Heat Pump Efficiency Guide
Especially popular in moderate climates, a heat pump is considered to be an energy-efficient alternative to a traditional heating and cooling system (i.e., a gas furnace with a central air conditioner). A heat pump gets its name because it “pumps” or transfers heat from one area to another instead of generating heat like forced-air furnaces or radiant heat boilers. For that same reason, heat pumps have shown the ability of operating at higher efficiencies than other heating systems.
To better understand the concept of heat pump efficiency, we’ll look at it from three angles:
- How is heat pump efficiency graded?
- What outside factors influence heat pump efficiency?
- How can the efficiency of heat pumps be increased?
How Heat Pump Efficiency is Graded
Heat pump systems act as both cooling and heating systems for your home. Because of this, heat pump efficiency ratings are published separately for heating and cooling functions. These efficiency ratings are calculated using different metrics.
Residential, air-source, heat pump efficiency ratings:
- SEER – Seasonal Energy Efficiency Rating is the most commonly used efficiency rating for both heat pumps in cooling mode and air conditioners.
- HSPF – Heating Seasonal Performance Ratio is used to measure a heat pump’s heating efficiency.
Keep in mind that the above ratings are used for typical split-system, residential, air-source, heat pump systems. You may also see EER (Energy Efficiency Ratio) cooling efficiency for ductless mini-splits and geothermal heat pump systems, and COP (Coefficient of Performance) for geothermal heat pump heating efficiency.
Heat Pump SEER Ratings
Because a heat pump system acts like a central air conditioner when it’s hot outside, heat pump SEER ratings are a measure of a system’s energy efficiency during cooling mode. It is a standard used to compare efficiencies of different heat pump units. It is the same standard used for residential, air-source, central air conditioner systems. And, like many other rating metrics, the higher the number, the more efficient the system.
SEER is calculated using the total amount of heat removed from the home during the cooling season, divided by the total number of hours the system operated during the same time frame. The calculation takes into account varying temperature conditions throughout the cooling season.
Minimum SEER efficiency: The Department of Energy has established 14 SEER as the minimum allowable cooling efficiency for residential, air-source, split-system heat pumps.
High cooling efficiency heat pumps: Generally speaking, models rated at 18 SEER and above should be considered highly efficient heat pumps. Some of the highest efficiency air-source heat pumps are rated at up to 20.5 SEER.
Heat Pump HSPF Ratings
When your heat pump is acting as your home’s heating system, efficiency ratings are published in terms of HSPF (Heating Seasonal Performance Factor). Much like miles-per-gallon for your car, a higher HSPF number equals a higher efficiency heat pump.
HSPF is calculated using the total amount of heat provided during the heating season compared to the amount of electricity used by the heat pump during the same time frame, taking varying outdoor temperature conditions into account.
Minimum HSPF efficiency: The Department of Energy has established 8.2 HSPF as the minimum efficiency for residential, air-source, split-system heat pumps.
High heating efficiency heat pumps: While some of the highest-performing air-source heat pumps are rated at 13 HSPF, anything about 10 HSPF should be considered to be a high-efficiency model.
Geothermal Heat Pump EER and COP
Geothermal heat pumps raise the efficiency stakes and can deliver much higher energy efficiencies than typical air-source models. Making an “apples to apples” comparison between geothermal and air-source systems is a little tricky because geothermal comfort systems use a slightly different method of measuring energy efficiency levels during heating and cooling modes.
Geothermal comfort system efficiency ratings:
- EER (Energy Efficiency Ratio): For cooling efficiency, geothermal systems use EER, which is similar to SEER, but measured at a specific temperature instead of varying temperatures throughout the cooling season.
- COP (Coefficient of Performance): For heating efficiency, geothermal systems use COP, which is similar to HSPF, but measured at a specific temperature instead of varying temperatures throughout the heating season.
EER and COP use a fixed temperature to calculate the rating – and because the heat source (ground or water) temperature doesn’t fluctuate as much as outdoor air temperatures, it’s a truer measure of the system’s actual capabilities.
Minimum efficiencies: The Department of Energy has established minimum efficiencies of 16.1 EER cooling and 3.1 COP heating for closed loop, water-to-water geothermal heat pumps.
High-efficiency geothermal systems: Geothermal systems come in a variety of options, but generally, high performing models can achieve energy efficiency ratings of 4.5 COP or higher heating and 30.0 EER or higher cooling efficiencies.
Outside Factors that Influence Heat Pump Efficiency
The decision to buy a heat pump, and decisions about which heat pump to purchase, will be influenced by a number of factors. While there is no “right” answer, there are plenty of options, and your individual priorities in each category will help you choose the system that is best for your family and your budget.
Preferred Energy Source
A heat pump is considered to be energy efficient because it heats and cools an area by moving heat rather than converting it from another fuel source. According to the Department of Energy, heat pumps can reduce electricity usage by 50% compared to electric resistance heating such as furnaces and baseboard heaters.*
Different types of heat pumps can draw heating energy from different sources. Each type has its own set of advantages, and all can be an effective solution, depending upon your needs, the design of the home, and your budget.
