New building KfW55 with gas, solar, and controlled residential ventilation with heat recovery

we will also build soon and achieve KfW55, we prefer gas for heating. The general contractor told us that KfW55 with gas is possible (ST+ventilation).

But certainly a drawn-out "possible"?

However, it may be that instead of the monolithic construction (36.5 cm aerated concrete) we have to take a 20 cm block plus thermal insulation. We can live with that as well...

Not just 24 + 16. Under the BP additional insulation is required; if you stick with gas as the heat generator, it is very likely that the amount of insulation in the attic must also be increased.

Soon an energy consultant will deal with it and say how to realize it.

I hope you keep us updated.

Rhineland regards

We are currently facing the same problem. We were offered an air-to-water heat pump, a decentralized ventilation system without heat recovery, and 36.5 aerated concrete. However, we would prefer to build with gas (air-to-water heat pump too inefficient (estimated annual performance factor 3 by the energy consultant) and thus higher monthly heating costs), ST, and a central ventilation system including heat recovery (if the budget allows --> refers to the ventilation system). It should not be a KFW house. Is the option with gas, etc., without additional styrofoam insulation, which we would like to avoid, possible? A third option (brine-to-water heat pump with collectors, controlled residential ventilation with heat recovery, 36.5 aerated concrete) also plays a role. However, I assume that the investment costs will be highest here, right? What should one expect on average, and how does the annual performance factor look in this case? Furthermore, I would also be interested to know whether the investment in a decentralized ventilation system without heat recovery is worthwhile at all? Thanks for your opinion and assessment.

Hello!

A quick update from us:

The energy consultant has done the calculations and we will now build with gas + controlled residential ventilation with heat recovery. Additionally, extra insulation will be added to the floor slab and roof. However, this is still cheaper than the PV system, which we wanted to do without and now will. Our house is very compact and the windows are well oriented. This is how the calculation worked out.

Best regards,

XeNiA

Hello!

A brief update from us:

The energy consultant did the calculations and we will now build with gas + controlled residential ventilation with heat recovery. In addition, there will be extra insulation for the base slab and roof. However, this is still cheaper than the solar thermal system, which we wanted to forgo and now will.
Our house is very compact and the windows are well oriented. So this calculation worked out.

Best regards,

XeNiA

Hi XeNiA,

Are the costs the only reason why you want to forgo the solar thermal system? We place great value on the solar thermal system because it reduces gas costs to a minimum during the non-heating period since the warm water for the shower and so on comes from the solar thermal system...

Regards

I currently live in a house built in the mid-70s with a very new gas condensing boiler. I record consumption at least monthly. With four people, we used about 350 kWh of gas per month in summer – that is, without heating operation and only hot water. That corresponds to consumption costs of about €21. By comparison, in November during heating operation, we used about 3300 kWh, so not quite ten times as much.
Insight? Hot water with a gas heater is a negligible byproduct of heating operation.

How expensive is the PV system again?

It will never pay off. PV is done to achieve the renewable quota according to the Energy Saving Ordinance. As little as possible.
I think it’s great that XeNiA manages to reach KFW 55 purely with controlled residential ventilation/heat recovery. Presumably, the investment is higher than installing PV, but at least it has real value in the form of increased comfort through air quality and mold prevention. PV is dead capital.

Yes, we have done a lot of back and forth calculations and in the end, it always comes out as the most cost-effective option (in our case).

This topic has been the most discussed so far and everyone recommends something different.
Whether we are making the right decision can probably only be seen in a few years after several heating seasons.

The controlled residential ventilation was important to us and since it already costs 12000€, we had to save money elsewhere

Regards