Which heating is recommended for KfW 55?

Hello! We are currently planning a house and, since you don’t do that very often, we have many questions. Due to the development plan of our plot, we are required to build a KFW 55 house and are now unsure what type of heating we need. House building companies say different things! Is it possible to install a normal gas condensing boiler in combination with solar water heating, or do you have to use geothermal or air heat pumps? I am grateful for any answer!

Hello,

We are forced to build a KfW 55 house due to the development plan of our property

Take another close look, I honestly can’t imagine that; KfW 70 yes, that corresponds to today’s standard, but KfW 55? I’m also not sure that the municipality is allowed to do that, unless you have chosen a property in an area that is meant to have a signal character.

Is it possible to install a normal gas condensing boiler in combination with solar water heating, or do you have to use geothermal or air heat pumps?

In which direction do you want to go, prefabricated or solid house?

Best regards

Hello construction expert,

we ACTUALLY HAVE to build to KFW 55 standard, but we knew that when we bought the plot. Well, now we are struggling with various construction companies and one says we can achieve it with geothermal energy, another says air heat exchangers, and others think a gas boiler will do since our building envelope is extremely tight and insulated. We want to build solidly (prefabricated houses are equally fine) and are now not exactly sure how we can achieve this standard. It all gets quite expensive (extra insulation everywhere, different windows, ventilation system... etc). So, what should we choose now? Geothermal energy (only possible with deep drilling, as the plot is too small) is expensive. We are standing there like a deer in headlights!
Best regards!

Hello Amazingbee

The topic of heating in a new building is not only difficult to answer for a KfW 55 house. Theoretically, you can meet the requirements with all heating systems. It does not only depend on the heating system, but on the overall package. The combination of heating, insulation, etc. must be right.

Unfortunately, many providers seem to make quite curious calculations, i.e. apparently many heating systems are incorrectly sized...

In my opinion, the most important question initially is which energy source you want to depend on in the long term? You need heating oil (which is nowadays out of the question), gas, or electricity to heat your apartment.

Then you have to know the heat energy demand of your house. Now you can calculate how much primary energy you need from that: Example: With a heat pump with an annual performance factor of 4, you need 25W of electricity for 100W of heat.

Now you can already compare the different heating systems based on their primary energy demand – this is probably decisive for the KfW calculation...

To be able to decide on a heating system now, you also have to consider which "fuel" costs (gas or electricity costs) you will have per year. It only becomes difficult at the point where you have to think about how the price development will probably look in the coming years.

In my opinion, the gas price will rise more strongly than the electricity price in the next few years – i.e. the operating costs of the gas system will probably be significantly higher in relation to the heat pump. If you add up the operating costs (including maintenance, chimney sweep, etc.) that arise during the lifetime of the heating system (which is calculated at 20 years) and add the purchase costs of the heating system (these are significantly higher for a heat pump than for a gas condensing boiler), then you might find it easier to make a decision...

Unfortunately, this calculation is very much dependent on the price development of electricity and gas – and no one can really predict this...

My very personal opinion is that today – especially with a new building (even more so with KfW 55) – I would definitely not rely on gas anymore – but I can be wrong. We will see in 20 years.

Hope I was able to help you

Best regards from the Ruhr area Micha

Hello,

Hello Building Expert,

we ACTUALLY HAVE TO build KFW 55 ... We want to build solid (a prefabricated house is just as okay) and now don't know exactly how we can achieve this standard. Because that's all quite expensive (extra insulation everywhere, different windows, ventilation system... etc.). Well, what should we choose now? Geothermal energy (only possible with deep drilling because the plot is too small) is expensive. So we're standing there like a deer in headlights!

So different windows is nonsense - who told you that rubbish? If you want to build solid, you have to accept thicker masonry - 42.5 monolithic or 44.5 with ETICS, but this reduces the living space by about 6.0 or 8.0 cm all around on every level. Then usually more expensive technology has to be installed with the first stone size, e.g. an integral system - consisting of an air-to-water heat pump, controlled ventilation with heat recovery. With this, however, you buy into the disadvantage that your utility room loses significant space, as these systems take up about 2.0 sqm of wall area and also protrude about 80 cm into the room from the wall. These systems generally cannot be installed in the basement unless the basement is at least 1.0 m above ground; this system must realize counterflow supply and exhaust air!

With the second stone size, it strongly depends on the location of the plot; if it is good (few windows facing north etc.) it might be possible that an air-to-water heat pump along with decentralized ventilation achieves the desired standard. Here, the structural engineer or building services planner should calculate very precisely!

But however you decide, KfW 55 means an additional cost for the building project in the range of EUR 20-25 thousand depending on house size for 42.5 masonry and EUR 15-20 thousand for 44.5 with ETICS, again depending on house size.

Kind regards

Hello!

It is indeed the case that a KfW Efficiency House 55 is technically associated with greater effort and higher investment costs. If the development plan requires such a construction method, then it is definitely necessary to invest this additional amount.

Those who do not necessarily have to build an efficiency house according to KfW criteria have a good solution with an energy-saving, well-insulated building envelope and simple heating technology (affordable gas condensing boiler or air-water heat pump) and an efficient residential ventilation system. The technical setup for a solar system generally does not pay off in the long term either.

Regards

T.H.