Why You Should Be Scared
- Air conditioning costs U.S. homeowners more than $29 billion each year. Replacing a clogged filter can lower energy consumption by 5% to 15%.
- An estimated 98 million U.S. homes are under-insulated.
- Sealing air leaks and adding insulation can save up to 10% in heating bills.
- Uninsulated attics can increase energy bills by 67% versus a space that is fully insulated to local standards.
Step 1: Find the Air Leaks
Issue: Half the heat your house loses in the winter is through air leaks.
Solution: If a leak is big enough, you can find it by holding a stick of incense near doors, windows, and electrical outlets or switch plates. Whenever the smoke moves, you’ve found a leak. But the best option for finding leaks is a blower door—a fan mounted in a doorway that creates a pressure difference between indoors and out. (You can typically rent one for around $100 for four hours.) The door measures that pressure difference, along with the amount of air moving through the door. It has another effect, too: amplifying air leaks. If the outdoor air is 20 to 30 degrees cooler than the indoor air, you can feel the leaks with a wet hand. For a more accurate assessment, rent a fog machine from a party-supply store. (It should be around $30.) Set the blower door to blow air into the house, fill a room with fog, and then go outside and see where the fog is getting out.
Do I need an infrared camera? No, but they sure are fun. Along with helping you find air leaks and insulation gaps, infrared cameras are also useful for water-leak detection. Just look for irregularly shaped areas in the readout—they’re cooled by evaporating water. Above them you should find leaks.
Step 2: Seal the Air Leaks
Issue: You found a bunch of air leaks.
Solution: Most leaks can be fixed with a caulking gun and a can of spray foam. For wider gaps, use backer rod (soft, round foam strips that help the caulk bridge the gap). Caulk on the indoor side of a house lasts much longer than caulk on the outdoor side, because outdoor caulk is exposed to ultraviolet light from the sun, to rain, and to the stretching and shrinking of adjacent materials caused by changes in outdoor temperature. Leaks in a foundation can be closed most of the way with mortar if they are large enough, then closed up the rest of the way with caulk.
Air leaks around a window can be sealed with caulk if they are no larger than about 5/16 inch, or with foam and then caulk if they are larger. For electrical outlets, caulk around the box, or, even better, buy cover plates with gaskets. Air leaks around doors require weather-stripping products. Look for the ones that work by compressing a seal. Those that depend on one surface rubbing against the other will not last long. The most difficult part is the bottom of the door. Installing a saddle under the door gives weather stripping along the bottom of the door something to close against. Other products actually lower themselves down from the door when the door touches the frame and pushes a button.
Step 3: Cover Your Windows
Issue: Over the summer, the dominant source of heat gain in the house is sunlight into the windows.
Solution: If you’re buying new windows, buy something with a low-emissivity coating, which will help keep winter heat in and summer heat out. Otherwise, plant trees and install awnings or other types of sun shades. Or you can apply a thin film to the glass, such as . It blocks the infrared energy to keep the heat out.
Step 4: Get a Dehumidifier
Issue: As houses get more energy-efficient, air conditioners run for less time each day. Indoor humidity increases, making you feel hotter, and, in some cases, causing mold and mildew.
Solution: Most stand-alone dehumidifiers no longer rely on you to empty the collection bucket every time it’s full. Instead you run a hose directly to a nearby drain. You can also try a new built-in wall dehumidifier, such as the and the . Either one can be installed in the wall, connected to a drain and to electricity, set for the desired humidity percentage, and left alone.
How can I tell if it’s worth the money to add insulation in a particular area? If a wall or roof has no insulation, adding some makes a huge difference. If it has a little insulation, adding more is very helpful. If a wall or roof has a substantial amount of insulation, adding more does not make much difference.
Step 5: Insulate Your Water Heater
Issue: Exposed pipes mean lost heat.
