Convert HSPF To COP: Calculating COP From HSPF Rating (Heat Pumps)

The energy efficiency of heat pumps is expressed in COP (Coefficient Of Performance). On the heat pump’s specs sheets and EnergyGuide labels, however, you will only see HSPF (Heating Seasonal Performance Factor). Because HSPF directly depends on COP, we can easily convert HSPF to COP.

Below, you will find these two very useful resources if you want to convert the HSPF rating to COP:

1. HSPF to COP calculator. You simply input the HSPF rating and the calculator will tell you what the COP value is.
2. HSPF to COP chart. A calculated table for HSPF to COP conversions ranging from 5 HSPF to 15 HSPF (from 1.47 COP to 4.39 COP).

Let’s get a grip on what we are converting first:

COP or Coefficient of Performance is an all-encompassing metric for heat pumps. It tells you the potential efficiency a heat pump could have at a certain outdoor-indoor temperature differential:

COP_{heat pump} = T_hot/(T_hot-T_cold)

As you can see, it depends on indoor and outdoor temperature (in HVAC terms, we talk about wet bulb and dry bulb temperatures).

Compared to COP, HSPF is a more practical way of expressing heat pump efficiency. While the COP value includes various temperatures, the HSPF, on the other hand, will tell you how much useful heat can a heat pump output per certain power input at a specific outdoor-indoor temperature differential.

Example of HSPF to COP conversion: Let’s say that a heat pump has an HSPF rating of 10.0 at 47°F. What is the COP at that temperature? COP at 10 HSPF rating is 2.93. That means that the heat pump has 293% efficiency.

To convert HSPF to COP, we can use two equations:

• Exact HSPF to COP equation (complex one) is used by HVAC engineers designing heat pumps.
• Approximate HSPF to COP equation (simple one) is used by pretty much everybody else, from HVAC guys to homeowners just wanting to compare COP values of different heat pumps.

Here are both of these formulas:

Exact equation: COP = -0.026 × HSPF² + 0.624 × HSPF

Approximate equation: COP = 0.293 × HSPF

For most intents and purposes, we will use the simple approximate equation to convert HSPF to COP. You can quite easily see that 1 HSPF is equal to 2.93 COP from the equation.

Example: What is the COP of 8 HSPF rated heat pump?

We just use the conversion equation like this:

COP (8 HSPF) = 0.293 × 8 = 2.34

This is just one example. To help everybody out, we have developed a neat HSPF to COP calculator that you can freely use. Below the calculator, you will also find an HSPF to COP conversion chart for HSPF ranging from 5 to 15 (converted to 1.47 COP to 4.39 COP):

HSPF To COP Calculator

Here is how you can use this calculator to convert the heating seasonal performance factor to the coefficient of performance:

Let’s say that we have a very energy-efficient heat pump with a 12.0 HSPF rating (as found on the EnergyGuide label). What is the COP? Just slide the slider in the calculator to ’12’ and you get the result: 3.52 COP.

You can check the HSPF to COP calculated table here:

HSPF To COP Chart

As you can see, it is not all that difficult to convert HSPF to COP.

Regarding COP and HSPF rating at low temperatures: At very low temperatures (single-digit, below zero), you will see HSPF rating fall below 4 and COP value fall below 1. In recent years, we are seeing a rise of cold climate heat pumps (CCHP) that can achieve 125% efficiency even at -15°F. You can check the best heat pumps for cold weather currently on the market here.

If you have any troubles converting HSPF to COP, you can use the comment section below and we will try to help you out with the calculation.