ᐅ Heating System Choice: Air-to-Air or Air-to-Water Heat Pump

Hello everyone,
we are just at the very beginning of our home building journey – specifically in choosing the construction company. Neither of us are experts, and we are currently educating ourselves a lot -> please excuse us if some technical terms are unfamiliar or used incorrectly 😉
Among many other questions, we are uncertain about the heating system.

Construction Company A strongly recommends an air-to-air heat pump – meaning a central ventilation system with 'heating through the air flow.'
Company B suggests an air-to-water heat pump – combined with underfloor heating + still a central ventilation system.

And now about our lack of knowledge…
The air-to-air solution seems initially cheaper – but according to the advisor from Company B, there are disadvantages:
- Every room is the same temperature -> so having a cold bedroom and warm living room wouldn’t be possible?
- Warm air always rises -> so the floor would feel cold.

Neither of these issues would occur with underfloor heating since it can be controlled separately, and of course, your feet would be warm.
I don’t want to start a (new) fundamental debate – just wondering if you see it the same way? Unfortunately, we don’t know anyone who heats ‘with air’ 😉

Try searching for "thermal comfort with radiant and convective heat"

Where does the energy for the air-to-air heat pump come from? From the exhaust air or the outside air? In my experience, usually only an exhaust air heat pump is installed, which effectively provides very efficient ventilation. However, you will have to compensate for heat losses entirely with electricity.

Regarding floor temperature, you shouldn’t expect too much. Nowadays, the surface temperature is typically around 22°C (72°F). A really warm floor like in the 1980s would now feel like a sauna in the living room. You can also only expect limited differences between rooms. Exterior walls provide significantly better insulation than interior walls, so this balances out somewhat.

Still, I find you can feel the difference between heated and unheated rooms when walking in socks. It is possible to keep the bedroom 2–3 degrees cooler. But 25°C (77°F) in living areas and 17°C (63°F) in the bedroom is not achievable.

Basically, I would prefer a hydronic (water-based) system. This gives you full flexibility later on to replace the heat generator.

WilderSueden schrieb:

Where does the energy for the air-to-air heat pump come from?

There was mention of a crossflow heat exchanger – so if I understand correctly, from the exhaust air.

To summarize, with underfloor heating, small temperature differences are possible, but with air heating, the temperature is the same everywhere?
It was also mentioned that you could close the air vents if you don’t want to heat a room – but wouldn’t that worsen air quality (leading to mold growth), right?

KatlarOne schrieb:

I don’t want to start another fundamental debate — but do you all see it the same way? Unfortunately, we don’t know anyone who heats with air 😉 )

You can try searching for Proxon here in the forum (and also online).

Air-to-air (usually an exhaust air heat pump) is ideally suited for a house built between KfW 40 and Passive House standards. These buildings are so well insulated that their heating demand is extremely low. With a KfW 55 standard, you will most likely end up losing the initial savings during the first heating seasons due to the electric backup heating of the air-to-air heat pump.

Otherwise, as mentioned before, the heat is somewhat different. Rooms nowadays are generally evenly warm (although I consider a 2°C (3.6°F) difference as evenly warm).

Regarding the different rooms: With a warm air heating system, you can reduce heating or cooling only by restricting the airflow. At my grandmother's house, we had a warm air heating system powered by wood/coal. Back then, it was primarily a heating system, and the house ventilated itself automatically and without any control.

The bedroom is an air supply room; if you want to keep it cool in winter, you would have to reduce the airflow, which I find rather uncomfortable.

In general, with air-to-air systems, a clear separation between supply air rooms (bedroom, living room, children's room, etc.) and exhaust air rooms (bathroom, toilet, etc.) is not possible. I would find that very unpleasant.