- Air-source: An air-source heat pump looks like a typical central air conditioning unit. It is powered by electricity and transfers heat energy from outdoor air to heat your home during the heating season. Split-system, air-source heat pumps include a unit inside the home and a unit outside the home. They generally cost less than geothermal systems, especially considering installation costs, but are typically not as energy efficient. Packaged air-source heat pumps are available as well with the entire system in one cabinet.
- Mini-split ductless: Mini-split ductless heat pumps are powered by electricity and also draw heat from outdoor air to heat your space. Mini-split systems are well-suited for providing heat in one space, because the indoor unit is designed to heat the area in which it is installed. However, there are systems that can accommodate multiple indoor units with one outdoor unit and can be used to provide comfort for a small home.
- Geothermal ground-source: These models pull heating energy from the ground to transfer heat into and out of your home. Geothermal, ground-source heat pumps can have higher efficiency ratings than air-source models, but can be more expensive due to installation costs for the required underground loop system.
- Geothermal water-source: These models pull heating energy from a water source such as a lake, pond, or underground aquifer. Geothermal, water-source heat pumps can be more energy efficient than air-source models, but more expensive to install. They also require an available water source near your home.
Ductwork in the Home
Most new homes in the U.S. are built to accommodate ducted, air-source heat pumps. If you are replacing an existing system, chances are you’ll probably want to stick with a similar type of ducted system. However, ductless, mini-split systems are another option when ductwork is either unavailable, in poor repair, or non-existent.
Ductless, air-source models are gaining popularity for heating or cooling room additions, older homes or spaces that don’t have existing ductwork, or rooms where the ducted system struggles to maintain comfort. Installation is fairly easy because no ductwork is required – the indoor and outdoor units are simply connected by a small-diameter copper refrigerant line and wiring for power to the indoor unit.
For year-round heating and cooling comfort, heat pumps work great in areas of the country with moderate temperatures. This is especially critical during the heating season. Once the outdoor temperature goes below 25⁰ - 30⁰ F, a heat pump can continue to provide heat. However, it will use more electricity to do so, which means higher utility bills. This is because there simply isn’t as much heating energy available as the outdoor temperature drops and the system will work longer to achieve the same indoor temperature. That’s why many air-source heat pump systems are installed with a supplemental heat source.
On the cooling side, the exterior temperature will affect heat pump efficiency and performance in the same way it would affect central air conditioning. Both systems are installed to provide adequate cooling capacity to your home at a specified outdoor temperature that makes sense in your area of the country (based on average high temperatures during the cooling season). And, both AC systems and heat pumps will work harder as temperatures rise outside.
Heat pumps can also be a good option for use in humid climates. Humidity inside your home can actually make you feel less comfortable, causing a natural response to turn down the temperature for additional cooling (and higher electric bills). High efficiency heat pumps generally dehumidify better than standard models because they are designed to run nearly continuously and at different cooling output levels (or different speeds). Because the cooling process helps remove humidity from indoor air, this means the higher efficiency heat pump spends more time dehumidifying indoor air (while consuming less energy).
Heat pump units are “sized” according to the heating and cooling needs of your home. While a larger home often requires a larger capacity heat pump, there are many factors involved, so sizing should be left to a qualified HVAC technician.
Sizing is an important factor that not only affects your comfort, but directly impacts the efficiency of the system as well. If a heat pump is undersized, it will likely be incapable of effectively heating or cooling a space. It may run virtually non-stop trying to meet the temperature you set on the thermostat. The result will be a higher electric bill and an uncomfortable home as well.
A unit that is oversized will sacrifice comfort and efficiency as well. An oversized unit may start running, heat or cool the home very quickly, then turn off until the home needs heating or cooling again. This constant on-and-off operation is hard on the system’s components, in addition to being very inefficient. A heat pump is most efficient when the temperature is maintained evenly, without the big ups and downs. So, having a unit that is oversized could result in inefficiencies and shorten the unit’s lifespan.
Taxes and Rebates
Higher efficiency heat pumps will cost more than mid- or standard-efficiency models. That is due in large part to the additional technology needed to increase efficiency. At the same time, this technology can also provide additional comfort benefits.
While it’s true that a higher efficiency heat pump can help to save money on your monthly heating and cooling bills, at times there may also be tax credits or local rebates available for some higher efficiency models. Some of the rebates come from local utilities for heat pump SEER and HSPF ratings, so check with the power company in your area see what’s available. For your convenience, follow the link to our HVAC Rebates page to see if there are rebates available in your area, and which models may qualify.
Ways to Increase a Heat Pump’s Efficiency
When you decide on an energy-efficient heat pump, you can sometimes boost your system’s overall efficiency by upgrading your indoor air handler to a top-of-the-line, communicating, variable-speed model. And by making your indoor unit a gas furnace, you can create a Hybrid HeatTM dual-fuel system that automatically chooses which fuel source – gas or electric – offers better energy efficiency for the conditions and temperatures outside.
There are a number of steps that you can take to complement your heat pump’s performance by making the home more efficient as well. You can seal in the savings by making the following improvements, especially if it’s an older home:
- Weather stripping doors
- Caulking windows
- Insulating and sealing ductwork
- Insulating walls in the home
- Insulating attic spaces