Indoor installation of heat pump: What should be considered regarding the air ducts?

Hello everyone,

I am dealing with the necessary replacement of our old oil heating system on the ground floor (125 sqm heated, house without a basement). Before talking to installers, I first need to inform myself about some topics. We are considering installing an air-to-water heat pump, preferably for indoor installation. I have a few questions for the experts among you and would appreciate your advice:

An outdoor installation of an air-to-water heat pump (air heat pump) will only be possible in one location due to the special property situation (distances, boundary layout, underground lines). This would result in about 10 m of piping to the actual boiler room with all the pipes, distributors, etc.

1. Would this basically be a disadvantage or a bigger problem regarding efficiency, installation costs, lifespan?

Therefore, an indoor installation of the air heat pump seems to be an option for us. The previous oil room is right next to the boiler room and can certainly bear the weight of an air heat pump without problems, so installation there and breakthrough here of an air duct for fresh air on the outer wall. However, the necessary air ducts must share one outer wall (no house corner available). The exhaust air duct would have to be located in the adjacent boiler room due to the narrow width of the oil room (breakthrough of the inner wall).

2. What distance between the air ducts is required to reliably prevent a thermal short circuit?

3. Can the exhaust air duct be positioned lower than the fresh air duct of the air heat pump (due to many installed pipes in the boiler room on the relevant wall)?

4. Are the air ducts of common air heat pump providers for indoor installation flexible regarding the exhaust air duct routing (number of bends and height of the outer wall breakthrough) or are there restrictions (same height of fresh air and exhaust air ducts)?

5. What should be considered to avoid vibrations and noise in indoor installation?

6. Is an additional window for fresh air needed in this room, or is a ventilation grille sufficient?

7. We would drain condensate water through a pipe via a breakthrough in the outer wall into the soil 1 m deeper. What maximum amount of condensate water can be expected per day at full load? Is that a lot of water?

8. How large are the usual air duct openings in the outer wall generally (range)?

Many thanks for your assistance.

I am not an expert and can only report from my experience. We had a monoblock combined unit (air-water heat pump + controlled residential ventilation) in our last house, and I am currently building with a split heat pump.

1. I checked and our split unit allows refrigerant pipe lengths from 3 to 30m. I will assume here that a bit of digging is necessary.
2. We had a similar problem. A corner of the house was available, but my wife rejected it for aesthetic reasons. Ultimately, our general contractor (at their cost) routed the supply air through the carport to solve this problem.
3. I think so, that was the case for us. Supply air above the carport, exhaust air at foot level. You could actually put a box of beer in front to cool it down.

5. Because it was a new build, we had a steel foundation for the heat pump. This is supposed to avoid vibrations. We could still hear it, but not much, and it got lost in the daily noises. A door with better soundproofing would maybe be nice, but when the utility room and living room doors were closed, we hardly or did not hear it.

7. Apart from the defrost process, there was not much to reckon with. Both of ours are made with some kind of funnel construction; we saw that you have to be a bit careful with dust as it blocks the drainage.

8. Ours was about 30x30, which also had controlled residential ventilation integrated.