Mats Bengtsson

Business case for moving to a Fighter 2020 heat pump

Mats Bengtsson mib over the years

The most important heat pump comparison is the COP factor

When I compare heat pumps, I tend to first look at the COP-factor (how much energy you get out in relation to how much energy you need to put in), and then translate that to the COP curve (so it can be used together with the knowledge of the temperatures at your location).

The second most important comparison is the effect available in the heat pump

It can be argued this is the most important factor, since if the effect is way too low, you will have no possibility to create the heat needed, independent of what COP you have. This is true.

But the reason for me to state it in this order is that the differences of size within a series of heat pumps from the same vendor tend to make very small improvements to your investment, since the bigger sizes tend to have worse COP and higher prices, whereas finding vendors with higher COPs make a huge difference in saved energy.

The heat pump COP curve must be compared to temperatures at the current location

Different locations have different temperatures. Since the heat pump COP curve is different at different temperatures, you can only valuate what the effects of the curve mean for you by comparing it to the temperatures at your location.

Thus you need to have access also to temperature data. These are available in different ways, and it should be possible to find data for a location reasonably close to yours.

To simplify this kind of comparison, I have provided a simple form, doing basic calculations, and a form using daily temperature data to compare heat pump paybacks.

The COP curve and the temperature at location must be compared to the house energy need

A house demands energy to be kept warm. How much energy is needed is not easy to calculate. In general, it can be said that the need increases rather lineary with the temperature, so a normal statement is to say "x Watts per degree Celcius". For my house, used in the calculations below, I have an approximate curve calculated for the energy needed.

The needed heating water temperature might be a show stopper

If the house has originally been desgned for another heating system, and thus need water with higher temperatures than coming from the heat pump, the heat pump might not be able to heat the house, even if it delivers enough power. In that case, you need to make changes also to the radiators.

I find cost calculations are best done based on day to day values

Calculations on heat cost can be done in different ways. For example based on yearly COP figures at location from a vendor or test institute, or based on quarterly or monthly figures, or ...

There is a compromise to make. If calculations are to rough, they will miss a lot of factors. If they are too compliceted, it will be hard both to find the data and to make them. The best compromise I have found is calculating based on day to day values.

Calculating the best alternative should involve comparisons

The starting point in my case is a house with an existing electric heater and an existing air to water heat pump. Both of these devices are old, so there is better equipment on the market. But it turns out that exchanging them in a profitable way is hard as long as they are working.

The newer equipment is a lot better. But the cost associated with the investment to exchange them should be weighed against the additional savings that are done. Also, the cost for going to the best alternative should not be weighed only to the current situation, but also to the second best alternative. It turns out that the additional saving in each extra improvement step often has a decrease in gain and an additional associated cost compared to the previous step making it a lot less profitable.

A smaller heat pump can be more profitable than a bigger from the same model series

As an example I will compare three alternative heat pumps from NIBE (the Fighter 2020 series). In this case, most important calculations are done as comparisons to the alternatives themselves, instead of as comparisons to the existing situation. This gives other results than I would have expected from a quick thought:

Considering the price of the pumps, the safest alternative turns out to be the smallest one. Intentionally dimensioning the heat pump so that the electric heater will work a lot during cold winter days, but relying on those days are fewer than the days where the COP for that pump is having the advantage. And even then, the investment is not worth doing until the old heat pump breaks down.

If the heat pump is used also to heat tap water, the business case improve

The tap water that is to be heated in the house is both similar and different to the water used for the heating. In some cases the heating water might need some more heating than can be provided by a heat pump. However for the tap water, it is more than likely tha this will be the case (yoy might want the water heated fast, and you might want it warmer than the heat pump can achieve). A rough business case calculation based on current tap water heating energy needs reveals a possible good business case.


Never trade stocks without having tested your system. In fact, most trading systems are not profitable if tested over many stocks. Full story...

Do not invest in heating equipment without having compared the alternatives, not only to current situation, but also to each other. Full story...

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