Mats Bengtsson

Knowing how much more efficient heating heating alterantives are

Mats Bengtsson mib over the years

What changes to prioritize

There are many things to do in order to make heating more energy efficient. The hard question to answer is which of those routes that best saves energy and money.

My belief is to always try to do the thing that in the current situation that gives the best result considering the effort spent. This means that depending on the house and the current isolation and the current heating equipment, what is best to do will vary over time.

The worse the current situation, the easier it is to guess if something will give a payback or not. For example, if the house is heated only by a furnace, with no types of heat pumps involved, then there is a good chance that some kind of heat pump will save money. But if you already have some kind of heat pump, it becomes quite difficult to answer the question if a better or stronger heat pump will be an economical investment or not.

In the same way, if the attic has 5 centimeter thick isolation, a good guess would be that an additional 40 centimeters would save a lot of energy. But if the isolation is already 40 centimeters, what is the best route to take?

You need to know the amount of energy needed to heat the house

In order to be able to make any good judgements of the savings of changes to the heating or isolation, you need to know what amount of energy is needed for the house. Already this is an abstacle, since there is no easy way to measure and estimate this accurately. But if you accept that what you can do is to make estimates, even if not to understand the exact truth, you can easily get quite far. Educated estimates will quickly help you a long way on the road, and make the comparisons quite possible. Just as was mentioned above, the better the heating and isolation you already have, the better estimates you need to use.

For example look at the stepwise improvements below:

  • Only knowing the total energy used in your house is at least allowing you to see the maximum size of yearly cost reduction
  • Knowing what part of the total energy used in your house that is used for heating allows you to even better estimate the maximum size of yearly cost reduction. It also allow you to compare your heating as well as household energy consumption with others with similarly sized houses and houeseholds. Thus also to understand what of the two parts that is relatively least efficient today
  • Comparing the energy consumption above to the average outside temperature for the same time allows you to compare heat needs over the years. This means that heat usage can be compared between years with different temperatures, which is otherwise very hard considering the huge differences during warm and cold years.
  • Translating the part of the energy used for producing the heat to energy really added to your house allows you to understand how much improvement is already coming from your existing heat pumps and similar, if any

Thus, frequently looking at both your energy consumption and the average outside temperature for that time will quickly give you a picture of how much energy is needed depending on the outside temperature, and allow you to estimate what savings could be achieved by different measures.

Knowing the heating needs, you will see huge differences compared to simpler guesses

The knowledge brought in through the simple examples above (average outside temperature and corresponding heat respectively electricity consumption) quickly gets you pass the rough estimates used by advertisements, and allows you to get much more true pictures of what can be achieved.

For example, we know quite well what heating is needed at different temperatures (hot water excluded). We also know quite well how that heat is divided between the electric heater and the heat pump. We also have available decades of average mean outside temperatures for locations around us. Using that information, we can compare different alternatives with acceptable accuracy, and include the effects of temperature swings. We can even understand what happens if the mean temperature increases and decreases with say a degree or two.

Those calculations lead to interesting conclusions that would have been hard to guess. Most importantly, the best profit with a heat pump is not neccessarily for the heat pump replacing most of the electric heater. This, due to the fact that a large heat pump might have a worse COP-diagram than the smaller pump.

The difference in saving is huge compared to simple web page estimates

For example I can illustrate the calculation difference through the use of a web page from one of the many vendors as example (NIBE). And this example is actually an example form one vendor asking more questions than most vendors, many vendors will state your saving without knowing if you have a bath tub, are a small or large family, have a house in the south or the north, ... Using NIBEs link I get to a page where I can see how much I can profit from using their heat pumps. They only need a few figures to state the savings:

  • Where my house is located (presumably to understand yearly temperatures)
  • When my house was built or totally renovated (presumably to understand how well isolated it is)
  • Number of persons in household and if we have bath or shower (presumably to guess yearly warm water consumption)
  • Amount of energy used for heating respectively for household (it seems from their examples fair to guess that warm water is to be excluded from household)

After this I get to know that I can save in the neighbourhood of 12000 KWH per year with a warm water heat pump (out of the about 19000 KWH I have assumed is for heating plus warm water). But this estimate is so rough, that it does not give anything:

  1. They do not ask if there is already any kind of heating involved not being direct electricity (heat pump or sun panels). So the calculation becomes unusable from that omission only
  2. The amount of heat used for heating warm water is based on their side on an assumption based on something, but in order for me to put my figures in, I have to base the figure on something as well. Since I never is asked how I got to the figure, and they never explain what figures they used on their part, the uncertaininties becomes so huge, that they can not be used for calculations.
  3. Since the saving is stated, but not the solution and investment needed to reach it, it can not be included in a business case. Thus, I do not know if the saving will be realised within 5 years or 50 years. In the latter case, I might be less interested.


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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