[littlestymaar]

Then it just means that you're overventilating! We emit much more steam (through cooking and showering for instance) than we consume oxygen/emit CO2 so controlling the humidity is the main purpose of ventilation, air renewal comes for free as a byproduct of that.

[manmal]

My system doesn’t over ventilate - we sometimes have too high CO2 in the bed rooms, but humidity is way too low in winters, sometimes below 30%. That means getting sick more often and having irritated airways at times.

[cwillu]

For reference, it is currently 84% relative humidity and -20°C outside where I live. This is about the same absolute humidity as 5% relative humidity at 22°C (i.e., inside).

[littlestymaar]

An all you need to bring that up to above 50% is 2cl/cubic meter of water!

A sponge drying up in your kitchen sink is enough to raise your kitchen's air humidity by 10%. Shut down your ventilation and you'll see, you won't suffocate but instead you'll get mold starting to pop-up. Moisture is the reason why houses have ventilation system in the first place.

As I said elsewhere in this thread, though, there's a problem with “dumb” ventilation systems though: they can't really adapt to big variations in outdoor conditions, and as such they tend to suck way too much air out of your house than needed during the cold days.

[crazygringo]

> A sponge drying up in your kitchen sink is enough to raise your kitchen's air humidity by 10%.

That's simply not correct.

I go through liters of water a day with my two humidifiers just to try to raise humidity by around 20 percentage points. In a small urban apartment that isn't much bigger than some people's whole suburban kitchens.

A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.

Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.

[littlestymaar]

> I go through liters of water a day with my two humidifiers just to try to raise humidity by around 20 percentage points. In a small urban apartment that isn't much bigger than some people's whole suburban kitchens.

No surprise, that's because your water gets vented away…

My brother had a broken ventilation for a whole northern England winter in a flat he rented (and the landlord was too busy fixing this shit up), he had massive humidity issues with fungi spores making him sick before he understood what the problem was, and he'd tell you how much discipline it takes in manually venting your house by opening the windows to keep things from molding!

> A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.

Hey you know what, just do the math by yourself, it's just one pV = nRT away ! But of course, this is assuming you're not removing all that water directly as it evaporates.

> Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.

Maybe have a look at your local building code and see how the ventilation requirements are made. I've refurbished a house by myself and I did just that, it turns out the regulations are built on water extraction, as CO2 won't realistically kill or harm you, CO only matters in kitchens if/where you have gas stove (and in my country, this is subject to additional ventilation requirements in the kitchen itself independent of the house's ventilation), and VOC are only a recent concern. That's also why there have been hygrometer to pilot ventilation for a while.

[wilted-iris]

I have not observed this to be true. Ventilating enough to keep CO2 low means sub 20% winter humidity in multiple places I’ve lived.

[RGamma]

Even with our cross counterflow enthalpy exchanger it can get somewhat dry in the bedroom in winter. The device in the OP would probably require an additional humidifier.

[szundi]

The less co2 you have the less effect of air exchange does have. Also more co2 in air also decreases this over the decades.