When researching and comparing heat pumps, you’ll come across two efficiency ratings – HSPF and HSPF2. These acronyms stand for Heating Seasonal Performance Factor and Heating Seasonal Performance Factor 2. Both rates measure the efficiency of a heat pump but represent different testing standards. This causes confusion for homeowners trying to determine the most efficient heat pump to buy.
In this guide, we’ll cover the key differences between HSPF and HSPF2 ratings, what the numbers mean, how to convert between them, and recommendations on comparing heat pump efficiency using these metrics.
What is HSPF?
HSPF stands for Heating Seasonal Performance Factor. This rating measures the total heating output of a heat pump over an entire normal heating season, divided by the total electric energy input. The higher the HSPF, the more efficient the heat pump.
HSPF ratings are calculated based on standardized Department of Energy (DOE) testing that simulates normal climate and usage conditions in the US. Up until 2023, HSPF was the main efficiency rating used for heat pumps. Models produced and sold in the US must display their HSPF rating. Typical HSPF ratings range from 7 to 10 for air source heat pumps and 8 to 11 for geothermal (ground-source) heat pumps. The minimum HSPF for Energy Star-certified heat pumps is 8.2.
What is HSPF2?
HSPF2 is the new metric adopted by the DOE in 2023 to represent real-world efficiency and performance of heat pumps. HSPF2 testing better accounts for colder outdoor temperatures, part-load conditions, external pressure test conditions, and continuous fan settings.
The HSPF2 rating is calculated in the exact same way as HSPF – by dividing total heating output by total electric input over an entire simulated heating season. However, the testing conditions to determine those values are more stringent to better reflect how heat pumps perform in homes.
DOE testing shows HSPF2 ratings run approximately 11% lower than HSPF on average. So an HSPF 10 heat pump would likely have an HSPF2 of around 8.9.
HSPF vs HSPF2: Key Differences
Here are the 4 main differences between HSPF and HSPF2 testing that account for the lower HSPF2 efficiency ratings:
1. Colder Temperatures
The original HSPF test procedure only dropped the outdoor test temperature as low as 47°F, even though many parts of the country see extended periods with temperatures below freezing. HSPF2 lowers the minimum test temperature all the way down to 35°F. This better represents the heating load in cold regions during the winter.
Since heat pumps lose efficiency as the outdoor temperature decreases, accounting for these colder temperatures results in lower overall seasonal efficiency ratings under the HSPF2 test.
2. Part Load Conditions
The HSPF test procedure assumed the heat pump was operating at full capacity 100% of the time. But in most homes, the heating load varies throughout the day and season, meaning the heat pump frequently operates in part load conditions.
HSPF2 testing factors in a range of part load scenarios across different outdoor temperatures that better match how a heat pump performs in a real home. These part load conditions lower the overall seasonal efficiency versus assuming full capacity operation. Multi-stage and variable speed heat pumps achieve much higher HSPF2 ratings by operating at longer cycles, at reduced energy consumption.
3. Continuous Fan
Original HSPF testing cycled the indoor fan on and off with the heating demand. However, most modern heat pumps are installed with a continuous fan setting for increased comfort and air circulation.
The HSPF2 test runs the indoor fan continuously during the heating operation. While this increases comfort, it also slightly decreases efficiency compared to an intermittent fan. The continuous fan operation further reduces ratings versus HSPF.
4. External Pressure Test Condition
HSPF2 introduces an external static pressure of 0.5 inches of water column during testing. This simulates the added resistance of real-world duct systems, air filters, etc. The higher external pressure, the higher the electric consumption of the blower will be, which will result in lower efficiency. A properly designed/sized duct system is key to maintaining peak efficiencies.
By factoring in these four key differences compared to HSPF, the new HSPF2 rating provides a much more accurate prediction of how a heat pump will perform once installed in a home under normal operating conditions.
Converting HSPF to HSPF2
Since both ratings represent the same overall calculation of heating output divided by electric input, you can convert between HSPF and HSPF2 using a simple ratio:
HSPF2 = HSPF x 0.89
Here are some examples of converting HSPF to HSPF2 using that formula:
- HSPF 8 = HSPF2 7.1
- HSPF 10 = HSPF2 8.9
- HSPF 12 = HSPF2 10.7
So, if you know the HSPF rating for a heat pump, multiply it by 0.89 to estimate the HSPF2 rating. This provides reasonable guidance to compare efficiency between units rated with either metric. Keep in mind that an older heat pump system’s HSPF rating has probably lessened over time due to age, wear and tear.
