10 Key Terms To Know About Heat Pumps
Are you interested in a heat pump, but don’t know where to start? The first step is to make sure you understand the heat pump basics. This post explains 10 of the most common terms you should know before installing a heat pump.
Air source
Air source refers to how a heat pump transfers energy. Heat pump technology works by transferring energy between a nearby natural source and your home. Air source heat pumps use the outside air as their energy source. Air source heat pumps are the most common type of heat pump because of their ease of installation and affordability. Other natural sources of energy that a heat pump can use include water or ground.
Ducted and ductless/mini-splits
Air source heat pumps come in two broad categories: ducted and ductless. The type you can get depends on whether your home has ductwork. Homes that have ductwork typically have a furnace, can support a central air conditioner, and have grates or grills throughout the home to distribute conditioned air. Homes without ductwork are more likely to have boilers or electric resistance baseboards as the primary heating source and, without a ductless unit installed, typically use window units for cooling.
Most ducted heat pumps and central air conditioners work with the furnace’s air handler to distribute conditioned air through the ductwork. A good opportunity to upgrade to a ducted heat pump is when a central air conditioner needs to be replaced.
Ductless heat pumps are commonly called mini-splits and do not need ductwork to distribute conditioned air. Instead, ductless heat pumps directly condition the air of a room or area with an indoor head or cassette. Indoor heads are commonly mounted high on a wall.
You can read more about the differences between ducted and mini-split systems in our blog post here.
Secondary heat source
Most homes in Minnesota that have a heat pump need a secondary source of heating to maintain a comfortable temperature on colder days. This is because heat pumps’ capacity to supply heating gradually diminishes as the temperature drops. At a certain low temperature, a secondary heat source that is not dependent on outdoor air temperature may be necessary. This secondary heating system can be a furnace, boiler, or electric resistance.
Switchover temperature
The point at which your heating source switches from the heat pump to the secondary heating system is called the switchover temperature.
Capacity and cost are two important considerations when setting a switchover temperature. Capacity refers to the amount of heat a heat pump can move indoors as the outdoor air temperature decreases, while maintaining a comfortable indoor temperature. The capacity balance point is the temperature at which the heat pump can just meet the home’s heating needs. If the temperature continues to decrease from the capacity balance point, the heat pump will not be able to replenish the home’s heat at the rate required to keep a consistent, comfortable indoor temperature. An advanced, inverter-driven heat pump in a well-insulated and air-sealed home will have the lowest capacity balance point. Setting the switchover temperature to the capacity balance point minimizes how often the secondary heat source is used, which also reduces overall emissions.
Operating cost is the other main consideration. Depending on the prices of electricity and the secondary heating source fuel type (natural gas, propane, etc.), a switchover point can be estimated to keep overall energy bills as low as possible. This point is known as the economic balance point.
Homes that have propane as the secondary heating source will have roughly the same capacity balance point and economic balance point. In other words, the best way for these homes to save money is to run the heat pump as low as it can go.
Using historical prices as a guide, homes that have natural gas as the secondary heating source fuel type will likely have a higher economic balance point than capacity balance point. These homes will keep operational costs at their lowest with a more moderate switchover temperature. This can change, however, as gas prices fluctuate to higher-than-average values as was the case in the winter of 2021–2022.
Homes with electric resistance as the secondary fuel type do not have a switchover temperature. Instead, these homes can save money by installing an advanced heat pump that can provide heat to a very low temperature. This reserves expensive electric resistance heating for the coldest times of the year. Finding a heat pump cold-climate specifications is necessary in these cases capture savings.
A quality contractor will be able to discuss capacity and cost with you to determine a switchover you are comfortable with. You can read more about tips for choosing a heat pump contractor here and visit our Preferred Contractor Network list here.
Dual fuel
In a dual fuel setup (a dual fuel heat pump system), a heat pump (powered with electricity) covers all the cooling and part or most of the heating before switching to a fossil fuel secondary system.
Some electric utilities incentivize homeowners to set up a dual fuel heat pump system to reduce how much electricity a region needs during cold snaps. Electric utilities do this by offering dual fuel rates. In some cases, a dual fuel rate can halve the standard electric rate, making it much cheaper to operate a heat pump. Setting up a dual fuel rate typically requires an initial cost and may require a separate meter to be installed. Check with your electric utility to see whether they offer a dual fuel rate and what the initial setup involves. involves.
All-electric
In an all-electric heat pump setup (an all-electric heat pump system), a heat pump (powered with electricity) covers all the cooling and nearly all the heating. Supplemental electric resistance heating is turned on in very cold weather to help the heat pump maintain the thermostat setpoint.
Cold-climate
Cold-climate refers to a voluntary performance specification administered by Northeast Energy Efficiency Partnerships (NEEP) for air source heat pumps that can operate efficiently at low temperatures. Cold-climate heat pumps are often the highest performing units available and are the centerpiece of an all-electric system. NEEP maintains a searchable list to show if a particular heat pump unit has been submitted for and received a cold-climate specification. The list is best suited for advanced users. A simple way to use the list is to search a heat pump AHRI or model number; if the search returns a variety of heat pump configurations, the unit has cold-climate specification.
Home load
A home load is the amount of energy the home needs to maintain a comfortable thermostat setpoint. This energy is measured in British Thermal Units (Btus) per hour. Generally, larger homes and homes that are not well insulated and air sealed will lose energy to the outdoors more quickly, resulting in a larger home load. Contractors heavily weigh home loads when determining the size of the heat pump that is appropriate for your home. Home loads, however, are not fixed and can be reduced with energy efficiency upgrades. Read this blog post to learn more about how to measure your home’s efficiency.
Tons
Heat pump sizes are measured in US short tons, which signifies how much energy the unit can transfer in an hour. Each ton is 12,000 Btus. To put it in a streamlined example, a two-ton unit can move 24,000 Btus between your home and the outdoors each hour. Homeowners looking to use their heat pump for most of their heating should make this intention clear to contractors, as this will have implications for operational costs and the size of quoted units.
Inverter-driven
The most advanced heat pumps are inverter-driven, which means they can modulate their operation to best meet a home’s heating and cooling needs with less energy than a lower performing unit. For contrast, single-stage heat pumps can only turn fully on or fully off. Inverter-driven units, beyond being the most energy efficient, also run quieter, maintain steadier indoor temperatures, and dehumidify better in the summer.
