Heat pumps are one of the essential technologies for a decarbonized life. They heat everything, from air to water to laundry, using electricity that can be cleanly powered by renewable energy. They are three to five times more efficient than natural gas, fuel oil or electric resistance systems. They also cool our homes and food (yes, a fridge is a one-way heat pump) which is increasingly important in a warming world.
Heat pumps are the heating and cooling system for our decarbonizing world. Their adoption is growing fast — last year heat pump sales surpassed gas furnaces, in the US, for the first time.
Source AHRI data and Electrify Now.
In Decarbonize Your Life, we’ll dive into all the ways that heat pumps can heat and cool, and in today’s post we’ll start with the biggest decarbonization move of all — using heat pumps to heat your home. Heating is the largest energy user in American homes, accounting for nearly half of all the energy used in our abodes.
Source: US Energy information Administration, 2015 Residential Energy Consumption Survey.
Nearly half (46%) of all US homes use fossil (aka natural) gas for heating, 5% use propane, and 4% use heating oil (source EIA). Of the 41% that use electricity for heating, only a quarter (13 million) use efficient heat pumps. The rest use inefficient electric resistance heating. That means only about 10% of homes nationally use heat pumps for heating (and this is similar worldwide). We need to grow that number dramatically in the coming years.
Source: US Energy information Administration, 2015 Residential Energy Consumption Survey.
Why Heat Pumps Are So Great
The International Energy Association puts it perfectly: “Heat pumps, powered by low-emissions electricity, are the central technology in the global transition to secure and sustainable heating.” Why? Their incredible efficiency can be combined with electricity that is 100% carbon free today (if you’ve got solar panels or participate in community solar or your utility’s renewable energy plan) or will be carbon free in the near future as renewable electricity quickly overtakes fossil fuels.
Beyond saving the planet, heat pumps provide a better heating experience, using a mellower and more constant type of heat than the on/off blast of a 3000-degree natural gas furnace. Heat pumps run constantly without temperature swings and filter and move more air throughout a house.
Finally, the technology is extremely advanced and cost competitive. Heat pumps have been around for many decades in the form of air conditioners and fridges, so the technology is mature. With new tax credits from the Inflation Reduction Act, heat pumps cost even less and families can get 30% off the cost of installation (more on tax credits and rebates from Rewiring America).
How Heat Pumps Work
Heat pumps move heat rather than create it. Think of them like a pump or sponge rather than an energy creator. We’re used to pumps moving water, but they can also move heat. A heat pump uses refrigerant to capture heat (even from cold air) and either pumps that heat into or out of your house. A fridge is a heat pump that works in one direction, pumping heat out of the fridge. Heat pumps for space conditioning do the same thing. In the summer they pump heat from your home to the outside, and in the winter, they reverse, pumping heat from outside into your home.
Types Of Home Heat Pumps
Heat pumps for home conditioning come in a couple flavors:
1) Whole house heat pumps pump heat into your entire home using ducts similar to a furnace or central AC system. For homes with existing ducts, this can be an easy change out of a fossil fuel burning furnace for a heat pump connected to the same duct system.
2) Ductless heat pumps, as their name implies, don’t use ducts to distribute heat, but rely on indoor units (aka “heads”) installed on the wall that link to an outdoor condenser.
We’ll discuss both in detail below.
Image courtesy of Electrify Now.
Whole House Heat Pumps
Ducted, whole house heat pumps can be divided one more time into two subtypes: constant speed and variable speed. Constant speed heat pumps (also called single or dual stage heat pumps) run at only one or two speeds. They are either on or off, full blast or nothing. They often have a lower upfront cost but a higher operational cost and usually require some type of backup (electric resistance or gas) heating system because they struggle to work efficiently below 20 or 30 degrees Fahrenheit. Constant speed heat pumps have a fan on the top of the outdoor unit and look like a classic boxed air conditioner.
Example of constant speed (two-stage) heat pump outdoor unit. Image courtesy of Goodman.
Variable speed heat pumps run at many different speeds, modulating up and down to maintain a certain temperature. They run much of the time, but at lower energy levels. Variable speed heat pumps can cost more upfront, but have lower operating costs because they are more efficient. Many of them also work in much colder temperatures. All cold climate heat pumps run at variable speeds (teaser alert: deep dive on cold climate heat pumps in an upcoming post). Variable speed heat pumps are also quieter because they run at slower speeds than the on/off blast of constant speed heat pumps. They have a more vertical looking outdoor unit than a constant speed heat pump, with a fan on the side rather than the top. Variable speed heat pumps can be used with both ductless and ducted heat pump systems.
Ductless system with variable speed heat pump. Image courtesy of Mitsubishi.
Ductless Heat Pumps
Ductless Heat Pumps (DHPs) provide heating and cooling by using an indoor device on a wall connected to an outdoor condenser (similar to typical AC). This means no air escapes through leaky ducts, so they offer the most efficient conditioning.
Ductless heat pumps are a no-brainer when you’re adding heating or cooling to a room without any ductwork. And DHPs also offer efficiency, economic and environmental advantages over a central ducted heating system. All DHPs use variable speed technology, meaning they tend to be more efficient than a whole house heat pump. A downside of ductless heat pumps is that when heating a whole house, you’ll need to install a “head” on the wall wherever you want heat or provide backup electric resistance heaters for rooms that don’t have a head. (We do a deeper dive on ductless heat pumps here).
Our Beloved Heat Pumps
Our house came with baseboard electric resistance heat in bedrooms and bathrooms in addition to the furnace. We decided to install two indoor heads in our then 1200-square-foot main home (in the open plan living room and master bedroom), and we use the backup electric resistance heat very occasionally in the other rooms. Combining heat pumps with rarely used, zonal electric resistance heat can be a strategy to reduce up front system costs. Our ductless heat pumps cost us phenomenally little to run and are a big reason our family’s energy bills are only one fifth the national average. We pay an estimated $250 a year (for 2,000 kWh of energy) to heat our home through the many rainy, chilly months of Portland winters.
Whether it’s ducted or ductless, in Oregon or Ohio, modern ranches or old craftsman duplexes, our family has used the mighty heat pump to stay warm, save money, and do our part to solve the climate crisis. So while heat pumps might not get as much love, they rank up there with solar panels and electric vehicles as crucial technologies that will decarbonize our lives without sacrificing modern comforts. Let’s get heat pumped up and put one of these amazing machines in every home ASAP.
This article is part of a series called Decarbonize Your Life. With modest steps and a middle-class income, our family has dramatically reduced emissions and is sequestering what remains through a small reforestation project. Our life is better for it. If we can do it, you can too.
Much of this content was pulled from the great experts we interviewed on webinars we host at Electrify Now. Check out our recorded webinars on cold climate heat pumps, ductless heat pumps and whole home heat pumps
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