Checking electricity consumption and seasonal performance factor (SPF) yourself

Whether your heat pump is running well is revealed by a single number: the seasonal performance factor (SPF). Why two meters are needed for this and when you should look at them in the first year is explained in the article After installation. This is about the practical side: where you read the meters, how you calculate, which errors creep in and what you compare the result with.

What the seasonal performance factor (SPF) tells you

klimaaktiv defines the seasonal performance factor (JAZ) as the ratio of the heat generated in a year for heating and hot water to the electricity used for it. A JAZ of 4 means: 1 kWh of electricity is turned into 4 kWh of heat, 3 kWh of which come from the environment.

Not to be confused with the figures in the brochure:

COP (coefficient of performance) applies to a single, specified operating state.
According to klimaaktiv, SCOP is a comparative value under standardised conditions and with a standardised climate.
JAZ measures what your system actually achieves in your house over the year.

klimaaktiv compares this to a car: the COP is the consumption on the test bench, the JAZ is the actual consumption. The values can differ significantly.

Step 1: Finding the meters

Heat meter. It measures the heat that goes into the heating and hot water. The klimaaktiv guide states that it does not need to be calibrated and can be omitted if the heat pump records the amount of heat itself. With many devices, you will therefore find the value in the control system menu, often under terms such as heat quantity, energy or statistics. Check whether heating and hot water are displayed separately. For the JAZ, you need the total.

Electricity meter. Ideally, you should have a separate meter just for the heat pump. The guide provides for a separate electricity meter to check the JAZ, unless the heat pump already records the consumption itself. If the system has its own metering point with the grid operator, that is your value. Some control systems also display their own power consumption. Ask the installer what exactly this value includes before you rely on it.

Smart meter. You can view 15-minute values for your grid connection in your grid operator's customer portal if 15-minute metering is active. According to E-Control, you can usually activate this yourself there. For the JAZ, this only helps if the heat pump has its own metering point. On the household meter, its consumption is mixed in with everything else.

Step 2: Read regularly

Create a simple list, on paper or in a spreadsheet:

Date
Heat meter reading (kWh)
Heat pump electricity meter reading (kWh)
Outdoor temperature, rough estimate

Once a month is enough, always on the same day. If you take weekly readings in winter, you will see changes more quickly after adjusting the heating curve.

Step 3: Calculate

The formula is simple:

JAZ = heat generated ÷ electricity consumed (both in the same period)

Example over one year (fictional values for illustration purposes):

Heat meter on 1 October: 12.400 kWh, one year later: 26.800 kWh. Heat generated: 26.800 − 12.400 = 14.400 kWh
Electricity meter on 1 October: 3.150 kWh, one year later: 6.750 kWh. Electricity consumed: 6.750 − 3.150 = 3.600 kWh
JAZ: 14.400 ÷ 3.600 = 4,0

Example for a winter month (also fictional):

Heat in January: 2.900 kWh, electricity in January: 900 kWh
Performance factor in January: 2.900 ÷ 900 = around 3,2

The monthly value in winter is almost always below the annual value. When it is cold, the heat pump has to work harder, and with an air-source heat pump, defrosting is also required. A weak January on its own is therefore no reason to worry. The entire year is what matters.

Step 4: Avoid typical mistakes

Unequal time periods. Heat and electricity must be read on the same day.
Forgetting hot water. If only the heating energy is counted, but the electricity also includes hot water, the JAZ will be too low.
The heating element. Many systems have an electric heating element as a backup. If it is connected to the same electricity meter, its consumption must be included in an honest calculation. If it kicks in often, this will significantly lower the JAZ. Ask the installer where you can read its operating time.
The first year. Drying screed after a new build or adjustments after commissioning distort the values. The second year is usually more meaningful.

Step 5: Compare with the planning

According to the klimaaktiv guide, the seasonal performance factor should already be calculated in the planning stage and enclosed with the documentation. For the overall system, the guide sets a target value of at least 4. However, it adds a caveat: in very well-insulated houses close to the passive house standard, hot water makes up a large proportion, meaning a JAZ of over 4 for heating and hot water is difficult to achieve without a solar thermal system. Look for the planned value in your documents. It is your most important benchmark because it was calculated specifically for your house.

For a rough classification, klimaaktiv states:

In practice, JAZs of between 3 and 4,5 are achievable for heating and hot water.
Optimised systems in detached houses achieve up to 5 for heating operation.
A JAZ of at least 3 should always be aimed for.

klimaaktiv also demonstrates how much money this makes: with a JAZ of 4 instead of 3, annual electricity costs fall by a quarter for the same investment. You can play through what this means for your heating costs in the cost comparison.

If the figure is not right

If your JAZ is significantly below the planned value, proceed step by step: first the heating curve, then the question of hydraulic balancing, then the hot water temperature. The order and the reasons for this are explained in the article After installation. If the system switches on and off unusually often, the article Is the heat pump running constantly? will help.

If the figure remains poor, take your list to the installer. Having readings over several months makes it easier to have an objective discussion.