Dehumidifier for the attic

Not sure what type ours is but the biggest problem our friend had when they borrowed it to dry out a room after the bath above was left running overnight was that it kept filling the collecting tank and stopping. Not sure how much water you will be pulling out of the attic or how often you want to go up to empty it. I must admit that it hasn't been a problem I have noticed. The unit we have is a cheap one about 10 years old if that helps work out what type it is.

We've two meaco dd8l...both now probably 10 years old and still running fine despite daily usage. Deccisant type but not significantly more expensive than condenser plus knock out a bit of warm air. Depending on the setting probably empty them maybe 1 or twice a day. Could use a tube attachment though for continuous emptying

The Meaco ones sound pretty good, but don't have an app unfortunately, which would be handy for keeping an eye on it without having to keep going up to the attic and introducing a slug if warm air every time.  I'll fit a drain hose so hopefully can just leave it be.

You'll want a desiccant one if it's a cold loft, refrigerant ones are more efficient at room temperature but performance falls off a cliff below about 15c.

I would got one with a humidistat, set it at 60% to start with. Personally I'd monitor it with a wifi energy monitoring plug, e.g. Tapo P110. If it's not using too much energy at 60% then you can drop it down to 50% or 40%.

edit- here's a couple of shots from mine, it's actually in my hallway but the same idea. You can see from the graph how often it's actually running and how many KWH it's using per day/month etc.
[url= https://i.postimg.cc/WdpcHsPg/Screenshot-2023-12-04-09-16-03-83-c8ce049e2765335b474bc4d710ac1b2a.jp g" target="_blank">https://i.postimg.cc/WdpcHsPg/Screenshot-2023-12-04-09-16-03-83-c8ce049e2765335b474bc4d710ac1b2a.jp g"/> [/img][/url] [url= https://i.postimg.cc/qgnrtmLh/Screenshot-2023-12-04-09-16-06-98-c8ce049e2765335b474bc4d710ac1b2a.jp g" target="_blank">https://i.postimg.cc/qgnrtmLh/Screenshot-2023-12-04-09-16-06-98-c8ce049e2765335b474bc4d710ac1b2a.jp g"/> [/img][/url]

Like everyone else I’m suffering from condensation in the attic again.

Err, no.
If you have condensation in your loft, using a dehumidifier is nothing other than a short term fix - an essential one.
Invest time and money in identifying the problem and take steps to resolve it for a permanent fix.

Invest time and money in identifying the problem and take steps to resolve it for a permanent fix.

This.

frankconway

Err, no.
If you have condensation in your loft, using a dehumidifier is nothing other than a short term fix

To be fair to the OP, that is exactly what he said.

Mowgli

I have a plan to sort the ventilation and have hopefully fixed some warm air leaks, but in the short term I need to suck some water out.

stumpy - my post was more to do with the 'like everyone else...'

Yep as per Multi21, desiccant type is what you need in a cold environment (anything less than room temp).  The refrigerant ones will either simply not work or take ages to extract moisture or increase power consumption.

A lot of the energy consumption figures quoted by manufacturers are in ideal conditions ie air temp around ~20degC etc … so unrealistic for your loft.

If left permanently on in the loft you’ll need one with a drain hose and built in humidistat so you can set it and forget it.

Meaco, Pro Breeze and Eco Air  are brands that get good reviews in Which.  Don’t think there’s much between them.  So get the one with the best deal / discount.

I've got both and indeed the desiccant is more expensive to run. The refrigerant one works fine until you get temps around or below freezing outside (so inside below 15-14 degrees). TBH I just use the refrigerant one all year because the number of days the temp in the house is below 14° aren't often. If it's short term in the winter in the attic then probably get a desiccant with a tank as big as possible so you don't have to keep emptying it. If all year round then refrigerant.

I've got the Zambezi desiccant one and it's excellent but tank is a bit small

Not sure what type ours is but the biggest problem our friend had when they borrowed it to dry out a room after the bath above was left running overnight was that it kept filling the collecting tank and stopping.

I think many of them have an external hose you can use for continuous running, so you can just feed it into a bucket or whatever. I would have thought any decent size one would be fine for overnight though.

Not attic, but used a dessicant one in a damp, cold garage and it was awesome.

Sorted the ventilation out and didn't need it again.

They vibrate a fair bit (our cheap screw fix one that’s several years old does anyway) so unless you’ve a lot of sound damping, you’ll likely hear when it gets full and cuts off. 

