ᐅ Air Too Dry! – Should I Replace My Old Ventilation System with an Enthalpy Recovery Ventilation System?
Created on: 12 Oct 2025 21:10
H
Hendrik1980
Dear forum,
We have been living in our well-insulated KFW55 house with a controlled mechanical ventilation system for 2 years now. In winter, the indoor humidity sometimes drops to as low as 20%. I would like to change that!
Unfortunately, our current controlled ventilation system does not include an enthalpy heat exchanger, and it is not possible to retrofit one. Therefore, we are considering replacing the ventilation system. This would cost around 5,000 euros.
Is the effort worth it? Can we expect the indoor humidity to increase significantly after the replacement? What humidity levels can we roughly expect following the upgrade?
We have been living in our well-insulated KFW55 house with a controlled mechanical ventilation system for 2 years now. In winter, the indoor humidity sometimes drops to as low as 20%. I would like to change that!
Unfortunately, our current controlled ventilation system does not include an enthalpy heat exchanger, and it is not possible to retrofit one. Therefore, we are considering replacing the ventilation system. This would cost around 5,000 euros.
Is the effort worth it? Can we expect the indoor humidity to increase significantly after the replacement? What humidity levels can we roughly expect following the upgrade?
R
RotorMotor13 Oct 2025 20:17It's always amusing how the same people keep spreading the same "truths."
Slike always talks about how great it is to make the air more humid by ventilating, while Wiltshire says you should just plaster some clay on...
How about we wait for the basic information from the OP and solve this based on facts?
Slike always talks about how great it is to make the air more humid by ventilating, while Wiltshire says you should just plaster some clay on...
How about we wait for the basic information from the OP and solve this based on facts?
Hendrik198013 Oct 2025 21:09Dear forum,
thank you for your many responses!
Currently, we have a Wolf CWL 300 installed, and our HVAC contractor has suggested replacing it with a CWL-2-325 enthalpy unit.
At this point, I cannot imagine having the house replastered. We live here with two small children, so that effort seems disproportionate to me.
As far as I understand, my ventilation system can only operate in 4 levels (0 moisture protection, 1 reduced ventilation, 2 nominal ventilation, and 3 intensive ventilation). Right now, it runs in automatic/timed mode between 7 a.m. and 7 p.m. on level 2 (160 m³/h (94 cfm)). At night, it switches to reduced ventilation (150 m³/h (88 cfm)).
We have not yet tried using humidifiers, laundry drying, etc., as I was hoping that with the enthalpy unit, we wouldn’t have to manage air humidity "manually."
Perhaps I should try to reduce ventilation even more during the winter. However, it seems that in auto mode I can only adjust the times for levels 1 and 2, but I do not have the option to switch to moisture protection at night... I will discuss this again with my HVAC contractor...
thank you for your many responses!
Currently, we have a Wolf CWL 300 installed, and our HVAC contractor has suggested replacing it with a CWL-2-325 enthalpy unit.
At this point, I cannot imagine having the house replastered. We live here with two small children, so that effort seems disproportionate to me.
As far as I understand, my ventilation system can only operate in 4 levels (0 moisture protection, 1 reduced ventilation, 2 nominal ventilation, and 3 intensive ventilation). Right now, it runs in automatic/timed mode between 7 a.m. and 7 p.m. on level 2 (160 m³/h (94 cfm)). At night, it switches to reduced ventilation (150 m³/h (88 cfm)).
We have not yet tried using humidifiers, laundry drying, etc., as I was hoping that with the enthalpy unit, we wouldn’t have to manage air humidity "manually."
Perhaps I should try to reduce ventilation even more during the winter. However, it seems that in auto mode I can only adjust the times for levels 1 and 2, but I do not have the option to switch to moisture protection at night... I will discuss this again with my HVAC contractor...
Hendrik198013 Oct 2025 21:17There is an error: it should be 220 m³/h (130 cfm) at level 2.
R
RotorMotor13 Oct 2025 21:26Hendrik1980 schrieb:
Currently, a Wolf CWL 300 is installed, and our heating/plumbing service suggested replacing it with a CWL-2-325 enthalpy unit. You can find enthalpy exchangers for the CWL 300 (Excellent?). Prices range between 600 and 1200€ (approximately). I would just buy and install one.
Before that, definitely double-check the exact model number!
A completely new CWL-2-325 seems unnecessarily expensive to me.
How old is your CWL 300?
Hendrik1980 schrieb:
As far as I can see, my ventilation system only operates in 4 levels (0 moisture protection, 1 reduced ventilation, 2 nominal ventilation, 3 intensive ventilation). Currently, it runs in automatic/timed mode between 7 a.m. and 7 p.m. at level 2 (160m3/h (5600 cubic feet per hour)). At night, it switches to reduced ventilation (150m3/h (5300 cubic feet per hour)). That can be configured!
Each level can be set between 50 and 300 m3/h (1800 and 10600 cubic feet per hour).
Hendrik1980 schrieb:
We haven’t tried humidifiers or drying laundry indoors yet, because I hoped that with the enthalpy exchanger, we wouldn’t have to manually manage air humidification. But you don’t actually have an enthalpy heat exchanger.
Before spending thousands on one, you might want to try a few other things first.
W
wiltshire13 Oct 2025 22:18RotorMotor schrieb:
It’s always entertaining how the same people keep spreading the same “truths.” I almost expected you to respond like that.
Inform yourself before mocking others and just check the facts. You can find a report from 2004 at the Fraunhofer Institute for Building Physics or, if you don’t consider them reliable enough, consult DIN 18947, which categorizes water vapor absorption classes WS-I to III. The University of Bath (Moisture Buffering Capacity studies) and the University of Vienna (publications on sorption and diffusion measurement data) have also released scientific papers on this topic.
This should be easy to find with that description.
This is not about “opinions” or any stories about “breathing walls.” This is about established facts.
The water vapor absorption properties are well researched, part of standards, fundamental in building physics, and these properties are measurable and can be calculated.
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RotorMotor13 Oct 2025 22:34So, if someone complains about permanently dry air with 20% humidity, clay simply won’t help at all!
Clay can moderate humidity levels, yes, but nothing more. That’s what the studies and standards say.
Maybe you should read (and understand) them?
That means if someone here soon complains about fluctuating humidity, feel free to spread some clay somewhere for them...
Clay can moderate humidity levels, yes, but nothing more. That’s what the studies and standards say.
Maybe you should read (and understand) them?
That means if someone here soon complains about fluctuating humidity, feel free to spread some clay somewhere for them...
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