HSPF is heating seasonal performance factor. That’s what the letters stand for. But what is HSPF and what does it mean for your heat pump? What is a good HSPF rating?
This guide to heating seasonal performance factor or HSPF explains this efficiency measurement and how to choose a heat pump with the right HSPF for your needs.
What is HSPF?
Heating seasonal performance factor is a measurement of how efficiently an air source heat pump gathers and moves heat from one place to another.
What’s an air source heat pump? There are two basic heat pump types. A geothermal heat pump gathers heat in winter from the earth or water and dumps heat there in summer.
An air source heat pump gathers heat from outside air in winter and releases it into the air in summer.
Measuring HSPF Rating: HSPF and BTU
HSPF or heating seasonal performance factor is a measurement of how efficiently the heat pump uses electricity to capture BTUs of heat and bring them into your home in winter.
There are two efficiency measurements for air conditioning efficiency, that is, the cooling mode of a heat pump or air conditioner. The first is SEER, or seasonal energy efficiency ratio. We discuss it here.
The second is EER, or energy efficiency ratio. We’ve covered that measurement in this guide.
If you’re interested, the efficiency measurement for gas furnaces, oil furnaces and boilers is called AFUE, annual fuel utilization efficiency. We’ve covered AFUE in this guide.
Now, back to HSPF. The more efficiently a heat pump collects and moves BTUs of heat in winter, the higher the HSPF rating. Think of it like gas mileage – miles per gallon is exactly like HSPF rating, the BTUs moved per electricity used. And that’s how HSPF rating is determined.
Heat Pump Sizes and HSPF
BTU stands for British thermal units. Each BTU is a tiny amount of heat. Heat pump capacity is measured in BTU/hour – the number of BTUs that can be moved each hour.
Standard split system heat pumps range in size from 18,000 BTUs to 60,000 BTUs. In the industry, these terms are also called 1.5 tons and 5 tons – each “ton” being 12,000 BTUs.
Common heat pump sizes are 18K, 24K, 32K, 36K, 42K, 48K and 60K, with K equaling 1,000 BTUs.
Mini split or ductless heat pumps start at about 6,000 BTUs and range to 48,000, though some larger models are available. There are many common sizes, so choosing one ideally suited to your heating and air conditioning needs is easy.
Heat Pump Size and Efficiency
You’ll notice when you shop for heat pumps that they list efficiency as “Up to 9.5 HSPF” for example. It’s always “Up to.” This means that the most efficient size, usually one of the smaller sizes, reaches that efficiency, but larger units do not. For example, consider the Rheem RP17 heat pump. It’s available in 24K, 36K, 48K and 60K sizes. The 24K unit has a 9.5 HSPF rating, but the rating for the three larger sizes is just 8.5 HSPF. That’s a common scenario.
Heat Pumps and Electricity – What’s the Connection?
The amazing thing about heat pumps is that they don’t create heat using fossil fuels like a furnace burning natural gas, or through electric resistance like a space heater.
Instead, they use a small amount of electricity to circulate refrigerant, and the refrigerant aka freon, pumps heat, hence the name of the equipment – a heat pump.
HSPF – How Efficient Is a Heat Pump?
Some of this is technical. If you’re not interested, you might want to skip down to the next section on “what’s a good HSPF?”
That section discusses how efficient your heat pump should be based on your climate and other factors. It’s not one-size-fits-all, and just saying “buy the highest HSPF heat pump you can afford” isn’t always a cost-effective choice.
OK, here’s an interesting way to measure the “gas mileage” or HSPF of a heat pump: COP, or coefficient of performance.
COP measures how much heat gets moved vs. the amount of electricity used. To determine the number, we multiply the heating seasonal performance factor of a heat pump times .293, a number we get using this equation for COP:
Avg COP = Heat transferred / electrical energy supplied
The equation is Avg COP = (HSPF x 1055.056 J/BTU) / (3600 J/watt-hour) = 0.29307111 HSPF
J stands for Joules, a measurement of heat.
A space heater uses electric resistance heat. It has a COP of 1 – it delivers a 1:1 ratio of electricity used to heat produced. A space heater HSPF rating is 3.41 – every inefficient.
HSPF in today’s heat pumps ranges from 8 to 13.
A heat pump with an 8 HSPF rating moves 2.34 times as much heat energy as the electricity used.
Here are common HSPF ratings and their COP:
- 8 HSPF = 2.34 COP
- 9 HSPF = 2.64 COP
- 10 HSPF = 2.93 COP
- 11 HSPF = 3.22 COP
- 13 HSPF = 3.8 COP
What Is a Good HSPF Rating?
The higher the HSPF, the more efficient the heat pump is.
