20% humidity in KFW 40+ new construction

Without EWT, the ventilation already throttles at -1° and then eventually shuts off. Unless you install a pre-heating coil beforehand...

This has nothing to do with an EWT, but also applies to normal heat exchangers as frost protection. Rather, the EWT is the problem here because moisture can freeze on the EWT membranes due to the outside air, which can only happen much later with a heat exchanger.

Because all other solutions don’t work as well and passively – quite simply.

Unfortunately, that is complete nonsense and it works millions of times over just in Germany alone.

That's unfortunately total nonsense and works millions of times over just in Germany alone

Yes, if you like humidity levels of 20-30%, that works great. Alternatively, you can water hundreds of plants daily. Or you bring energy-intensive humidifiers with germ problems into the house. Great, really.

This has nothing to do with an EWT, but also applies to normal heat exchangers as frost protection. Rather, the EWT is the problem here since the moisture on the EWT membranes can freeze due to the outside air, which can only happen much later on a normal heat exchanger.

If you have no clue,...

Honestly, what kind of nonsense are you talking about? Normal heat exchangers have to activate frost protection functions from 0 degrees (in the form of preheating coils or mixing in outside air) – EWTs only from -6 to -7° C outside air. That’s a fact. I don’t know what you’re making up there, but it’s not based on facts. Do you have a normal heat exchanger that you have to convince yourself of? If I were you, I’d hold my breath, read up on it, and then come back.


EWTs are also more efficient than normal heat exchangers because the evaporative energy is retained inside the house. Otherwise, you have to remove the energy from the room expensively again via a humidifier or plants.

Like Zehnder:



And Helios:

I don't know what there is to consider about 7000 euros. Some people here act as if a [controlled residential ventilation system] costs 20 or 30k. Whoever doesn't install that in their new building cannot be helped anymore.

Yes, if you like air humidities of 20-30%, that works great. Alternatively, you can water hundreds of plants daily. Or you bring energy-intensive humidifiers with germ problems into the house. Great, really.

So for me, it's not 20-30% but 55% which is regulated without additional humidification.

If you have no clue,...

Honestly, what nonsense are you talking about? Normal heat exchangers have to activate frost protection functions from 0 degrees (in the form of preheating coil or mixing of outside air) – enthalpy wheel heat exchangers only from -6 to -7° C outside temperature. That is a fact. I don’t know what you’re making up there, but it’s not based on facts. Do you have a normal heat exchanger that you have to talk up? If I were you, I would hold my breath, read up, and then come back.

Enthalpy wheel heat exchangers are also more efficient than normal heat exchangers because the evaporation energy is retained in the house. Otherwise, you have to remove the energy from the room again expensively via humidifiers or plants.

Like Zehnder:



And Helios:

What else can I say but stay in your world and that’s fine, it makes no sense...

So for me, it’s not 20-30% but 55% that is regulated without additional humidification

That does not correspond to what I hear as a problem in various forums regarding controlled residential ventilation in winter without EWT.

What else can I say except stay in your world and that’s that, it makes no sense...

Okay, that was maybe harsh. But honest.

You can’t just spread untruths here. That contradicts physics – it is physically very simply explainable why EWT has advantages at cold ambient temperatures. This is not a marketing gimmick from the manufacturers.

We have now ordered an EWT, delivery time unknown. 9% was then the decisive reason... The hygrometer was indeed in the sun, but still. It is still so dry everywhere (20% - max. 30%) despite summer & humid weather.