Construction costs are currently skyrocketing

Interesting topic. Can anyone actively report on something like this? I mean subsequent checks by the KfW.

Yes, it happened to our energy consultant a few years ago. Basically possible, but in his experience randomly at 0.x%

There is a difference between exhaust air without heat recovery and ventilation with heat recovery. In the first case, the heat stays inside and the moisture goes out, in the other both go out. And now we can do a little calculation. Heating 1cbm of air by 1 degree requires 0.33Wh. With a 20-degree temperature difference and 500cbm air exchange, 3.3 kWh of heat energy is lost through the exhaust hood. With recirculation hood and ventilation with 80-90% heat recovery, only a fraction of that is lost. In grandma’s unrenovated little house from 1965 with 250 kWh/sqm that doesn’t matter. In new buildings, it does.

The warm indoor air is pushed outside in both cases... where is the difference?

The difference is that, because of the moisture sources you mention, I do not ventilate. That is done by the controlled residential ventilation system, and my living/dining/kitchen area is 55 sqm in size. Nobody gets foggy glasses from a boiled-down soup there :)

We still haven't found an affordable tiler and have now turned to the platform with the hammer. So far, received one concrete offer....for 37m2 with skirting boards offered just under 5000 EUR, which is even more expensive than what we have been offered so far^^. But it is quite easy to get in touch with interested companies, which is definitely an advantage. My expectations are around 3000 EUR, is that really that low?? I actually think it's fair for both sides.

There is a difference between exhaust air without heat recovery and ventilation with heat recovery. In one, the heat stays inside and the moisture goes out, in the other, both go out. And now we can do some calculations. Heating 1 cubic meter of air by 1 degree requires 0.33 Wh. With a temperature difference of 20 degrees and 500 cubic meters of air exchange, 3.3 kWh of heat energy are lost through the exhaust hood. With a recirculation hood and ventilation with 80-90% heat recovery, it's only a fraction of that. In grandma’s uninsulated house from 1965 with 250 kWh/sqm, that doesn’t matter. In new buildings, it does not.

And how do you come up with the 500 cubic meters? I’d have to run it full blast for a whole hour. In reality, full blast runs for a maximum of 10 minutes during a frying process, and even then only for red meat or the famous herrings. With a short pre-run and a somewhat longer post-run. And you have a 20°C difference during cooking times at what percentage of the heating season? Let me be very(!) generous and assume 0.5 kWh heat loss per cooking process during the heating season. In reality, it will be even less, arguments see above. Cooking daily on 120 days per year then makes 60 kWh. I recover half of that alone as waste heat from the stove. The rest is produced in the new building with an annual performance factor of 3. That is, sorry for the expression, a drop in the ocean. People just make good money on recirculation systems.

And how do you come up with the 500cbm?

That was from the 500cbm per hour and because it’s so easy to calculate in your head. It’s clear that you don’t run it at full power for an hour. But the fact remains that a range hood is designed for about 10 air changes per hour, which is quite a lot.

And 20°C difference do you have during cooking times at what % of the heating period?

Not exactly our place of residence, but nearby and at a similar altitude

I have a 20 degree difference on average for 3 months, plus almost as much in March and November. That is probably the entire heating season for us. At the latest from April, the heat pump should only be needed for hot water, probably much earlier.