Dehumidifiers

[Peter]

I've been considering getting a dehumidifier for my mum's Christmas.  It's almost impossible to dry clothes outside for much of the year, so she relies heavily on an old tumble drier and hanging clothes in the small bedroom with the radiator on and the window open to minimise the moisture that gets into the house, but it still gets quite humid in there, and it must cost a lot to have radiator pumping heat out the window.  The house is quite damp generally, and I occasionally have to scrub mould off the walls with bleach, and the air always feels noticeably damp and often quite cold from it.  Also, the window for the bathroom is often open since there's no extractor, and for some weird reason, the central heating system requires that radiator to be constantly on in order for it to work, so that's another major source of heat loss.

Should I get her a dehumidifier?  What's the best sort of dehumidifier to get?  Should I get the refrigerator sort, or the desiccant sort?  Some manufacturers are claiming that their dehumidifier is cheaper for drying clothes than a tumble drier, but is this true?  Most dehumidifiers that I've seen use upwards of 0.5KW when they're on, but what's a typical duty cycle, and how much would it cost to run?  What size of dehumidifier should I get?  It's a 2 story house measuring 5.5m X 7.6m, so it has 83.6 square metres (896 square feet) of floor space, and with a total volume, as measured from floor to ceiling, of 105 cubic metres (3721 cubic feet).  The problems are mostly upstairs though, so the downstairs doesn't need dehumidified.  Should I get one that has air filters and things?  Most of the higher end ones I've seen have some air purifying functions in addition to dehumidifying.

[garmonbozia]

I've owned three portable dehumidifiers over the years, and they've all been a pain in the ass.  I've still got the last of the three, but instead of using it right now it's in the storeroom.

If you're willing to put up with a few things, they'll definitely suck the air dry and cut down on mold.  Here's what you've got to put up with...

1) heat... lots of it.  I tried to use one to keep the bathroom from fogging up and growing mold, but it also warmed it up in there.  The humidity would make you sweat, but so does the heat from the thing.  I'm in Florida, so this is a real bitch in the subtropical climate here.

2) de-icing.  The heat from the dehumidifier might be a plus if you're in a colder climate and the room you're going to put it in is chilly anyway, but the trouble is getting the room up to temperature so the coils don't ice up.  Get one with an automatic de-ice cycle.

3) cleaning the coils.  You've got to do that every couple of weeks.  I'd recommend getting a scrub brush just for the dehumidifier.  If you can get one with an air filter, that should help keep the coils from clogging up with dust and lint and crap.

4) emptying the bucket.  Most dehumidifiers have a connection for a drain hose, and if you're lucky, you can find a place on a shelf where you can run the drain hose by gravity into a sink.  That condensate gets really nasty, by the way, so don't try to re-use it for anything.  If it's on a shelf, you still have to make sure it's got room to circulate air and vent off its heat, and also that it doesn't "walk" off the shelf due to its own mechanical vibrations and crash onto the floor.

The above tips apply only to the portable, refrigerant-type dehumidifiers.  You mentioned you've got a two-story house.  Is the dehumidifier for the entire house?  If so, you might want to invest in the kind that hooks up to your central air system.

As for the dessicant kind...  Are you talking about Damp Rid and similar systems you can get at the grocery store?  Those make a nasty chemical goo that you've got to empty out periodically, and are really just for confined spaces like closets, cabinets, etc.

Hope that helps.

[Peter]

1) heat... lots of it.  I tried to use one to keep the bathroom from fogging up and growing mold, but it also warmed it up in there.  The humidity would make you sweat, but so does the heat from the thing.  I'm in Florida, so this is a real bitch in the subtropical climate here.

2) de-icing.  The heat from the dehumidifier might be a plus if you're in a colder climate and the room you're going to put it in is chilly anyway, but the trouble is getting the room up to temperature so the coils don't ice up.  Get one with an automatic de-ice cycle.

The dampness and humidity are worst in the 11 months of the year that aren't summer, so heat is unlikely to be an issue, but cold might be.

The above tips apply only to the portable, refrigerant-type dehumidifiers.  You mentioned you've got a two-story house.  Is the dehumidifier for the entire house?  If so, you might want to invest in the kind that hooks up to your central air system.

We don't have a central air system; the house was built in the 1930's, and I don't think they had those back then.  It'll only be needed for the second story, since that's where the problems are.

As for the dessicant kind...  Are you talking about Damp Rid and similar systems you can get at the grocery store?  Those make a nasty chemical goo that you've got to empty out periodically, and are really just for confined spaces like closets, cabinets, etc.

Hope that helps.

I know the ones you mean, but I was talking about this sort, which dry out their own desiccant and recover the water in a tank like coil dehumidifiers do.

[SovaNu]

i think get a dehumidifier. yep. those rotting corpses in your walls would stink less.

[Soph]

we used to have one of them. all i remember was it could be noisy. i think it was good though.

[Calandale]

Had one in the basement.
Used to pull a bucketfull of
water out a couple times
a day.

[garmonbozia]

Some even have built-in pumps, so you can still connect them to a drain even if there isn't a high enough shelf to put them on.

[Peter]

I found this calculator.  It says that the indoor relative humidity in this house is 60% at the moment, based on 10C outdoor temp, 94% outdoor relative humidity and 17C indoor temp.  That's apparently the perfect relative humidity level for dust mites and mould to infest the place.  Also, refrigerant dehumidifiers are supposed to be very inefficient when the dew point is below 10C, so it'll have to be a desiccant dehumidifier.