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

Companies like Schwörerhaus or Okal Haus typically offer air heating as a standard option. I found that this is really only efficient when the heating demand is below 10W/m².

If a house is classified as a 4-liter house, that should be correct, right?
4 liters = 40kWh/m²/year -> 40,000 / (24 * 365) = 4.6W/m²

Does the air always have to be heated by an air-to-water heat pump? That type of heat pump 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 per year?

Maybe the consumption and COP are somewhat higher, but roughly like this? If that is the case, why doesn’t everyone use this? A cheaper heating system in terms of installation (ventilation and heating combined) probably does not exist. I guess I must be missing something, right?

Hello,

Arno schrieb:
Companies like Schwörerhaus or Okal Haus typically offer air heating systems as standard. I found that these are only sensible with heat loads <10W/m² (3.2 BTU/h·ft²).

That corresponds to a moderate specific heat load. Individual room heat loads can definitely be higher! Also, this is the heat load according to the PHPP (Passive House Planning Package) standard. The actual heat loads according to DIN 12831 are usually higher.
Explanation: The heat load is meant to represent an extreme scenario. Therefore, internal and, for example, solar gains are not considered in the calculation according to DIN 12831. This is justified because at -20°C (−4°F) at night, there is no sunshine and the “football team” of internal gains is on vacation! 😉
However, in the PHPP heat load calculation, these gains are included. :o

Arno schrieb:
...If a house is described as a 4-liter house, that’s correct, right?

Be very careful with the L/m² oil consumption advertising! Many have already seriously gotten burned by that.

Arno schrieb:
...4l = 40 kWh/m²·a -> 40,000 / (24*365) = 4.6W/m²

Well, it’s not that simple, and it would be great if it were. Then I could discard all software and building standards. This is absolutely incorrect!

Arno schrieb:
...Does the air always have to be heated through an air-to-water heat pump?

The heat generator generally does not matter, as long as its capacity matches the building’s heat load. Otherwise, you will face serious problems. You will either be cold, incur huge energy costs, or the heat generator will short-cycle itself to death.

Arno schrieb:
...Is the following calculation correct:
40 kWh/m² * 140 m² = 5600 kWh / 2 (efficiency factor) * 0.20 €/kWh = 560 € electricity cost per year?

This is also completely wrong!

Arno schrieb:
...I probably missed something, right?

Yes, of course, all the fundamentals. You cannot replace a comprehensive building services engineering plan for a building with a two-line calculation! 🙁
Make sure nobody sells you nonsense!

Best regards

Hmm, so what am I supposed to do with this now?
I fully understand that a real heating bill isn’t that simple. But how can you estimate if this is realistic?
Is it really possible to heat a house as advertised with such low costs, or not? How do you verify the manufacturers’ claims?

And what do you mean by the 4 liters per square meter, which has caused people to get burned?

Arno schrieb:
...I fully understand that a real heating bill is not that simple. But how can you estimate whether it is realistic?

A layperson cannot do this. You need external professional support here.

Arno schrieb:
...Can a house really be heated as cheaply as advertised, or not?

That is exactly the crucial point. Theoretically, on paper with ideal calculations, it "can" – but unfortunately, this is often not the case! Retrofitting improvements afterward is then hardly possible.

Arno schrieb:
...How do you verify the manufacturers’ claims?

By having the building verified and recalculated by an external HVAC engineer. Or you ask the supplier, before signing a contract, to provide a realistic consumption forecast and make this part of the contract after prior verification.

Arno schrieb:
...And what do you mean by the 4l/m² that people have been burned by?

There are various suppliers who advertise using these liters of oil per square meter equivalents. Unfortunately, in many cases, the actual consumption is significantly higher. Taking this into account, the prices of these properties are naturally far too high.

Best regards