When it comes to heating devices, there is no single specification more important than the HSPF rating. HSPF rating is the key metric for all heating devices; be it heat pumps, furnaces, or water heaters. Understanding it gives you the fundamental insight in all heating devices.
In fact, it’s so important that every larger heating device – below is an example of a mini-split heat pump – is required by law to include the HSPF rating:
HSPF stands for ‘Heating Seasonal Performance Factor’. It is a metric that determines the overall energy-efficiency of heating devices in much the same way as SEER rating for cooling devices.
In simplified terms, it gives you an idea of how significantly will running such a heat pump impact your electricity bill. You can be looking at several $100 savings every heating season with a high HSPF rating heat pump.
AHRI defines HSPF as:
The total space heating required during the space heating season, expressed in BTU’s, divided by the total electrical energy consumed by the heat pump system during the same season, expressed in watt-hours.
Basically, the HSPF rating tells us how much heating effect (in BTU’s) we will get per kilowatt-hour (kWh). Here are two practical examples:
- Heat pump with 8 HSPF will give us 8 BTU’s of heat for every kWh.
- Heat pump with 10 HSPF will give us 10 BTU’s of heat for every kWh.
Obviously, it’s much better to have a heat pump with a higher HSPF rating (in this case 10). Such a heating device will draw less energy for the same heating effect and you will pay less in heating expenses. You can check out a list of the best mini-split heat pumps with the highest HSPF rating here.
In the following article, we will answer:
- How is the HSPF rating calculated?
- What is a good HSPF rating for heat pumps?
- How much electrical bill savings per season can you generate by choosing a device with a higher HSPF rating?
In the end, we made some calculations regarding the classic problem of “I know 10 HSPF heat pump is better than 8 HSPF heat pump but 10 HSPF costs $3,000 and 8 HSPF costs $2,000.”
How Is HSPF Rating Calculated
To understand it fully, we need to know how the HSPF rating is calculated. HSPF is a metric of energy-efficiency, measured throughout the winter heating season. Every winter, we can measure:
- Electricity we spend on heating; the power use in kilowatt-hours.
- Heating effect we get; the heating capacity in BTUs.
Example: To heat out 1500 sq ft home during the 3-winter months (December, January, February), we spent 20,000 kWh. The heat pump powered by these kilowatt-hours produced a total of 160,000,000 BTU of heating effect.
Based on this, we can calculate the HSPF rating like this:
HSPF = Heating Effect (in BTU) / Electricity Spent (in Wh)
Be aware that we have to use watt-hours, not kilowatt-hours. The conversion is simple enough; 1 kWh = 1,000 Wh. If you use the numbers in our example, we get:
HSPF = 160,000,000 BTU / 20,000,000 Wh = 8
In short, the HSPF rating of such a heater is 8. How much did we spend on electricity? The US average price per kWh is $0.1319. We needed 20,000 kWh to warm our house. That comes to $0.1319 x 20,000 = $2,638 per heating season.
How much would we save if we used 10 HSPF units instead of 8 HSPF? In the case of 10 HSPF, we would have to use only 16,000 kWh instead of 20,000 kWh (8 HSPF). That would cost us $2,110.
Here is a quick summary of heating costs:
- HSPF 8 = $2,638 per heating season in electricity costs.
- HSPF 10 = $2,110 per heating season in electricity costs.
You can see that (in our example) higher HSPF 10 device produced $500 fewer electricity costs than lower HSPF 8 device. That’s the true power of energy-efficient heating, and it leads us to this point:
What Is A Good HSPF Rating For Heat Pumps?
Having a heat pump with a high HSPF rating is crucial. But what is a good heat pump HSPF rating?
In the US, the minimum federal HSPF rating for all units is 7.7. To earn an ENERGY STAR label, a heat pump much achieve at least 8.5 HSPF (for mini-split heat pump systems) and 8.2 HSPF (single-phase heat pumps).
- 7.7 HSPF is the minimum.
- 8.5 HSPF is a good HSPF rating (earns an ENERGY STAR label).
- There are heat pumps with 10 HSPF, or even higher.
To give you an idea of what the difference in these HSPF ratings is in the electricity dollars, we made some calculations. Let’s say that a 7.7 HSPF heat pump would need $1,000 for heating. How much would the 8.5 and 10 HSPF heat pumps need? Here is the cost calculation:
- 7.7 HSPF = $1,000
- 8.5 HSPF = $906
- 10 HSPF = $770
As you can see, the 10 HSPF heat pump spends 23% less electricity for the same heating effect. In this case, that makes a $230 difference in favor of the 10 HSPF heat pump.
How Much Can You Save By Buying Heat Pump With Higher HSPF Rating?
Several people have posed the following question, or thereabout, “I know 10 HSPF heat pump is better than 8 HSPF heat pump but 10 HSPF costs $3,000 and 8 HSPF costs $2,000.”
Obviously, saving $1,000 seems like a good idea. But we need to be aware that a cost of any heat pump is comprised of:
Heat Pump (Total Cost) = Initial Cost Of Heat Pump + Electricity Costs
The real question is does the lower running electricity costs justify the higher initial cost of a high HSPF heat pump. Some of you have requested an HSPF calculation that could explain that (and we’ve prepared it).
But let’s first look at one common example of two similar devices:
- 3 ton (36,000 BTU) heat pump with 8 HSPF that costs $2,000.
- 3 ton (36,000 BTU) heat pump with 10 HSPF that costs $3,000.
In 10 years, which one will be more financially viable?
Let’s first presume that heating season lasts for 3 months and you run the heat pump for 8 h per day, yielding 1000 working hours per season. Let’s also use the US national average kWh price of $0.1319.
Both devices generate 36,000,000 BTU of heating power. Knowing the HSPF rating, we can calculate how many kWh of electricity they burn, using the following equation:
Electricity Spent = HSPF / Heating Capacity (BTU)
Here is how many kWh each device spends with the electricity dollar amount:
- 8 HSPF spends 4,500 kWh. Electricity cost: $593.55.
- 10 HSPF spends 3,600 kWh. Electricity cost: $474.84.
As you can see, every heating season a 10 HSPF heap pump uses $118.71 less electricity. In 10 years, that’s $1187.10. So, the initial +$1,000 is well worth the extra cost, especially knowing this is a fairly conservative estimate.