Comparing Heat Pump Efficiency
When researching and selecting a new heat pump, follow these key recommendations to evaluate and compare efficiency between different models accurately:
- For older models only rated in HSPF, take the time to convert to an estimated HSPF2 rating using the 0.89 conversion formula. This will provide a more realistic expectation of true efficiency versus the potentially inflated HSPF rating.
- Give strong preference to models that voluntarily provide both HSPF and HSPF2 ratings from the manufacturer. This demonstrates the manufacturer is committed to full transparency when it comes to efficiency ratings.
- Whenever possible, compare specifications using the HSPF2 ratings rather than HSPF. HSPF2 better reflects real-world efficiency, while HSPF tends to overestimate performance under ideal conditions. However, you can still make reasonable comparisons using the conversion formula when only HSPF is available.
- Verify that any heat pump under consideration meets the Energy Star minimum requirement of an HSPF2 rating of at least 7.5. This should be used as the absolute baseline – do not consider any units with lower HSPF2 ratings.
- For optimal efficiency, look for models that achieve HSPF2 ratings of 9.0 or greater. While cost typically increases with efficiency, utility bill savings over time can justify the larger upfront investment.
- Do not neglect to also evaluate heating capacity specs. Efficiency ratings only assess the ratio of output to input, not the total heating capacity at a given outdoor temperature. Make sure to choose a heat pump appropriately sized for your climate and home’s heating needs.
- Carefully compare warranties between different brands and models. Look for at least a 10-year warranty on the compressor and parts as a proxy for expected reliability and longevity.
Using this guidance when researching will allow you to see through the confusion of HSPF vs. HSPF2 ratings. Focus your comparisons on real-world HSPF2 specs, properly convert from HSPF when needed, and choose a model that balances efficiency, capacity, and warranties.
The Logan Difference
When you choose Logan Heating & Cooling for your heat pump installation, you get the expertise of a family-owned, local company that cares about doing the job right.
Our experienced installers go through extensive training to ensure quality workmanship. We also take steps to avoid frustrations – having all needed equipment and materials on hand before the installers arrive so there are no delays.
Throughout the process, we emphasize communication. Installers follow a checklist that gets signed off by experienced managers. We also do a thorough walkthrough when finished, demonstrating the system and thermostat operation and recommended maintenance to keep the new system operating at peak performance.
Our team helps ensure your warranty is valid and won’t fall back on the customer. We stand behind our work and want you to have the best possible experience.
In addition, Logan Heating & Cooling gives back to the community through donations, giveaways, and helping friends and neighbors. You get great service while supporting a local business committed to your satisfaction.
Frequently Asked Questions
What is a good HSPF2 rating?
Look for models with an HSPF2 rating of at least 8. The highest efficiency heat pumps exceed 9 HSPF2.
What was the minimum HSPF before 2023?
The minimum HSPF rating was 8.2 before the switch to HSPF2. The lowest rating you should consider is 7.5 HSPF2.
How do I know if a rating is HSPF or HSPF2?
If the testing and model year was before 2023, it is HSPF. Any ratings for 2023 or later models will be HSPF2. Contact the manufacturer if uncertain.
Do ductless mini-splits use HSPF or HSPF2?
Ductless mini-split heat pumps have used an HSPF2 equivalent rating for several years. But you may still find models rated in HSPF. Compare HSFP ratings if available or convert HSPF to HSPF2.
Which is more important – HSPF or SEER?
Focus first on HSPF or HSPF2 since it reflects winter heating efficiency. SEER rates summer cooling efficiency. Get the highest ratings within your budget for both.
Can I convert SEER to SEER2 as well?
Yes, SEER2 uses the same 0.89 conversion ratio. SEER2 better reflects real-world cooling energy efficiency rating compared to the older SEER metric.
Understanding the move from HSPF to the more representative HSPF2 rating will help you make the most informed decision when purchasing your next heat pump. Consult this guide to cut through the hype and identify truly efficient models that perform as advertised.
