Green Building Forum - DIY dehumidifier - reality check

DIY dehumidifier - reality check

gyrogear — Sun, 26 Jan 2020 21:27:45 +0000

Mainland cousin says:

"Multi-unit dwelling, owner-occupier: I have a problem siting a bathroom extractor fan -- it can't be in the outside wall or in the window, as they are both over the bath, which isn't allowed. The only alternative is a ceiling-mounted one, which routes through the loft space, and vents in the eaves soffit. However, venting to eaves soffit is a NOK as water vapour could be drawn back into the loft. Also not my loft (even if I do have access to it...). Can't afford the angst of cutting a hole in the soffit viz. neighbour's ratting and hassle from managing agents etc.

Whence flash of inspiration: I have a condensing tumble dryer, which manages to condense the soup from my washing without releasing any moist air into my hall. Putting two and two together, I wondered about buying a condenser to install in the loft, to receive a duct from a bathroom extractor fan. I ended up deciding that it would be worth making one, to see if it works (don't see why it wouldn't!).

So I have bought two 2nd-hand drier condenser units off of ear-bay...

These will need hacking around somewhat, then mount one atop the other, inside a cabinet with a fan pulling air through the fins.

I have ordered an 80mm 240v fan, but think I might need two. Then the unit would be plumbed in so that the condensate drains down through the wall and into the waste pipe in the kitchen.

Sort-of replacement for a commercial dehumidifier, but Â« somewhat far cheaper... Â»

Project guidance appreciated".

via gg.

DIY dehumidifier - reality check

tony — Sun, 26 Jan 2020 21:33:33 +0000

Try to use all the heat that it generates and keep this inside your home at least in the colder months.

Humidity monitoring is going to be essential and if this can control the fan, well and good, if not then a humidistat.

DIY dehumidifier - reality check

gyrogear — Sun, 26 Jan 2020 21:40:36 +0000

Aha, thanks for that, Tony !

So his cabinet needs to be inside his heated volume, and not up in the loft.

Thanks for the feedback !

gg

DIY dehumidifier - reality check

goodevans — Sun, 26 Jan 2020 23:01:46 +0000

Or, alternatively, buy a zone 1 extractor fan that can be located above the bath.

DIY dehumidifier - reality check

djh — Mon, 27 Jan 2020 16:17:44 +0000

Posted By: gyrogearMainland cousin

Sorry, where is 'mainland'? What regs are applicable? In particular, given the regs make some statements about what type of extractor is not permitted, do they say anything about what is required?

DIY dehumidifier - reality check

CWatters — Mon, 27 Jan 2020 19:16:34 +0000

"Multi-unit dwelling, owner-occupier: I have a problem siting a bathroom extractor fan -- it can't be in the outside wall or in the window, as they are both over the bath, which isn't allowed.

Is this in England...

The bath is zone 0, the area above the bath upto 2.25m is zone 1, above that zone 2.

In zone 1 you can have electrical appliances as long as they are rated IPx4 or greater. Must also be RCD protected.

Manrose make IP rated wall mounted fans. I think window fans are harder to find because of double glazing.

DIY dehumidifier - reality check

WillInAberdeen — Tue, 28 Jan 2020 10:26:10 +0000

GG, the airflow through a bathroom fan is about 1m3 every minute, each m3 contains about 20g of water vapour when saturated. So that's lots of grammes of water to condense every minute.

Gut feeling is that a tumble dryer doesn't condense that much water that fast. So the extracted air would still be quite damp when it is discharged into the loft. Maybe your cousin could recycle the air back into the bathroom, then run the fan for a period after showering, so the air gets gradually drier, after several passes through the condenser?

Few other thoughts
-mains electric and water and bathrooms don't mix well, could he use SELV as GE suggests

-damp and lofts don't mix well either, the managing agent is quite correct

- the regs are different in the Scottish and English mainlands and islands, but both have requirements about electrical safety and avoidance of damp decay

- tumble dryer condensers don't recover heat, they dump it into the outgoing air stream (to dry the clothes more) - re-siting the box will not help this

- extractor fans have an important function the morning after curry night

Your cousin should consider a MHRV fan professionally installed and ducted through the loft to a soffit or tile vent