I'm thinking of putting a dehumidifier in our bathroom and pehaps blocking up the extractor fan. In summer I would just rely on opening the window.

What about electrical regulations? Will it have to be in a locked cupboard or something. How do other people do it?

Wiring regulations cover fixed wiring and equipment, so they only affect the dehumidifier if it is permanently wired in. You will probably have to do this unless it's a big bathroom, because a socket must be at least 3m from the edge of the bath or shower.

Whether fixed or not, it is still good practice and common sense to position the DH according to its IP (ingress protection) rating as ST says. No IP rating is required if it is outside the zones (i.e. more than 0.6m from edge of bath or shower, or 1.2m horizontally from shower head in a 'wet room' setup). You could put it inside the zones if it has a rating of IPX4 or better (i.e. if the last figure is 4 or more; 'X' means 'any number'), but why would you want to, unless it's a really small room?

This is NOT a full statement of the relevant wiring regs but it should give you an idea. I'm assuming the wiring is RCD-protected.

If your bathroom is big, no problem. If it is small, you might decide it is easier to position the dehumidifier outside the bathroom and leave the door open

Anyone done calculations of the 24 hour energy loss considering the stack effect on a common or garden extractor fan?

Thanks everyone.
I'd want to put it in a cupboard with a louvre door or something to hide it. So if it's permanetly wired in O.6 m from bath or shower is ok. That should be possible. I suppose an alternative would be to run a cable to a socket outside the bathroom which seems like cheating but i guess would technically be allowed?

Yes, hoping it would be an efficient electric heater in winter - I'd only use it when heating would be on.
Even extractor fans that have a closing shutter are still totally uninsulated so not great, including I believe the through the wall MVHR ones which some people on here have said leak air when not in use too.

kitchen below. Probably wouldn't need to be on too much hopefully. Are they very noisy?

Posted By: haplessDiyerthe through the wall MVHR ones which some people on here have said leak air when not in use too.

As gravelld says they'll be exhausting all the time (certainly during the heating season) so can't really leak. What they generally do is have a slight negative pressure to them, so will pull a small amount of air from adjacent rooms.

As an aside, it's difficult explaining that while a dehumidifier will pass the room's air over a cool surface, and the emitted air will feel cool, it does not actually end up cooling the room, but heating it.

That said, it might be possible to combine a dehumidifier with an air source heat pump in order to heat the condensate to 90C such that the heat of the room went down the drain with the humidity. Is such a device only theoretically possible, or does it exist?

MVHR vs a dehumidifier is less than obvious, it depends on your main heating costs:

http://edavies.me.uk/2013/12/dehumifiers/

If a house is completely sealed then a dehumidifier will heat it to the extent of the electricity it uses. The heat released from condensation will balance the heat lost evaporating the water around the house in the first place. Ventilation will lose that (or a proportion of it if there's heat recovery).

interesting Ed about drying washing outside wasting latent heat. I hadn't thought of that!
I guess utilisting the heat of bathwater by letting it go cold in the bath afterwards would be another advantage of a dehumidifier.

<blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: haplessDiyer</cite>I'm thinking of putting a dehumidifier in our bathroom and pehaps blocking up the extractor fan. In summer I would just rely on opening the window.</blockquote>
FWIW, none of our previous houses had any bathroom ventilation except opening windows and we never had any problems. Opening windows for a while isn't a problem, even in winter.</blockquote>

It can be if you have to rush off in the morning and can't hang around 20 mins to shut the window.
Arguable anyway that it opening in winter isn't a problem - surely to release humidity will necessarily mean losing a lot of heat?

Worth mentioning what the background to that calculation was: somebody was stuck in a rented basement flat in London with black mould but absolutely no interest from the landlord in any infrastructure changes. Can't remember if she said what the heating was but she was being advised to heat and ventilate it more hence my suggestion of a dehumidifier.

A gas-burning dehumidifier would need a proper vent. If you're doing infrastructure like that then heat-recovery ventilation would seem to be the way to go.

A bathroom is just about 'the tropics', which is a bit of a misleading term.

I grew up in 'the tropics', very different weather regimes between the East Indies and the West Indies.

<blockquote><cite>Posted By: rhamdu</cite>Ed, that's a very interesting calculation not only from the point of view of cost but of greenhouse gas emissions. If your electricity is generated from gas at 30% efficiency, the dehumidifier uses 2.3kW of gas as against 1kW required for heating and ventilation. The dehumidifier therefore puts 2.3 times as much CO2 into the atmosphere.
</blockquote>

But as Ed says, dehumidifier may win on controlability. Not only is it easy to overventilate on windy days but ventilation will often leak when not in use and even if the shutter is airtight it will still be a cold bridge.