So, it stands to reason that the colder your winters are, the higher your HSPF should be.
In our Heat Pump Reviews and Prices Guide, we have a section called What Heat Pump Efficiency is Right for You.
To summarize, here are our recommendations – our answer to “what is a good HSPF rating?”:
8.0 to 8.5 HSPF is a good HSPF rating for the mildest parts of Zones 3 & 4
8.5 to 9.5 HSPF is a good rating for most areas in Zones 3, 4 & 5
9.6 HSPF and more efficient heat pumps are bet for Zones 1 & 2, and if the unit is designed for cold climates too, then Zones 6 & 8
Why wouldn’t you choose the most efficient heat pump no matter where you live?
Well, if your goal is the most eco-friendly heating possible, then sure, you should buy the most efficient model you can afford.
However, if being cost-effective is your goal, then matching the efficiency to the climate makes more sense. Here’s why:
Heat pump prices:
- 8.0 to 8.5 HSPF heat pumps installed: $2,700 to $4,400 based on size and performance.
- 8.5 to 9.5 HSPF heat pumps installed: $3,800 to $6,000 based on size and performance.
- 9.6 to 13.0 HSPF heat pumps installed: 5,000 - $8,500 or more based on size and performance.
So you can see that efficiency costs money. In a very warm / very cold climate where your monthly energy bills are high, it makes sense to reduce them where you can. If you pay $1,600 more for a 9.5 HSPF heat pump compared to an 8.5 HSPF model, how long would it take you to make up the money through lower energy bills? If you saved $25 per month, which is reasonable, it would take you 64 months of heating and cooling. If your heat pump runs 9 months of the year, either heating or air conditioning, it would take about 7 years to recoup the extra money.
It would take much longer to make your money back if you bought a top-dollar, most-efficient heat pump. Frankly, most homeowners don’t ever make their money back, even in climates with the most extreme weather.
Then why would you buy the most efficient heat pump?
People do it for two reasons. They are committed to green heating and air conditioning and/or they want the improved performance of a super-efficient model. And a third reason might be that sometimes people get sold something they don’t really need.
What do you mean by heat pump performance? Heat pumps are either single-stage (1-stage), two-stage (2-stage) or variable capacity (modulating, variable-speed).
Single-stage models run at full capacity and are least efficient. 2-stage heat pumps run on low or high, and they are in the middle of efficiency. Variable capacity heat pumps change capacity in tiny increments from about 40% to 100%. They are the most efficient. And they optimize indoor comfort through balanced temperatures and the best dehumidification in air conditioning mode. All have variable speed blowers that gradually ramp up and slow down, so you never feel a blast of untreated air (warm air in summer; cool air in winter).
1-stage heat pump efficiency: 7.7 to 9.0 HSPF
2-stage heat pump efficiency: 8.5 to 9.5 HSPF
Variable capacity heat pump efficiency: 9.2 to 10.0 HSPF for most, but there are a few like the Carrier Infinity 24 and identical Bryant Evolution Extreme 24 have an HSPF rating of 13.0. Rheem’s new RP20 heat pump offers 11.5 HSPF, which is also quite impressive.
How a Heat Pump Works
This section is a quick overview that will allow you to understand heat pumps and why efficiency is important.
The outside unit, called the condensing unit or heat pump, contains three critical components: A radiator-like coil, a compressor and a fan.
There’s also a coil inside – in your furnace or air handler or connected to it.
Refrigerant lines run between the coils to circulate refrigerant.
In Summer / AC Mode:
The compressor pumps refrigerant through one line to the indoor coil, called an evaporator coil.
In the evaporator coil the refrigerant expands, turning into a gas, and collecting heat – just like water evaporating from your skin cools it by taking heat away.
The hot refrigerant is pumped outside through the other line.
In the condensing coil outside, it is condensed back into a liquid, and the heat is squeezed out of it, so to speak.
The released heat radiates out of the coil and is dispersed with the help of the fan.
Indoors, as heat is removed from the air, it cools. The blower motor pushes the cooled air into your ducts while pulling in warm air to be cooled by removing heat.
The indoor coil gets cold, and moisture from the air condenses on it and is drained.
That’s how your indoor air gets cooler and more comfortable when your heat pump is in air conditioning mode.
In Winter / Heating Mode: The cycle is reversed with the use of a piece of equipment called a reversing valve. The refrigerant picks up heat outdoors and brings it inside, releasing it in the indoor coil where it is pushed into your ducts by the blower.
The more efficiently it can do this, the higher the HSPF rating. The keys to efficiency are an energy-efficient compressor and coil design that effectively dispenses heat.
Remember our other HVAC efficiency rating FAQ guides: