Is air heating only sensible for heating loads below 10W/m²?

Companies like Schwörerhaus or Okal Haus offer air heating as standard. Now I found that this only makes sense at heating loads <10W/m².

If a house is classified as a 4l house, is that correct?
4l=40kWh/m²a -> 40,000/(24*365)= 4.6W/m²

Does the air always have to be heated by an air-water heat pump? That is not as efficient as other heat pumps.
Is the following calculation correct:

40kWh/m²*140m²=5600kWh / 2 (COP) * 0.20€/kWh = 560€ electricity costs/year?

Maybe the consumption and the COP are a bit higher, but roughly like this? If that is the case, why doesn't everyone do it? There probably isn’t a cheaper heating system in terms of construction (ventilation and heating in one). I probably overlooked something, right?

Hello,

Companies like Schwörerhaus or Okal Haus offer air heating as standard. Now I found that this only makes sense at heat loads <10W/m².

That is an average specific heat load. Individual room heat loads can definitely be higher! Moreover, this is the heat load according to the PHPP criterion. The actual heat loads according to DIN 12831 are generally higher.
As an explanation: The heat load is supposed to represent the extreme case. Therefore, in the calculation according to 12831, internal and e.g. solar gains are disregarded. Rightly so, because at -20°C at night there is no sun and the football team responsible for internal gains is currently on vacation! ;)
In the heat load according to PHPP, however, these gains are taken into account. :o

...If now a house is presented as a 4l house, that's correct, right?

Be very careful with the L/m² oil advertising! Quite a few have already got seriously burned there.

...4l=40kWh/m²a -> 40,000/(24*365)= 4.6W/m²

Well, it probably doesn't work that trivially; it would be nice if it were that simple. Then I could throw away all software and DIN regulations. So that is absolutely not correct!

...Does the air always have to be heated via an air-water heat pump?

The heat generator basically doesn't matter, only its capacity must match the building heat load. Otherwise, there will be serious problems. Either you freeze, have immense consumption costs, or the heat generator cycles itself to death.

...Is the following calculation correct:
40kWh/m²*140m²=5600kWh / 2 (COP) * 0.20€/kWh = 560€ electricity costs/year?

That is also completely wrong!

...I probably overlooked something, right?

Yes, of course, all the basics, you can't replace the complete MEP planning for a building with a couple of lines! :(
Be sure to watch out that nobody sells you nonsense!

Best regards

Mh, and what am I supposed to do with that now? I fully understand that a real heating bill is not that simple. But how is one supposed to estimate whether that is realistic? Can a house really be heated as advertised with low costs, or not? How does one verify the manufacturers' claims?

And what do you mean by the 4l/m², which people have burned their fingers on.

...I am fully aware that a real heating bill is not that simple. But how is one supposed to estimate whether it is realistic?

A layperson cannot manage that. External professional support is needed here.

...Can such a house really be heated as advertised with low costs, or not?

That is exactly the crucial point. Theoretically, on paper that has been nicely calculated "can" - but unfortunately, that is often not the case! Afterwards, improvements are hardly possible.

...How do you check the manufacturers' specifications?

By having the building verified through an external HVAC planner. Or you have the provider create a real consumption forecast before signing a contract and, after prior review, make this part of the contract.

...And what do you mean by the 4l/m² that caused people to get burned?

There are various providers who advertise using these l oil/m² equivalents. Unfortunately, in many cases the actual consumption is significantly higher. When this is taken into account, the prices of these properties are naturally much too high.

Best regards.