Solution: If your water heater is electric, insulate its sides and top. Buy a roll of fiberglass insulation with a foil/paper backing, wrap it around the heater, and secure it in place with tape or wire. If the heater burns gas or oil, the top should not be insulated, as the insulation could block the air that needs to reach the flue. Any combustion-air opening near the bottom should also be left clear. Whenever possible, hot-water pipes should have at least one inch of insulation. Cold-water pipes should be insulated with ½-inch-thick insulation to prevent condensation.
Step 6: Seal the Furnace
Issue: The seams on most furnaces are not adequately sealed, allowing air to escape.
Solution: All joints should be covered with a layer of duct mastic, then a layer of fiberglass mesh, then another layer of duct mastic. All three can be applied at one time. There’s no need to wait for one layer to dry before putting on the next.
Step 7: Locate the Insulation Gaps
Issue: Incomplete insulation allows heat to be conducted and radiated through walls and roofs.
Solution: Look at snowmelt patterns, condensation patterns, or rain-drying patterns on the walls and roof. If one part dries more quickly than the rest, typically that’s a sign of missing insulation in that area. You can also buy a thermal camera from or . Both companies make attachments for smartphones that cost much less than a stand-alone camera, since they use your phone’s screen and memory. I find the black-and-white setting easier to understand than the color. On mine, the darker the image appears, the colder the surface. Hold it up to an area inside your house and the dark spots will reveal air leaks or missing insulation.
What’s the deal with all these energy-efficient light bulbs? A: Incandescent bulbs belong in antique stores. Fluorescent bulbs are almost as efficient as LEDs (and much less expensive), but they don’t last nearly as long. Most LED bulbs have such a long life that the fixture will probably need to be replaced before the bulb.
Step 8: Check the Attic
Issue: The upstairs is too hot in the summer.
Solution: Warmth is transferred through the attic to the living space mostly by radiant heat. Most houses already have insulation on the ceiling of the living space, but they can benefit greatly from adding a radiant barrier—a shiny, foil-faced sheet that can be stapled to the underside of the roof joists. Be sure to leave gaps around the edges of the radiant barrier to prevent condensation from forming on the underside of the roof. Or have a professional insulate the underside of the roof deck with spray foam.
Step 9: Test Your Heating/Cooling System
Issue: Many homes have systems that are too large for the space.
Solution: For less than $100 you can buy a data logger, a little device that you place next to your furnace to record the amount of time it spends running. Put another outside to measure the temperature, and you can tell if you have the right heating or cooling system for your space. If the system runs 50 percent of the hour on the coldest night (or warmest day, for an a/c compressor) for your climate, it’s twice as large as necessary and can be replaced by a much smaller model when replacement time comes. (If it is 15 percent oversized, leave well enough alone.) The same analysis can be done for a cooling system on a hot and sunny afternoon.
The Great Debate: Does turning the heat down at night save energy, or is the savings used when it has to run more in the morning?
Turning the heating temperature down at night and then back up in the morning saves a significant amount of energy, as does turning the air-conditioning temperature up when the home is unoccupied. Mathematically speaking, the amount of energy required to keep a house warm is equal to the difference between the indoor and outdoor temperatures multiplied by the time that this difference is maintained. Some thermostats, such as the , can be linked to your cellphone so that they know when you are getting close to home and can turn up the heat (or the a/c) before you get there.
Should I Insulate It?
- Exterior walls: Yes. The best time is when the siding is being replaced. Otherwise, you can insulate from the inside using blow-in cellulose or fiberglass material.
- Roofs: Yes. The best time is when the roof is being replaced. Spray-foam on the underside of the roof deck will also work.
- Basement walls: No. Insulating basement walls on the indoor side may cool the walls enough to condense water out of the air, causing mold. Follow local guidance.
Henry Gifford is a building scientist. He studies how buildings work and, just as important, why some don’t. He’s also the author of , the most useful home-energy explainer we’ve ever read, with nearly 600 photo-filled pages of information, infrared photography, diagrams, and insight.
This appears in the September 2018 issue.