cover the running costs as well. If you’re environmentally minded and money is less of an issue, saving more energy in heat recovery than you use in the system itself is obviously the thing you need to focus on. If you’re using HRV in particularly cold climates, you’ll need slightly more sophisticated equipment to stop the system from freezing up. HRVs also need regular maintenance, with filters that typically need cleaning or replacing every 6–12 months. Finally, if your home really struggles with damp (or you generate a lot of moisture in kitchens and bathrooms), you might need more than one HRV unit or a more sophisticated setup.