Which heating system is suitable for the new construction of a KfW 70 house

We are planning the construction of a Kfw 70 house and do not know what kind of heating system we should install.

Framework parameters:
Living area 150 sqm
Single-story, underfloor heating, electric shutters

Concept:
To be independent from gas or oil, we want to use an air-source heat pump (geothermal energy is considerably more expensive), plus solar thermal with about 6 sqm in an optimal south orientation, and we are also considering a water-driven wood stove to be able to heat with wood alone in an emergency.
Possibly also solar panels oriented west for energy generation (air-source heat pump and generally self-consumption).

Of course, the acquisition costs are quite considerable. With a "normal" calculation starting from today, the whole thing will take many years to pay off. If you take out a loan for this and have to repay it piece by piece (interest!). But we think that the raw material prices for gas and oil will increase immensely in the coming years. Also electricity, hence the additional panels for self-consumption.
Fortunately, due to an inheritance, we have enough cash to pay for the entire project in cash (no loan!). However, no one has been able to present us with a corresponding cost-benefit calculation so far. Does this make sense or are we just getting carried away here?

A builder friend advises installing a good gas heating system with solar thermal. The house is super insulated and that should be enough. Plus a simple wood stove and that’s it...

I would be interested in a few opinions here... The project might possibly start this year.

Thanks and best regards

Tom

So there are already quite a few questions and answers here regarding all the heating points.
Fireplace with water jacket? The control unit will be happy, as it also has to take some of the fireplace’s heating capacity and store it in the buffer tank.
Solar thermal? There are people who believe that it can really pay off - if you can accommodate a huge, fully insulated buffer tank in the basement. Probably not sensible in combination with an air-to-water heat pump.
Now add a central controlled residential ventilation system with heat recovery - and the control units will be happy.

The recommendations here in the area:
Recommendation 1: Gas condensing boiler + solar thermal.
Recommendation 2: Air-to-water heat pump + photovoltaic for own consumption.

The better the building envelope is insulated, the more likely an air-to-water heat pump makes sense.
Even more so with a proper ventilation system.

Depending on who you ask. The better insulated the house, the more an air-to-water heat pump makes sense.
Brine heat pump: depends on plot size whether it’s feasible or not. For the house I currently live in,
it would be hopeless. For the one I’m building, it might be possible but is still being calculated...

Regards
GrrIngo

Another idea: why only Kfw70 and not better insulation towards Passive House standard?

Our approach for a similar house (single-family home, 160 sqm living space, 1.5 stories, no basement, underfloor heating, perfect south orientation with large south-facing windows) looks like this:
- Exterior walls of Poroton T7 with integrated mineral wool insulation, 49 cm thick. You can google for information.
- Gas condensing boiler 6 kW for hot water and heating
- No solar thermal system, because including planning, installation, storage, pipes, control, etc., costs about 15,000 EUR, which never pays off with the low heating demand of the house. With the 15% rule because of the well-insulated exterior walls, you still get KFW funding.
- No central controlled residential ventilation with heat recovery, because it is about as expensive to purchase as a solar thermal system. Instead, we install the so-called "humidity-regulated residential ventilation" (just google it). The slightly increased heating demand due to the supply of unheated air in winter is about as expensive as the operating costs for central controlled residential ventilation with heat recovery – rather lower.
- No heat pump stuff. Very expensive to purchase (> 15,000 EUR) and might maybe pay off in 20 years. But then the pump will already be broken again. Personally, I also don’t like the noisy, ugly outdoor units and the seasonal performance factor considered good here in this country is, in my opinion, far too low. Overall, good lobbying has been done there.
- Leave space in the basement or utility room for retrofitting future technologies. A lot is happening with solar thermal systems, photovoltaics, heat pumps, etc. Maybe that will become interesting in 20–30 years and then you can install that stuff.

So we put a bit more money into good insulation. It is durable, has no operating costs, and reduces dependence on the price fluctuations of gas.

Regards
rw

Hello construction expert,

I am a private builder, planning a single-family house in Berlin with an architect and specialist engineers. I have already expressed my opinion on the topic of heating.

Regards
klblb

Hello,

We are planning the new construction of a Kfw 70 house and do not know what kind of heating system to install....

Similar questions have been asked here frequently. Just browse through the forum on this!

...Of course, the acquisition costs are quite considerable. With a "normal" calculation from today's day X, it takes many years for the whole thing to pay off.

Investments in the thermal quality of the building envelope or system technology are a substitution of future energy costs. The interest rate level is historically low; how the costs/kWh for each energy source will develop, no one knows. What is certain, however, is that they will mostly rise well above the general inflation rate.
If you want to evaluate the investment or the economic efficiency of technical solutions, the actual demand (performance, energy) for heating, hot water, and possibly ventilation must first be known. Everything else is guesswork or a look into a very murky crystal ball (clairvoyance)!
Tendentially: The higher the demand, the higher the investment, the greater also the claim regarding energy efficiency. The more sensible it is to also use free environmental energy.

...A builder friend advises installing a good gas heating system with solar thermal.

Whether that is really a friend, I would doubt ;-)

best regards

Hello,

if you look at the current energy prices, most comparisons show that over a period of 20-25 years, very similar total costs arise for gas, wood, and heat pumps due to the different investment and operating costs, only an oil heating system is usually estimated to have higher total costs. Therefore, the fundamental question here is whether you prefer lower acquisition costs or lower operating costs.
And here begins the rather tricky assessment of the individual case, because especially the performance of solar thermal energy, which can be used in combination with the gas condensing boiler or the air heat pump, as well as that of the solar cells for electricity generation, is very strongly dependent on the location and shading. However, the air heat pump is also influenced by the location.

I would definitely have a heating value and heating demand calculation prepared and accordingly create a cost comparison. Although this costs a little, investing a bit more in planning is rarely a mistake.
And then I would carry out the mentioned total cost comparison over 20-25 years. If significant differences appear here, you already have a good basis for decision-making; if it remains close, as is often the case, you should consider whether you prefer a heating system for reasons other than money (e.g., storage space, own effort for operation, noise, size of the system, maintenance effort, later adaptability, ecological considerations, etc.).
And here the proposed gas condensing boiler in combination with solar thermal energy can certainly score points with simple supply, low area requirements, no additional storage space, and essentially no own effort for operation.

Best regards
Erik