HSPF: Heat Pump Efficiency Explained

A heat pump’s HSPF rating is one aspect to consider when shopping for a new unit. Heat pumps are energy-efficient heating and cooling systems that transfer heat between buildings and outside sources. Different efficiency rating systems exist to measure the separate elements of heat pump performance.

Choosing an energy-efficient heat pump saves money on heating and cooling costs and reduces a home’s carbon emissions. Tax incentives and rebates provided in the 2023 Inflation Reduction Act for heat pumps help consumers installing new systems save additional money. Some consumers should focus on HSPF ratings, while others should concentrate on SEER or COP ratings.  

1. Determine the heat pump’s energy input over one heating season in watt-hours. Household electricity use is measured in kilowatt-hours (kWh) and must be converted to watt-hours.  

1 kWh = 1,000 Wh

20,000 kWh x 1,000 = 20,000,000 Wh

2. Insert the heat pump’s heating capacity and energy input over one heating season to the HSPF equation. The equation’s result is the heat pump’s HSPF rating.

160,000,000 BTUs / 20,000,000 Wh = 8 HSPF

Efficient heat pumps with higher HSPF ratings use less energy and have less environmental impact than units with lower HSPF ratings. HSPF ratings are essential to consumers wanting to reduce energy costs and decrease carbon emissions.

Highly efficient heat pumps save money on heating costs, but they are more expensive and aren’t recommended for everyone. People in cold climates benefit the most from efficient heating, while standard heat pumps are sufficient for consumers moving in the near future or living in warm climates.

High HSPF ratings are more significant in areas with cold, long winters where heating is heavily relied upon and less critical in moderate climates where heating is seldom used. Basic-efficiency heat pumps (8.8 HSPF) suffice for warm climates without extreme temperatures. People in moderate climates that want better energy efficiency might prefer moderate-efficiency heat pumps (8.8 to 9.5 HSPF). High-efficiency heat pumps (9.5 HSPF and higher) benefit homes in cold climates.

Low HSPF ratings don’t signify inefficiency, however. The Department of Energy has established efficiency standards for heat pumps and other appliances manufactured in the U.S..

According to the 2023 HVAC efficiency standards, the minimum HSPF rating for split-system heat pumps in all regions is 8.8., which correlates to 7.5 HSPF2, a new measure introduced in 2023. The minimum rating for package heat pump units is 8.0 HSPF or 6.7 HSPF2.

A split system heat pump includes indoor and outdoor heat pump units and an air handler or furnace. The indoor and outdoor components exchange heat between the indoor and outdoor air. The air handler or furnace houses the indoor unit and uses a blower to distribute the cooled and heated air through the home’s ductwork. Some air handlers also accommodate backup heating systems.

Standard heat pumps with backup heating systems are satisfactory for moderate climates, but heat pumps in cold climates require more than basic backup heating systems to maintain indoor temperatures. Dual fuel split systems and cold climate heat pumps are two alternatives.

• Standard split system: This heat pump system includes basic indoor and outdoor units and an air handler. The heat pump provides the home’s heating and cooling. Some systems also include electric heat strips in the air handler for auxiliary and EM heat. Like all electric resistance heaters, heat strips have high operational costs and are only intended for intermittent backup heating.
  
  

• Dual fuel split system: A dual fuel heat pump system includes standard indoor and outdoor heat pump units and a gas or oil furnace. The heat pump provides the home’s cooling and most of the heating. The furnace takes over heating when the outdoor temperatures drop, and the heat pump loses efficiency. A dual-fuel system doesn’t require a separate air handler; the furnace’s blower distributes the cooled and heated air.
  
  

• Cold climate heat pumps: A cold climate heat pump system includes indoor and outdoor units with high HSPF and COP ratings and an air handler. Cold climate heat pumps are more efficient than gas furnaces and rated to at least 10 HSPF and at least 1.75 COP at 5°F. Cold climate heat pumps can also be incorporated into dual fuel systems for regions with long, bitterly cold winters.

While air-source heat pumps use HSPF ratings to measure heating efficiency, geothermal heating and cooling systems use COP ratings. The COP (coefficient of performance) is a related measurement representing the average space heating rate at a specific temperature. The COP is the ratio of the heat the system transfers compared to the energy input. Therefore, a system with 2.34 COP moves 2.34 times as much energy as it consumes.

HSPF ratings can convert to COP ratings to compare different types of heat pumps by multiplying the HSPF rating by 0.293. For example, a heat pump with an 8.8 HSPF has a COP of 2.58 (8.8 x 0.293 = 2.5784) and moves 2.58 times as much energy as it consumes.

Heat pumps provide cooling and heating, a key advantage of heat pump systems over other HVAC systems. Separate rating systems measure heating and cooling efficiency. HSPF represents heating efficiency, and SEER (seasonal energy efficiency rating) measures cooling efficiency. Air conditioners, which operate like heat pumps in cooling mode, also use SEER ratings.

The SEER rating reflects the amount of heat removed from a home compared to the energy input over one cooling season with temperatures ranging from 65 to 104°F. As with other ratings, higher SEER numbers indicate more significant efficiency.

Heat pump SEER ratings are more important than HSPF ratings in warm climates with long cooling seasons. Conversely, homeowners in cold climates with long heating seasons should focus on HSPF ratings.

Electric heat pump efficiency ratings are important, but high ratings don’t guarantee superior performance. Heating efficiency is affected by several other factors:

• Energy source

• Climate

• Size

• Insulation

• Ductwork

Different types of heat pumps transfer heat energy from specific sources, influencing their efficiency. Air-source heat pumps effectively transfer heat between indoor and outdoor air, but ground-source and water-source heat pumps move heat more efficiently between indoor air and the ground or bodies of water.

How a heat pump works in winter is a common curiosity. Although heat pumps can operate in cold weather, climate specifically affects air-source heat pumps that transfer heat from the environment. Heat pumps in regions with average low temperatures above 40°F use less energy and don’t work as hard as heat pumps in freezing temperatures.

Home size determines heat pump size. Smaller homes require small-capacity heat pumps, and larger homes require large-capacity heat pumps. Improperly sized heat pumps heat and cool ineffectively, incur more wear and tear and have shorter lifespans.

The quality and amount of insulation in a home affect how much heat is retained and how often the heat pump runs. A heat pump will run more often if a home is poorly insulated with drafty windows and doors.

Ducted heat pumps are convenient, but ductwork detracts from the heat pump’s efficiency. Holes and poor connections lose heat and force heat pumps to run longer. Sealing the ducts improves efficiency, but badly deteriorated ductwork has to be replaced, increasing installation and labor costs.

A heat pumps’ HSPF rating measures its heating efficiency. The heating season performance factor represents the heat output in BTUs compared to the energy input in watt-hours over an average heating season. Heat pumps with higher HSPF ratings use less energy and have lower operating costs, less environmental impact, and better temperature and humidity control than units with lower HSPF ratings.

HSPF ratings are primarily relevant to consumers with substantial heating needs in cold climates. Cold climate heat pumps with high HSPF ratings and dual fuel heat pumps with furnaces are excellent options for cold regions. Consumers in moderate and hot temperatures don’t require highly efficient heating and should focus on cooling efficiency represented by SEER ratings. Alternatively, consumers comparing geothermal heat pumps should hone in on COP ratings.  

Several factors besides HSPF should be considered for optimal efficiency. The heat pump’s energy source, the regional climate, and the home’s size, insulation, and ductwork can detract from the heat pump’s efficiency.