ᐅ Air-to-Air vs. Air-to-Water Heat Pump for a KfW55 House – Importance of Cooling Function

Hello everyone,
we are currently deciding between several prefab house suppliers, and a major difference is the heating system offered. Some suppliers install an air-to-air heat pump as standard (cooling available at extra cost), while others provide an air-to-water heat pump with underfloor heating and a ventilation system with heat recovery (an air conditioning unit can be added). Geothermal or groundwater as a heat source will likely not be an option for the plot we are currently considering. It will be a KFW 55 house, initially without photovoltaics for cost reasons, but solar panels are planned to be added later.

We have already read quite a bit on the topic, but as laypeople, we find it difficult to make a decision regarding the heating system. It is important to know that we are very sensitive to heat and want to include active cooling right from the start. In the worst case, we would need to heat/cool only individual rooms.

These are the advantages and disadvantages we know so far:

Heat Pump	Advantages	Disadvantages
Air-to-Air with Cooling Function	Heating and cooling in one system Relatively inexpensive upfront	Noise level still needs to be checked (is it different from a ventilation system noise?) More difficult to control temperatures individually in different rooms compared to underfloor heating
Air-to-Water with Underfloor Heating + Air Conditioning	Switching to other heat sources is easier Air conditioning works very well together with photovoltaics (you want to cool mainly when there is a lot of sunshine) Warm floors in winter	More expensive upfront, especially including the air conditioning (exact cost difference is not clear yet) Air conditioning without photovoltaics means high energy costs
Air-to-Water with Underfloor Heating with Cooling Function	Switching to other heat sources is easier	Only a few degrees of cooling possible Cold floors in summer (a very important disadvantage for health reasons)

In principle, this results in 3 options that we are currently considering (we were advised against underfloor heating with cooling function for the reasons mentioned):

• Install air-to-air heat pump with cooling function
• Install air-to-water with underfloor heating, add air conditioning when photovoltaics are installed, and live with the heat until then
• Install air-to-water with underfloor heating and air conditioning, tolerate high cooling costs until photovoltaics are added

Which option would you prefer, or do you see another solution? Do you have any ideas which option would be better in terms of running costs? Because we probably have a rather expensive plot and need to watch costs during construction, air-to-air currently sounds like the better solution to us.

We would appreciate your assessments.

Assessment: In the end, there are exactly two reasonable solutions left: air-to-water heat pump plus air conditioning, or air conditioning only.

Why? An air-to-air heat pump makes no sense in a KfW 55 house. Although it reduces initial investment costs (a nice selling point), an air-to-air heat pump should be installed in houses built to KfW 40 or passive house standards for consumption reasons. Therefore, no further argument is needed regarding the (ineffective) cooling option.
You wouldn’t be happy if a) the cooling performance is poor and b) you save a five-figure amount initially but end up paying double or even higher heating costs on an ongoing basis. Not to mention the entirely different heating technology with its different heat quality, which for me is a deal-breaker.

If I had to decide: split air conditioning for heating and cooling. Affordable, effective, and reasonable in ongoing maintenance costs.

P.S. Costs are not only monetary. Reduced quality of life is also a cost you need to consider. Besides, it makes no sense to wait to install air conditioning. The costs you will face later are significantly higher than installing it immediately. You don’t have to run it if saving a few euros per year is important to you (although I don’t consider operating an air conditioner for a few weeks a year with electricity costs of about €25 (~$27) per month to be too expensive).

What health reasons speak against a radiant floor cooling system?

From my perspective, an air-to-air system can also be described as follows.

You have a heat pump that generates heat, warms the air, and distributes it into the room through ventilation outlets—similar to how a car works.

If the heat output is not sufficient due to cold outdoor temperatures, each outlet has an additional small electric heater (a "hairdryer") that provides the extra necessary warmth.

Whether you find this acceptable and worth the savings is up to you. This also explains why it is cheaper.

However, this is just an exaggerated, non-expert opinion from casual conversation.
Oh, and try googling Proxon.

RotorMotor schrieb:

What health concerns are there regarding underfloor cooling?

I believe expectations for the cooling are often much higher than what it can actually deliver. In the office, I often walk barefoot (IT people are allowed to do that!), and on the carpeted floor it feels cool but not cold. Uncooled tiles feel worse.

If you are sensitive to heat, I would definitely put some thought into shading. Don’t forget about the light when planning shading— with proper design, you can shade the sunny sides while still letting light in on the others.

I’ve already mentioned this in a few other threads, but briefly: I use cooling through the regular underfloor heating system, which is controlled by the photovoltaic system. It works perfectly, and NO, nobody has complained about cold feet. The heat simply disappears. The reason it’s sufficient for me is a) the very well-insulated house and b) the location at 550m (1,800 feet) in the foothills of the Alps – it probably wouldn’t be enough in Cologne on the Rhine. A conventional air conditioning system obviously has a lot more power and also dehumidifies.

Never building a house again without some form of cooling. At this location, I would gladly rely on underfloor heating cooling again, but in hotter or more humid areas, I would opt for a proper air conditioning system right away. Control is easily possible nowadays via Home Assistant, so it can be set to only turn on when the photovoltaic system is generating power – without the usual time delay associated with underfloor heating.