ᐅ Timber Frame Construction with a Gas Condensing Boiler or an Air-to-Water Heat Pump?

Hello everyone,

we are still deep in the house planning phase, and at the moment, I am personally struggling a bit with the heating solution (2 people, with about 2 children planned later).

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

The solution for the solid construction would currently be:
- 172m² (1850 sq ft)
- Air-to-water heat pump Stiebel Eltron WPL 13 ACS (or at no additional cost a gas condensing boiler with solar by Vaillant)
- Central ventilation system by Wolf

The timber frame company surprised us with a very interesting floor plan. The features here would be:
- 168m² (1810 sq ft)
- Junkers Cerapur ECO ZSB 14-5.2 C21 and a 120-liter (32-gallon) hot water storage tank
- Decentralized ventilation prepared (connections and everything included) but not yet installed, as the company said we wouldn’t need it.

What really surprises me here is why solar thermal is suddenly no longer required (I thought this was mandatory due to the 2016 Energy Saving Ordinance).

Also, the company told us they would not recommend an air-to-water heat pump, because, for example, there would still be issues with legionella, and the costs would increase somewhat. Allegedly, the insulation in a timber frame house is very good anyway.

I would be interested to know how the costs compare between a gas condensing boiler and an air-to-water heat pump. We would be building in the postal code area 268xx, so quite a mild climate (except for last winter).

Maybe someone here can help untangle my thoughts.

Edit: Of course, I’ve already tried to read quite a bit, but at the moment I am a bit overwhelmed.

According to the ongoing discussion, gas suppliers will likely have to purchase CO2 certificates and incorporate these costs into their prices, which currently favors air-to-water heat pumps—unless they take advantage of this situation and also raise prices using a "Greta likes it" label.

Nordlys schrieb:

Based on the current discussion, gas suppliers will likely have to purchase CO2 certificates and include these costs in their prices, which currently favors air-to-water heat pumps—unless they take advantage of this and raise prices anyway with a "Greta likes it" label on them.

Hmm, yeah. That’s kind of my concern too—that right now it’s unclear what exactly we can expect regarding gas prices and regulations.

SlippySken schrieb:

I am interested in the cost comparison between a gas condensing boiler and an air-to-water heat pump. We plan to build in the postal code area 268xx, which is relatively mild (except for last winter).

If the air-to-water heat pump is properly designed (no buffer tank, underfloor heating well planned with a maximum supply temperature of 30°C (86°F)) and operated correctly (hydraulic balancing, proper settings, no heat emitter resistance), the running costs are about €200-300 (approx. $220-330) per year lower than those of gas at current prices. Consumption costs are similar, but with the heat pump you have no fixed charges (no need for a second electricity meter) and lower or no maintenance and chimney costs. The design of heat pump systems is often done poorly, so it’s worth researching thoroughly yourself using search engines. Whether it is worthwhile compared to gas also depends significantly on the purchase price of the heat pump and, of course, future prices for electricity and gas.

Regarding legionella prevention, the following options exist:
- Fresh water station (expensive)
- Keeping the hot water temperature always above 50°C (122°F), which reduces the heat pump’s efficiency
- Regularly disinfecting the hot water using an electric heating element, which consumes electricity
- Properly sizing the hot water storage tank to avoid water standing for too long, so keeping it as small as possible (200–300 liters (50–80 gallons))

Most people do the latter, including us: 200 liters for up to 4 people who rarely bathe. However, I would not recommend this if the property is for rental.

With a ventilation system, solar thermal can be omitted, but few general contractors seem to include this in their calculations. Without solar thermal, it becomes difficult, so look into why this is supposedly possible—not to end up with collectors installed on your roof after all.

boxandroof schrieb:

If the air-to-water heat pump is properly designed (no buffer tank, underfloor heating well designed and planned with a max flow temperature of 30°C (86°F)) and operated (hydraulic balancing, correct settings, no electrical resistance heater), the annual running costs are approximately €200-300 less than those of gas at current prices. Consumption costs are similar, but with the heat pump you avoid a basic fee (do not install a second electricity meter) and have no or lower maintenance costs as well as no chimney expenses. The planning of heat pumps is often botched, so it is worth researching on your own using search engines. Whether it is economical compared to gas mainly depends on the extra cost you pay for the heat pump and, of course, future prices for electricity and gas.

Regarding legionella prevention, there are these options:
- Fresh water station (expensive)
- Keep hot water temperature always above 50°C (122°F), which reduces the heat pump’s efficiency
- Regularly "disinfect" the hot water using an electric heating element, which consumes additional electricity
- Properly size the hot water storage tank to avoid water stagnation, i.e., keep it as small as possible (200-300 liters (53-79 gallons))

Most people choose the latter approach, including us: 200 liters (53 gallons) for up to 4 persons, with infrequent bathing. However, I would not recommend this for rental properties.

Solar thermal systems can be omitted if there is a ventilation system, but few general contractors can calculate this properly. Without solar thermal, it will be difficult, so investigate further why it is supposedly possible — so you don’t end up having solar collectors installed on your roof after all.

I spoke with the company again today. Apparently, the energy saving ordinance is exceeded or there is a paragraph allowing it in that case. Therefore, no solar collector needs to be installed.

Only with gas? Sounds interesting. I have some doubts. Or is the uninstalled ventilation system being included?