They vibrate a fair bit

Have you tried to locate the source of the vibration?. Mine have from time to time, but I could always silence it, sometimes it's maybe the moving Louvre that's resonating or the unit isn't on a flat floor or something.

Be warned that running a dessicant dehumidifier for a significant amount of time can get expensive.

We use a meaco dd8l and I can clearly spot the month we bought it from the electricity bills.

At current electricity it costs around £4 to run for 24 hours, so £120/month.

zntrx - What mode/speed is that in? I just bought one and know it will cost a bit to run. Only used it for a couple of hours at a time so far but at the washing setting or high fan, thanks

Extract your humid air at source (bathrooms and kitchen primarily) and get some air flow in the loft. You don’t want holes through your ceiling letting warm damp air through. Recessed down lights, badly fitting loft hatch, holes around pipes cables and soil vent etc. dehumidifier in loft isn’t really a solution.

What mode/speed is that in?

It's a Meaco Zambezi DD8L at speed 2. This uses around 600W. Speed 1 uses half but extraction is half also. Speed 3 uses slightly more.

For drying clothes it's best if you can set it up in an enclosed space. We have a curtained off alcove 1m x 2m × 2m. When running in thete the temperature gets up to 27C just from the heat from the dehumidifier and the clothes dry pretty quickly (3 - 4 hours).

Thanks

Be warned that running a dessicant dehumidifier for a significant amount of time can get expensive.

We use a meaco dd8l and I can clearly spot the month we bought it from the electricity bills.

At current electricity it costs around £4 to run for 24 hours, so £120/month.

This comment scared me enough to prompt me cough up £7 for a usage monitor plug to work out how much mine was costing me.

Mine is a Pro Breeze Desiccant model. It is on all of the time in my cellar with a continuous drain, set to target a humidity level of 55%, to achieve that is seems to run about half the time.

Anyway, after a day of use it has gobbled up 3.12 kWh. On my Octopus Go tariff I work that out as being £0.77 per day, £23.46 per month.

Temp/humidity graph in my cellar from yesterday. You can see it 's on/off in roughly equal amounts, which is typical.

Think I'm going to need one for my summerhouse, anyone got any running cost figures for that sort of application?

It's un-heated so there's the tendency for any air getting in, to then get cold overnight and condense, then even if the air is circulating it's not warm enough to dry it out again. Back of a fag packet says that's upto about 500ml/day assuming 2 air changes and a 15C temperature swing (windows currently left open as an experiment so more ventilation won't help, and the intention would be to run the dehumidifier with the windows closed).

Previously it had a problem where the base doesn't have any ventilation as it's framed on all sides, so any moisture sat on the concrete was:
a) making the underside of the floorboards moldy
b) breathing through the floorboards and condensing under furniture and particularly under the rubber gym matting
Hopefully resolved that by taking up the floor and adding a layer of superquilt, slightly crossing fingers that the treated wood survives.

@timmys what sensor/app are you using for that graph? I also went for the ProBreeze which is now happily chugging away in the loft. Would be good to see what's going on up there without having to keep opening the (well sealed) hatch.

what sensor/app are you using for that graph?

It's Tado temp monitor, so part of my heating system. I don't actually have any radiators in the cellar but use a spare monitor to keep an eye on it.

I actually just put one up in my attic as well and it's reporting a temp of 7 deg C and 83% humidity at the moment. I really need to take the time to understand relatively humidity to see if that's something to worry about - particularly as I have a PIV pumping "dry air" from the attic around the house. The cold air being pumped out by the PIV was annoying me so I actually turned it down a few days ago. The windows were a lot more damp in the mornings when the PIV was turned down, so it does give me faith it's still doing something useful even when the 'dry' air it's shifting into the house it >80% humid. PIV is now turned back up.

Ironically I have just returned from Costco with one of these:

https://www.costco.co.uk/Appliances/Cooling-Air-Treatment-Heating/Air-Treatment/Woods-10L-Dehumidifier-MDK11-for-rooms-50m-538-ft/p/342983

I had never heard of Wood's before but I relied on my well-established theory that Costco always do their homework and only stock quality and reliable goods.

It hasn't been plugged in yet as it needs a few hours upright for the oil to settle (4hrs they claim) But it's a Swedish company, which is reassuring, and sounds economical - 178 watts I think?