New single-family house construction | Selection of the "right" heating technology

Good morning!

Clearly: there is no perfect heating system. But which one could be the right choice for us?

In connection with the construction of a new single-family house with 170m² of living space, 1.5 stories, the architect was initially given the requirement that it should meet KfW55 standard. Also, to take advantage of the subsidies. At the same time, we found the ground-source heat pump very appealing – although expensive. Furthermore, a controlled residential ventilation system was set, and the photovoltaic system should at least be prepared.

After delving deeper into the subject, it is now clear that it will not be a KfW55 standard. We "fail" just barely on the value of the average transmission heat loss.

With 8cm more insulation in the exterior wall, we would achieve this, but that would come at the expense of living space, since the building envelope is almost fully used. According to our architect (simultaneously also an energy consultant), the additional costs would be about €2000, while the savings on heating costs would be about €30/year.

Moreover, KfW55, after closer planning, also makes no sense for us in terms of financing.

Nevertheless, we initially continued with the plan to install a ground-source heat pump. An air-water heat pump has always been – gut feeling – unappealing to us, and the solar thermal system on the roof bothered us somehow with the gas condensing boiler, since it is required for KfW55 for the renewable portion.

Meanwhile, the thermal protection certificate of the building is available, and the heating load (~7.5KW) is also known. In addition, we have received the first quotes for a ground-water heat pump and an air-water heat pump. Now, at the latest, we are starting to rethink!

Let me briefly compare:

Ground-water heat pump: ~ €18,000 (incl. multifunctional storage)

+ Deep drilling: ~ €10,000

- Subsidies BAFA and NRW Progress: ~ €6,000

Total: ~ €22,000

Air-water heat pump: ~ €16,500 (incl. multifunctional storage)

I do not have an offer for a gas condensing boiler including the appropriate storage. Roughly, one seems to come to about €10,000 (including storage and installation). Added to that, the costs for the chimney and gas connection, we at most are on par with the air-water heat pump.

Since we now do not want to meet the KfW55 standard but only build according to the Energy Saving Ordinance, we do not need solar thermal. However, the building envelope roughly corresponds to KfW55 standard – so it is very tight.

Regardless of the idealistic value and ecological aspects, the additional costs for the ground-water heat pump somehow no longer make sense! That then brings the gas condensing boiler back into play, especially since the heating load is very low due to the building envelope anyway.

We are really torn back and forth and would appreciate some feedback on our view.

Best regards,
zehn0813

The gas boiler will be around 10 including solar for water heating, with a branded device. What would be added are the costs of the gas connection. Here with us around 1500,- Euro. The air-to-water heat pump does not pay off its extra cost, I am sure of that. Economically, it would be a gas boiler. Karsten

If the gas connection cannot be installed with increased effort... then yes, definitely the cheapest option...

Why should the pure heat pump as a brine variant be more expensive than an air-water heat pump? 10T€ for the drilling is also a lot, is there a concrete offer or a price indication? How deep? 6000€ funding with progress nrw suggests 100m depth, but that is rather little for 7.5kw, at the same time the drilling with 10T€ would be clearly too expensive for that. Our architect also estimated costs that were way too high for that (because that’s the luxury variant, so it has to be expensive and is provided with a buffer). If you care about the brine-water heat pump with probe, just call two drilling companies. Price indication with heat load takes 5 minutes on the phone.

Why do you have to increase insulation by 8cm when you just barely miss KFW55? 8cm more is already significant. In the case of EPS, "just barely missing" can be enough to switch to WLG032 (Neopor). Completely without thicker insulation. But KFW isn’t really worth it anyway. Extra effort due to the surveyor and the loan conditions have become more expensive again a few days ago and at least for us are finally done with.

To be honest, the heating load seems pretty high to me. 7.5kW for 170m² would be ~45W/m². We are at 35...

Is there a basement or attic included that is not counted in the living area? What wall/roof construction do you have?

It could also be that the controlled ventilation was not taken into account and thus the ventilation heat loss is driving the heat demand so high.

I would like to see the heating load calculation...

The gas boiler including solar for water heating will be around 10,000, using a brand-name device. What would be added are the costs of the gas connection. Here with us about 1,500 euros. The air-water heat pump does not pay off its premium, I am sure of that. Economically, the gas boiler would be better. Karsten

With us 2,500.00€. Then my assumption that the costs with the air-water heat pump are comparable or even lower is not so bad. Especially since ST is already included in the costs. I had misinformation regarding the assumption that the ST would not be needed.

If the gas connection can be made without increased effort... then yes, definitely the cheapest option...

No increased effort. The connection via the multi-utility entry is supposed to cost 2,500.00€.

Why should the pure heat pump as a brine variant be more expensive than an air-water heat pump? 10,000€ for the drilling is quite a lot, is there a concrete offer or a price indication? How deep? 6,000€ funding with Progress NRW suggests 100m depth, but that is rather little for 7.5 kW, at the same time the drilling at 10,000€ is far too expensive for that. Our architect also estimated much too high costs for this (because it is the premium variant, it must be expensive and is buffered). If you care about the brine-water heat pump with probe, just call two drilling companies. Price indication with heat load takes 5 minutes on the phone.

I have a concrete offer for a deep drilling. 160m (2x80m) – deeper than 100m brings other consequences. Progress is 10€ funding per meter drilled. Additionally, 4,500.00€ funding from BAFA.

Why do you have to strengthen the insulation by 8cm when you just miss KFW55? 8cm more is already substantial. When "just missed", with EPS it might be enough to switch to WLG032 (Neopor). Completely without thicker insulation. But KFW is not really worth it anyway. Extra effort due to surveyor and loan conditions have become more expensive again just a few days ago and for us are finally off the table.

We build the classic wall structure from KS stone, mineral wool insulation, air layer, and facing brickwork. This results in 47cm with 16cm external wall insulation.

"Just missed" means that we undershoot the value of the average transmission heat loss by only 21.6%, but it would have to be 30% to meet the KfW55 standard.

To be honest, the heating load seems quite high to me. 7.5 kW at 170m² would be ~45 W/m². We are at 35... Is there still a basement or attic included that is not part of the living area? What wall/roof construction do you have? It could also be that the controlled residential ventilation has not been taken into account and thus the ventilation heat loss raises the heating demand so high.

The primary energy demand according to WSNW is 19 kWh/(m²a). The base area is just under 230m². Living area 170m². 1.5-story with an expanded attic.

I would ask to see the heating load calculation...

There is no heating load calculation yet. The 7.5 kW is a rough estimate by the company to create an offer. The exact calculation is to be made after contract award.

I am neither enthusiastic nor satisfied about that. It feels like "buying a pig in a poke."