Right heating for KFW70 new building?

First of all Hi @ all

We want to treat ourselves to a new building, planned is a Kfw70 house from Massa Haus with 160m² living space.

But I am still totally undecided about which heating system to choose

There are no guest lines, so I am dependent on renting a tank.

A gas boiler with a 300L storage tank and about 5m² flat-plate collectors is included as standard

A controlled ventilation with heat recovery is always included

We have first decided on an air heat pump with underfloor heating. (about 13k) Since it is a compact system, the storage will probably be somewhat smaller, but for an additional 1500€ we would also have 2 high-performance tube collectors on the roof. (about 14.5k extra compared to the standard)

If we now calculate differently and stick with the gas boiler, but still have underfloor heating with a 750-liter storage tank (160Trin and 590 buffer) with hot water and heating support with about 10m² (about 16.5k extra)

An advantage I have already read about is that with the heat pump I have much lower maintenance costs (inspections, chimney, etc...)

I am really unsure now which to decide on

If heat pump then have the hot water collectors installed and rather save the money or better yet spend more and have solar electricity collectors installed on the roof? (if you can even get anything for about 3.5k)

Hello, a lot has already been written about this. Just use the search function.

....Standardmäßig dabei ist eine Gastherme mit 300L Speicher und ca 5m² Flächenkollegtoren.

Liquid gas has significant problems with modulation (minimum output). Solar thermal systems usually do not pay off in single-family homes.

.... Da es eine Kompaktanlage ist,...

Compact systems are usually the worst choice.
Without adequate calculation (including heating load, consumption forecast) it is hardly possible to give a reliable recommendation. => guessing game!

Best regards

That is a good question regarding the heating load.

But if you say that the gas system is not so great and neither is the compact system, what should I then take? It should also not exceed my budget.

But preferring the gas boiler currently is the right way to think, isn't it?

Hmm, I thought that would be something useful, especially because of the heating support

That is a good question regarding the heating load.

For necessary calculations, this might help:

https://www.hausbau-forum.de/threads/Erdwärmepumpe-wartung-wie-was-zu-beachten.4914/

...But if you say that gas is not so great and neither is the compact unit, what should I choose then?

An alternative would be, for example, a fully modulating inverter split system (air heat pump) with suitable capacity (performance curve).

...But that I currently prefer the gas boiler, that's the right reasoning, isn't it?

Not at all, because of the solar thermal system. Gas is rather suitable in connection with the 15% rule (better insulation) and without a solar thermal system. With liquid gas, a few special considerations have to be taken into account due to the too high minimum capacity in order to avoid frequent short cycling.

...Hmm, I thought that was something reasonable, especially because of the heating support

The seller surely thinks so too. Unfortunately, a completely different picture emerges when looking at the actual balances.

best regards

okay that sounds plausible, but honestly I haven't understood the thing with the gas yet.

I have to ask tomorrow if I can paint the heating from the house package.

Because like that I only have about 16k left for something else, and I certainly won't get anything for that, right?

Hello Dunda,

the heating energy demand in a Kfw 70 house is very low, so only small system capacities are required. Due to the low demand, the saving potential is also low, and the significance of the energy source decreases. For this reason, investment costs play a greater role, as high investments must also bring high cost savings. The advantage of gas condensing technology is that these costs are very low or, as in your case, the system is already included. If you want to do something now and really reduce the consumption of fossil and nuclear-based energies, then the sun remains as an inexhaustible source. With a solar thermal system that takes over the hot water preparation and supports the heating, there is the possibility to make an environmental contribution and to decouple somewhat from energy price developments.