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Comment by mrngld | Hacker News Reader

Do you have HVAC? Maybe some of my difficultly understanding is being American I'm in a hotter, much more humid climate, so we've got central HVAC. A key feature of heat pumps isn't just that it lowers the temperature of the air, it also reduces humidity.

I've got a lot of exposure to new home construction here and can tell you I don't even know what "damp proofing" is, and our bathrooms don't need special paint. They're ventilated and we have HVAC. Beyond that, if homeowners take 30 minute showers with scalding hot water and the door closed then, well, the outcome is inevitable no matter what you do. Not just mold but you'll start damaging fixtures, etc.

It's hard to get old caulking clean and keep it mold free, just gotta recaulk regularly, but I'm somewhat skeptical of blaming paint.

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> Maybe some of my difficultly understanding is being American

In the UK, in winter, ambient exterior air is both fairly cold (let's say 40F) and extremely humid, often around 80% relative humidity.

Houses are both poorly insulated and poorly ventilated. Heating is (relatively) very expensive.

Most housing units don't have clothes dryers, and it's common to dry clothing indoors on wire racks.

The net result is that you end up with extremely humid indoor air in the 55F-65F range, while the exterior walls and windows of the building never really heat up properly.

It's a recipe for condensation on the interior surfaces of those walls and windows.

You can fix this either by heating the building enough that the exterior walls actually heat up beyond the dew point (which few people can afford to do), or by keeping windows open in winter to provide some ventilation (which makes the already-poorly-heated building even less comfortable).

No, I've never seen a residential house with HVAC, even in big apartments. It's all split wall mounted AC units here, or if you're fancy a ceiling version that's basically the same. I think Americans call these heat pumps?

Split AC systems remove moisture from the air when they’re running too, that’s why there’s a condensate drain on the evaporator (and the condenser, but that is outside).

They remove a small amount of moisture, yes. It's nothing compared to what a dehumidifier removes though, even if they're in dry mode.

A condensate dehumidifier is just an air conditioner where the condenser is inside the same space as the evaporator. It uses vapor compression refrigeration.

Granted, the condenser and evaporator both condensing moisture inside of the space does remove more moisture so you’re correct about it being more effective, but an A/C unit does a pretty good job where I live, and cooler air holds less moisture.

I never deal with cold and damp conditions, a dehumidifier probably works well in the UK. I’ve lived in forced air and radiant heated buildings and they both dry out the air like crazy in the winter so dehumidification isn’t needed, humidification is.

It's probably relative to how much humidity there is where you are. I'm in a very humid area, and I have humidity sensors. Leaving an AC unit on dry mode in a small room does basically nothing - at most it will shift humidity by a few percentage points. Meanwhile if I use the actual dehumidifier I can drop from 85-90% down to 65%. If I turn the machine off for a few hours (or move it to another room) it'll be back up in no time.

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