Timber frame construction and gas condensing boiler or air-to-water heat pump?

Hello everyone,

we are still deep into the house planning, and currently I am personally somewhat desperate about the heating solution (2 people, later about 2 children desired).

We have two offers, one from a local solid house builder and one from a local timber frame house builder.

The solution with the solid house would currently be:
- 172m²
- air-water heat pump Stiebel Eltron WPL 13 ACS (or cost-neutral gas condensing boiler with solar from Vaillant)
- central ventilation system from Wolf

The timber frame company has now surprised us with a very interesting floor plan. The equipment here would be:
- 168m²
- Junkers Cerapur ECO ZSB 14-5.2 C21 and a 120-liter hot water tank
- decentralized ventilation prepared (connections and everything available) but not yet installed, as according to the company we do not need it.

What now surprises me is why we suddenly do not need solar thermal anymore (I thought because of the Energy Saving Ordinance 2016).
The company also told us that they would not recommend an air-water heat pump because, for example, there is still the problem with legionella and that the costs would drive up a bit. Allegedly the insulation in a timber frame house is very good after all.

I would now be interested in how the costs would look like for gas condensing boiler and air-water heat pump. We would build in the area with postal code 268xx, so quite mild (except for last winter).

Maybe someone here can untangle the knots in my head.

Edit: Of course I have already tried to read quite a lot, but currently I am somewhat overwhelmed.

According to the currently ongoing discussion, gas sellers will probably have to purchase CO2 certificates and factor these into their prices, which now speaks in favor of air-water heat pumps, unless they exploit this and also raise the price with a "Greta likes it" label on it.

According to the current discussion, gas sellers will probably have to purchase CO2 certificates and factor these into their prices, which now speaks in favor of air-to-water heat pumps, unless they take advantage of this and also raise the price with a Greta likes it label on it.

Mh, yip. That's kind of my concern too, that right now we don't really know exactly what is coming at us in terms of gas.

I would now be interested in how the costs would look for gas condensing boilers and air-to-water heat pumps. We would be building in the postcode area 268xx, so quite mild (except for last winter).

If the air-to-water heat pump is properly planned (no buffer, underfloor heating well designed with a maximum supply temperature of 30°C) and operated (hydraulic balancing, settings, no ERR), the running costs are about €200-€300 per year lower than gas at current prices. Consumption costs are similarly high, but with the heat pump you have no basic fee (do not use a second electricity meter) and no/less maintenance and no chimney costs. The planning of the heat pump is often botched, so read up yourself using a search engine. Whether it is worth it compared to gas also depends on the (additional) price you have to pay for the heat pump and, of course, the future costs for electricity/gas. Regarding legionella, there are these options: - Fresh water station (expensive) - Keep hot water temperature always >50°C, which reduces the efficiency of the heat pump - Regularly “disinfect” hot water using an immersion heater, which costs electricity - Dimension hot water storage appropriately so the water doesn’t stand long, i.e., keep it as small as possible (200-300l) Most people do the latter, including us: 200l for up to 4 people, rarely bathe. However, I wouldn’t do that for rental properties. Solar thermal can be dispensed with when using a ventilation system, but few general contractors can calculate that. Without it, it gets difficult, so investigate further why it is supposedly possible – so that you don’t end up with collectors mounted on the roof after all.

If the air-water heat pump is planned properly (no buffer, underfloor heating well designed and planned for a max supply temperature of 30°) and operated (hydraulic balancing, settings, no ERR), the running costs are about €200-300 p.a. lower than those of gas at current prices. Consumption costs are similarly high but with the heat pump you have no basic fee (do not take a second electricity meter) and no/less maintenance and no chimney costs. The planning of the heat pump is often botched, i.e. you need to research it yourself via search engine. Whether it is worth it compared to gas depends particularly on the (additional) price you have to pay for the heat pump and of course the future costs for electricity/gas.

Regarding legionella, these are the possibilities: - Fresh water station (expensive) - Hot water temperature always >50°, which reduces the efficiency of the heat pump - Regularly "disinfect" hot water via electric heating rod, which costs electricity - Dimension the hot water tank appropriately so that the water does not stand for a long time, i.e. as small as possible (200-300l)

Most probably do the latter, as do we: 200l for up to 4 people, rarely bathe. However, I would not do this when renting out.

Solar thermal can be dispensed with if there is a ventilation system, but very few general contractors can calculate that. Without it is difficult, so investigate further why it is supposedly possible – so that you don’t end up with collectors mounted on the roof after all.

Called the company again today. Apparently, the Energy Saving Ordinance is exceeded, or there is a paragraph that makes it possible. Therefore, no solar collector has to be installed.

Only with gas? Sounds exciting. I have doubts. Or is the uninstalled ventilation included?