In the middle of the 20th century, oil and gas furnaces replaced coal because they provided cleaner, more convenient home heating. Today, we’re in the middle of another home energy transition to more efficient heating and cooling. If your furnace burns oil or gas, or you rely on electric heaters, it’s time to learn about heat pumps, which provide significantly more efficient heating and cooling in many climates while reducing carbon emissions. Unlike furnaces, which are dedicated to heating alone, heat pumps operate year round, supplying both heating and cooling.
Air Source Heat Pumps
Heat pumps are not actually furnaces because they don’t burn fuel, but they’re the future of home heating and cooling in most areas of the country. According to the Natural Resources Defense Council, air source heat pumps are roughly 2 to 3 times more efficient than creating heat by burning fossil fuels like oil or natural gas. With broad adoption, the impact on climate change could be enormous.
An air source heat pump extracts heat from the air outdoors to heat your home in the winter, and reverses the process in the summer to cool your home. They’re more efficient because they move heat rather than burning fuel to release heat. Their efficiency translates into cost savings. The DOE finds that today’s heat pump can reduce your electricity use for heating by approximately 50% compared to electric resistance heating such as furnaces and baseboard heaters
Heat pumps have been a good choice in warmer climates for many years but weren’t efficient enough to work in cold climates. The technology has evolved, however, and air source heat pumps are effective in areas with freezing temperatures in winter. However, if temperatures in your area fall below 25 degrees F in the winter, you may need an auxiliary heating system.
Heat pumps have two parts: the air handler, which is inside, and the heat pump, which is installed outside. A refrigerant moves through tubing between the two units, absorbing and releasing heat. Warm air enters the home’s heating ducts in winter and cool air in summer.
Split-ductless systems have 1-4 indoor air handlers, also called mini-splits, that are installed high on a wall, eliminating the need for air ducts throughout the house. Because they eliminate the energy losses associated with ductwork, mini-splits can be 30 percent more efficient.
In the winter, very cold, low-pressure refrigerant absorbs heat from the outside air at the outdoor unit’s heat exchanger (1). The refrigerant then flows to the air-source heat pump’s compressor (2), which mechanically pressurizes the refrigerant, causing it to heat up. The reversing valve (3) directs the hot refrigerant to flow to an indoor heat-exchanger where the refrigerant transfers its heat to the indoor air (4). No longer hot, the refrigerant then passes through an expansion device (5), which makes it very cold. Because it is now colder than the outdoor temperature, the refrigerant can again absorb heat from the outdoor air to begin the cycle again (1). Source: goclean.masscec.com
Ground Source Heat Pumps
Ground source heat pumps work much like air source heat pumps but they extract heat from the ground and are one of the most efficient ways to heat your home. While air source heat pumps can reach 300% efficiencies (1 kilowatts of energy consumed produces 3 kW of thermal energy), ground source heat pumps can reach 600% efficiencies. As a result, they can reduce energy consumption by 25-50% compared to air source heat pumps. In fact, they can reduce utility bills by 70 percent over conventional systems, and they’re extremely reliable, with in-ground components that can last 50 years. However, installation costs are typically higher than either furnaces or air source heat pumps.
While the soil beneath your lawn warms and cools with the air temperature, if you dig four feet down, you’ll reach ground that maintains a temperature of 50 degrees year round. Geothermal systems take advantage of this temperature differential. Pipes are installed either horizontally in trenches or vertically in 300-foot holes drilled down into the earth. An average 2,000-square-foot home requires about 1,500 to 1,800 feet of pipe. Installation can be costly, which explains why many homeowners don’t take this route. But their high efficiency can translate into a remarkably quick payoff, within seven to eight years.
Geothermal heat pumps are expensive for a single home, but developers have started adding them to new developments, bringing green heating to many homes simultaneously. A Sense partner, EcoSmart, includes geothermal heat pumps in their new houses, delivering inexpensive, reliable heating and cooling.
Deciding on the heating system for your home
Each home is different, so do your research to decide which approach works best for you. Ask these questions to start the process:
1. How long will I live in the house? Calculate the payback period and ongoing costs so you know if the investment will pay off while you live in the house.
2. What’s best for my climate? Air source heat pumps are rated separately for warming and cooling operations. Choose models with the energy efficiency ratings that work best in your climate.
3. Is my home adequately insulated and sealed? By eliminating air leakage, you reduce heating and cooling loss so that whatever system you install can be smaller and less expensive.
4. Do I need to update my entire home or just a few rooms? Mini-split systems are a common choice for additions and they’re more energy-efficient than electric baseboard heating.
5. What’s the right size heating system for my home? Contractors use standard calculations to estimate the gas furnace your home needs. Similarly, heat pump systems are sized based on a combination of air volume, climate and how well insulated your home is.
6. How much space do I have outdoors? If you have enough space in your yard and plan to live in your home for many years, geothermal systems can be the most efficient choice.
The 20th century furnace was an innovation that kept homes warm for a century, but they burn fuels that add carbon dioxide to the atmosphere. Looking to the future, heat pumps offer a greener, more efficient technology that can lower your home’s carbon footprint and reduce climate change impacts while keeping your home comfortable year round.