Heating replacement in old buildings - gas or air heat pump

Dear forum members,

We recently bought a house and have been in contact with our heating engineer for some time now, considering how to renovate the heating system. The house is an end-of-terrace house built in a split-level design – the floors are therefore largely open. Currently, a fairly new, 4-year-old gas condensing boiler is installed. The problem is that all radiators are connected to a single-pipe system, which is very inefficient (and also not compatible with later new heating systems). This was the reason we started thinking about the heating system at all. Otherwise, we would have just replaced a few radiators. After many discussions and considerations, we are now at least at the point where we would like to switch to underfloor heating (the rooms are quite small and the radiators significantly disrupt the room layout, and we have a small child who usually spends half the day on the floor). Since the house needs to be completely renovated (floors, walls, bathrooms), we are going to tear everything out anyway. Installing the underfloor heating is therefore not a significant additional effort.

Our heating engineer’s suggestion was an underfloor heating system combined with an air-source heat pump, as there are currently good subsidy conditions for this. We initially thought the idea was great, but we are now having doubts. Our house is exactly 3 meters from the property boundary, and the air-water heat pump would have to be installed within these 3 meters. However, we definitely do not want any trouble with the neighbors and are not even sure ourselves whether we will eventually be very annoyed by the humming of the air-water heat pump, since our kitchen window/dining room would be diagonally above the installation site of the pump.

So we have now been considering whether it is even necessary to get rid of the new condensing boiler. Can we not also operate the underfloor heating with this system? Of course, the subsidy would then be lost, but somehow this seems more sensible to us right now. Or are we wrong and the gas costs will explode when operating underfloor heating?

The second point that bothers us is the quite high electricity costs of the air-water heat pump. According to our calculations, the electricity costs would be about as high as the gas consumption with the currently installed gas heating system (the house is still rented out, so we know the consumption). Apart from ecological considerations, we see no advantage for us.

We would be very happy to receive feedback, as we gradually need to make a decision.

Definitely keep the gas heating as long as the subsidy does not cover 100% of the costs of the air-water heat pump. Moreover, it is not about a possible demand, but primarily about the flow temperature. Only with the lowest possible flow temperature can an air-water heat pump be operated efficiently. What insulation measures are you planning?

You have to calculate this exactly and determine the heat demand after insulation precisely.

There are both KfW programs for renovation and Bafa funding.

Since all measures for underfloor heating can also be funded in old buildings, it can definitely be worthwhile to replace the BWT.

Insulation of the house is not planned, as it is architecturally difficult to implement this consistently. However, we will replace the windows and insulate the attic and the basement ceiling.

This must be calculated precisely, and the heat demand after insulation must be determined exactly. There are both KfW programs for renovation and Bafa funding. Since all measures for underfloor heating can also be subsidized in old buildings, it can definitely be worthwhile to replace the BWT.

We have estimated this based on an offer from our heating installer. Since there apparently is also funding for the new installation of floors, we would be about even with both options. For us, as mentioned, the noise factor remains. Or have the new devices become significantly quieter by now?

Noise factor

???? What noise? From the heat pump? That's a rumor. Isolated cases yes – just as there are isolated cases where indoor units make noise (a gas heater also makes noises).