Dehumidifiers

I was wondering if using a dehumidifier in the workshop will be expensive to run? The workshop is around15ft square. I am currently insulating the flat
roof with fiberglass and plasterboarding it out. There will be airspace above the insulation for ventilation. I need to seal around the up & over door. Windows are double glazed. Two walls are 4" breezeblock, the others are single brick. The floor is concrete. I don't expect the workshop/gargage to be at room temperature at anytime as I can put up with a little cold. What I need to do is keep humidity down to stop everything going rusty. Do dehumidifiers work down to freezing? Do they have any defrost functions to keep the workshop from freezing? Would just a dehumidifier work to keep things from going rusty? Would it have to be on all the time? What sort of power do they take ? Are they expensive to run? I can't afford an expensive dehumidifier, so would a cheapish (150) one be okay? Any suggestions would be greatly appreciated.
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They take about a kWhr/gallon of condensate if they are working as well as possible. Rather worse as the air gets drier and colder. rated power for a 15l/day one is likely to be about 200W. They generally won't work well below about 10-15C but in a well sealed shed, the waste heat they generate will raise the air temperature somewhat anyway. If it doesn't have automatic defrost, don't buy it. Decent ones will have it. I've used them to keep the metal worm out of a concrete section/asbestos cement roof garage and not stressed too much over the cost. The better sealed and insulated the space is, the lower the cost. It can be worth running the drain outside with some garden hose, or chocking the unit up on blocks and draining to a bucket. When starting off, you can pull quite a lot of moisture out of the concrete. After a wile it will settle down.
They are a better bet than any form of electrical heating because you are getting useful work out of the electricity as well as plain heat. Bear in mind that a domestic unit is likely to crap out after a couple of years. Normally the air moving fan will fail because the manufacturers can't be bothered with ball bearings. This is not an issue for anyone of an engineering bent :-).
For 15ft square, the smallest capacity decent (fridge type, not thermal adsorption type) one you can find will probably be fine. set it to whatever they class as a normal level or a bit drier and just leave it to cycle on and off.
Mark Rand RTFM
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I think the smart point above is to use the de-humidifier waste heat as the sole source of heating. I've found if you get the workshop get toast warm on a cold winters night, even the metalworm drowns. Never use gas heating...
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On Sat, 4 Oct 2008 10:06:59 +0100, "Steve"

...unless your gas heater has a flue (vented to the outside, of course).
Regards, Tony
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wrote:

Veryup market, having a flue...
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wrote:

...ordinary mortals just catch cold :{
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Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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Many thanks for everyone's help regarding de-humidifiers. I'm fairly happy about the insulation side of things, particularly the roof space. What was really worrying was the cost of running a dehumidifier 24 hours a day. In the end though, I don't have a lot of choice but to buy and run one if the workshop/garage is to become rust free. With respect to the de-frost function .... can I assume if I bought one with de-frost, it will virtually look after itself ? i.e. just leave the machine on and if the temperature gets down to freezing, the de-humidifier will automatically switch back on when the air temperature rises to the operating temperature? Cheers Dave
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wrote:

Bear in mind that, once you have the humidity down to a reasonable level, they don't run for anything like 100% of the time.
Tim
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Can you leave them on 'automatic' so they look after themselves? Dave
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We have a small commercial unit at the workshop, it extracts about a gallon a day in wet weather conditions, or that amount a week in dry. It has an internal reservoir with a float cut-off when it is full.
It's been in place since March last year and runs 24 hours a day everyday.
No problems so far, there is no damp course in part of the building so we do get a fair bit of damp in if we don't run the machine. Waiting for the landlord to do summat about it!
I think we bought it on ebay IIRC, but can check the details if anyone want to know.
We also bought a dust extractor at the same time, which runs 24/7 and takes a lot of cr*p out of the air which keeps the place cleaner. That was well worth the money as well. Filter is changed about every three or four months, but we give it a brush and a shake every few weeks.
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk http://www.oldengine.org/members/diesel http://www.stationary-engine.co.uk http://www.oldengine.co.uk
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I used to dehumidify my garage with a basic (cheap) domestic model. I discovered it did not have a frost cut-off when it turned itself into a block of ice one cold spell. A thermostat, cost me abt 8 IIRC, wired to call for cool rather than heat, and set at 7degC, fixed it.
John
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"John Nice" <johnDOTniceATbtinternetDOTcom> wrote in message

Don't forget that if you want to leave it running 24/7 you have to provide a drain for the condensate to the outside world. Mine has a trip switch which shuts it off when the reservoir is full.
Also remember it will dry out every piece of wood in the shop. I installed mine when the workshop was new and still a bit damp. Left it running and emptied reservoir daily until I realised my woodworking bench was starting to crack and so was most of my stock of timber. Nowadays run it about 1 day a week and its fine.
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Ah, that is a point worth thinking about. I have 2 large wooden benches and the roof is all timber (although it will be insulated very soon). Just wondering about the dehumidifier's effect on plasterboard once it is put up on the ceiling ??? I'm not going to skim it out as it is only a workshop/garage. Does anybody think that it will damage the plasterboard by reducing the humidity too far?
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Most of them have a "humidity" setting which under given conditions will determine the duty cycle, i.e. the electricity consumption. You probably don't need to have it too high. The other downside of cheap ones is that they are fairly noisy.

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On or around Sat, 4 Oct 2008 00:21:49 +0100, "Dave"

It would in mine, bloody machines were soaking with condensation this ack emma.
However, there are mertis in never cleaning them properly, the resultant oil and so forth all over it makes it less prone to rust :-)
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