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Comment by tvb12 | Hacker News Reader

> "The unit has produced a public awareness film urging people to ventilate their homes properly by ‘keeping vents or windows open when cooking, showering and cleaning..."

Why showering?

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The other two are to exhaust CO2, fumes and particulates, but I presume that the note about showering is for removing moisture from the interior air and preventing mold growth.

Ideally you want external exhausting vent fans in every kitchen and bathroom, although lots of places have nothing at all or only internal vent fans.

I assume, steam causing moisture build up and associated mould and rot. That's a problem easily solved with a $20 exhaust fan though.

The cost of the fan is dwarfed by labor, and you’re not getting a fan you want to live with for $20. Also, at least in California, you have to hook it to a janky humidity sensing switch that costs more than $20.

> Also, at least in California, you have to hook it to a janky humidity sensing switch that costs more than $20.

To make it run automatically?

To have your tight house (and your family) breathe properly you’ll want to couple your smart bathroom exhaust fans with filtered air intakes. HRV/ERVs can do this but are overkill in many mild climates. A set of simple fan+filter pairs does the trick for us, can’t believe we lived so many years in poor ventilation.

> humidity sensing

Anyone have links to working designs for humidity controlled fans or similar - preferably Raspberry Pi?

I want an indoor sensor and an outdoor sensor, and to run the fan only occasionally (maybe 10 minutes a day) and only when outdoor humidity is much lower then indoor humidity. For holiday sleepout, that sometimes gets damp, but outdoors is sometimes high humidity so no point running fan in that case!

I've looked at household ducted fans, but they don't really do what I want.

BME680 sensors for temperature/humidity/pressure should be suitable. Consider the PI's PWM output and a hobby RC BLDC motor/controller combination for "cheap variable-speed fan", or alternatively, a large diameter PWM computer fan from e.g. Noctua. Depends on the power class you need/want to go for (PC fan is low power, RC BLDC is high power).

I'm just talking about a normal bathroom fan you turn on when you want to have a shower or something. I've honestly never seen one at a hardware store that costs more than about $40. An electrician would take about 15 minutes to install one if you've got a power source nearby, or if you get one with a light built in you could install it yourself by just replacing an existing light fixture with it.

Luckily I don't have the misfortune to live anywhere near California, but that humidity sensor business sounds bizarre. Is that some kind of building-code thing?

If you have an exhaust fan on to remove shower steam, the air needs to come from somewhere. You don’t want it getting sucked in through the walls (bad air quality). Better to open a window.

No. You need a fan+filter to exchange the air.

Why cooking? Only minority of people in developed countries cook on gas nowadays.

Depends on the country.

Australia for example has a high amount of gas usage for cooking.

It's not only when cooking on gas. For example, if you sear meat, you will emit lots of particles that can be harmful to health.

Technically a minority, but 40% of homes in the US cook with gas.

Regardless of the method, boiling water puts a lot of moisture into the air.

Lots of humidity can be bad in a humid climate.

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