As recently as two years ago, home energy retrofits might have been called esoteric territory best left to well-off eco-enthusiasts. But today, with increased attention and funding from the federal government and growing consumer interest, energy retrofits will soon become more common as people look to reduce energy bills and shrink their carbon footprints. The residential sector — through space heating, plug loads and more — accounts for about 21 percent of total energy use in the United States, according to the U.S. Department of Energy. But this drive to reduce energy consumption in homes in some cases has led to the marketing of “silver bullets” in the industry, from rooftop solar PV systems to tankless water heaters.
The truth is that no one solution is right for every house, under all circumstances. If someone tells you any differently, they’re selling you snake oil, says Matt Golden, president of Sustainable Spaces, a San Francisco-based home energy auditor and retrofitter. In the hope of dispelling some of these myths, below are our top five misconceptions about making your home more energy efficient:
Install solar PV as a first step: While a flashy solar system on your roof might get compliments from the neighbors, there are a raft of less sexy measures that give significantly more energy reduction per dollar invested. These are the classic energy-efficiency steps: insulating walls, floors and the attic; sealing ducts and air pockets; adding more efficient lightbulbs; and installing Energy Star appliances. Even investing in energy-saving mechanical systems like air conditioning, furnaces and water heaters should generally be done before — or at least at the same time — as adding solar PV (or solar thermal).
Consider this example from Sustainable Spaces: A 3.5-kilowatt solar PV system on a house that leads to about a 73 percent reduction in electricity use would cost around $28,000 (or about $15,000 with rebates and incentives), while a $10,800 energy-efficiency retrofit (or about $10,200 with rebates and incentives) would reduce electricity use by 25 percent and natural gas by 54 percent. The kicker: The PV system would yield an annual CO2 savings of 2.7 tons while the retrofit would remove about 3.6 tons, a 33 percent improvement with the latter. (The CO2 savings depend, of course, on the source of electricity, but the general trend would remain the same.)
All insulation is equal: Fiberglass batts are the most common type of insulation for homes, but their performance is highly dependent on the quality of installation. Gaps as small as a quarter of an inch between the batts and the wall framing are enough to cause dramatic reductions in their ability to insulate. Blown-in, or loose-fill, fiberglass or cellulose insulation is generally “far more effective” for retrofits than batts, according to Graham Irwin, a principal at Fairfax, Calif.-based Essential Habitat Consulting.
Double-paned windows are always beneficial: Not so much. There are potentially two major shortcomings. First, in the U.S., window manufacturers aren’t required to report testing data on air leakage, which could come, say, from a poorly insulated window frame or the lack of a tight fit between the frame and the glass, says Irwin. That means some double-paned brands (sliding windows are one glaring example) may actually leak a lot of air.
Irwin tells us if you’re replacing old, single-paned windows with even the leakier double-paned ones, odds are the new version is better. But to be certain, ask the manufacturer for leakage data. The second possible shortcoming: adding new windows with a reflective film, so-called low emissivity windows, which cut the solar heating in a house. While this might be good in the summer, in the winter you’ll want all the sun’s warmth you can get to keep heating bills down. The bottom line: You have to be smart about the windows you pick and where you place them.
You need a tankless water heater: The truth is that they don’t necessarily save energy. These systems, which provide hot water only as needed, have a much larger burner than conventional storage water tanks, which continuously, but more slowly, heat the water they contain. The rule of thumb, according to Irwin, is that if a household uses more than one-tank worth of hot water per day (about 50 gallons for a 2- to 3-bedroom house), then a conventional system is more energy efficient. That’s because the hot-water demand comes in discrete bursts, requiring in the case of the tankless system that large burner to turn on and off multiple times and undercut its potential energy savings.
Zeroing your electric bill means you’re using no (or little) energy: Generally speaking, homes rely on natural gas or petroleum for space and water heating. These can account for more than a third of a home’s total carbon footprint. A typical home furnace, for example, will burn about 100,000 BTUs per hour (or about 30 kilowatts). That’s equivalent to keeping 300 100-watt bulbs lit for an hour. Electricity, then, is only part of the battle toward achieving a net zero home, which produces as much energy as it consumes on an annual basis.
Images courtesy Wikimedia Commons and Kenmore (water heater).