Buildings
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Before Choosing a Heating System… by Arnie Katz
Q: We're shopping for a new home, and one of our goals is to buy a house that is comfortable in the winter without costing a fortune. What really is the most efficient kind of heating system? A: The most important thing to understand is that any heating system can only be as efficient as the house it's in. The most "efficient" heat pump or furnace will not be able to keep you comfortable at a reasonable cost in a drafty house with a mediocre insulation job. It's like trying to fill up a swimming pool with cracks in the bottom. In that case, it doesn't matter how high the "SEER" (Seasonal Energy Efficiency Ratio) rating is on the pump. Unless you seal the cracks, you'll be pumping and pumping and pumping, trying to keep up with the leaks. The problem is how to know whether the house you want to buy is leaky or tight. Of course, no houses are advertised as "leaky" or "inefficient," yet I've been in many new homes that have serious insulation flaws and enough holes for air leakage that if you combined all the holes you would have a large enough hole for two cats to pass each other going in and out of the house. Two very large cats. Like tigers! The North Carolina Building Code includes insulation requirements. These levels do not guarantee a comfortable, economical house. They are simply the minimum standards allowed by law . While we often recommend higher levels than these minimum requirements, a bigger concern is not how much insulation is installed, but how well it is installed. A good insulation job requires meticulous attention to detail, not only by the insulation contractor but also by the frame carpenters. While many building inspectors do an excellent job, many others, unfortunately, have neither the time nor the training to do a serious insulation inspection. So let the buyer beware. You may want to ask the builder a few questions, such as:
How does the builder know the answers to these questions? Did he do his own inspection? Did he check with an infrared camera after the job was done, or do a visual inspection before the sheetrock went up? The next thing to ask about is how tight the house is. There are lots of ways to tighten a house — caulks, foams, gaskets, air barriers, and other methods can all be effective if properly used. Good, tight-fitting windows and doors with high-quality, long-lasting weather-stripping will help a lot. Some types of insulation, such as cellulose and sprayed-on rock wool, are effective at stopping air infiltration into the house. Ask your builder what he did to air-seal the house. Then ask if he had the house tested with a blower door, and what the test results were. The only way to know how tight your house is will be to test it . The fact that other houses built by this builder were tested and were tight tells you that he knows how to build a tight house, but it doesn't tell you about this particular house. In a recent survey by Advanced Energy of almost 100 new homes in North Carolina and South Carolina, we found that only one house met our "Exemplary Home" standard for air-tightness and less than a third were reasonably tight. On average, houses being built today are about twice as leaky as we recommend, with some nearly four times as leaky. And there was no correlation between how much a house costs and how tight it is. Some of the tightest houses I've tested have been those built by Habitat for Humanity in Durham and Orange Counties. Once you have a well-insulated house that is good and tight, then you can think about the heating and air-conditioning systems. What's the most efficient kind of system? The one that's sized and installed properly with a permanently sealed and tested duct system in a tight, well-insulated house. |
