Dehumidifier advice

I am seeking some assistance in selecting a suitable dehumidifier. This will be my first such purchase and I'm getting a little lost!!

I have recently purchased a house which I will not move into until building work has been completed - which may take until August next year. My surveyor has found signs of damp in the house, which we shall be remedying - but possibly not starting work until April. The house has accomodation over 3 floors with damp affecting downstairs and one room of the first floor.

The damp downstairs is not particularly noticeable, but on the 1st floor wallpaper is coming off and plaster flaking.

I have a number of concerns in selecting a dehumidifier:

  1. The house is unoccupied and I would like the dehumidifier to run unattended, draining into a sink which may not be in the same room as the unit. What sort of pump (if any) is fitted to the continuous drain option on something like the Ebac
6200 ?

  1. The central heating is not currently operating. I see defrost options on some units ? Once the house is sorted I will reuse the unit in an unheated double garage.

  2. How realistic are the performance numbers quoted/ability to dehumidify large areas ? I'm trying to compare the Ebac 6200 with a Mitsubishi MJE16VX-E1

Thanks for any assistance you can provide

Craig

Reply to
CraigB
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Don't bother. It will not extract any significant water at low temperatures, even with a defrost unit. There is little water in the air when the house is cold.

Can you possibly get the central heating working? Having it on at a low level - say 15C, will help significantly to dry out the house by itself.

Reply to
Ian Stirling

Yes don't bother. Leave some windows open a bit and open internal doors. It'll be dry by August.

cheers Jacob

Reply to
normanwisdom

I'll go against the other two posts, lol.

I've been working on my house far too long now. I've had my dehumidifer on since the day I got metered electric.

I also have an oil filled radiator, well two at the minute due to plastering etc.

It will work just fine either on it's own or with the aid of a heater. All I wanted was to keep the house reasonable and keep some of the damp off.

Can you not visit the property once a week to empty it as it won't work at it's best in one place. I moved mine around each room giving it time to take some of the damp away. Stuff in the house (work clothes) are damp if you leave them but the house as a whole won't be as bad as if you just left it.

Mark S.

Reply to
Mark S.

You can get drain kits for some models.

We bought the largest one form B&Q about three years ago - it failed so got another (B&Q swapped it) which failed about 18 months later. Old Ebac still working but had to go back under warranty for repair too. Dehumidifiers are not very reliable in my experience.

Reply to
hzatph

I'd broadly agree with that, for the OP as stated.

That's the crucial thing with refrigeration dehumidifiers. None of them will work when cold (and the electrical consumption can be steep then too), even a hired builder's machine.

In a USA winter maybe, but a UK winter has plenty of moisture around. We'll be at 80% RH for much of it and that's still an appreciable absolute humidity

Fix whatever is putting moisture into the house, and allow as much ventilation as possible. Visit it when the weather changes and either open vents or close them. Make the most of what little warmth you can get hold of. Don't think about electric dehumidifiers in a typical unheated building until the end of March.

Reply to
Andy Dingley

As others have stated, don't bother, open each upstairs window an inch and screw the stays down if they are wooden frames, leave a gap in any curtains to allow air to flow freely between rooms, if you intend replacing fires etc, take them out now and use the chimneys as ventilation too. open any hit and miss vents that are there and unblock any that are boarded over or blocked in any way, ven ifthey are only between rooms or in cupboards - you want as much airflow as you can get - a well ventilated building is a dry building, regardless of temperature, and providing you've fixed whatever it was/is that was causing the damp in the first place...winter is actually better for drying buildings out in this way because the cold draws the moisture out of the building.

Reply to
Phil L

There is an appreciable relative humidity, and a fair absolute humidity, but you can't efficiently extract it, which was more what I was going for.

Reply to
Ian Stirling

Except on days like today when its as foggy as it comes.

The £70 dehumidifier in Sainsburys works quite well but the permanent drain is gravity only, no pump.

Reply to
dennis

Hi,

For best performance at low temperature look for one with 'hot gas defrost'.

Bear in mind when it's cold the damp will evaporate more slowly from the walls, as the air can absorb less and less humidity the colder it gets.

Units are usually specced at 30C and 80% humidity, so in a cold house they will collect a lot lot less.

The continious drain facility is usually a cap on the back which can be removed and a hose fitted.

cheers, Pete.

Reply to
Pete C

CraigB presented the following explanation :

They do not perform very well in a cold/cool atmosphere. They work best drawing in warm moisture laden air, presenting the airflow with a cold surface upon which the moisture can condense. If the air drawn in is already cold, they do not work so well. Walk into a warm room, from a cold outdoors wearing glasses and they steam up, the same effect as a dehumidifier.

Providing some heating should be your first step.

Reply to
Harry Bloomfield

As everyone says, this is not the best first step, unless the damp is very bad and there is immediate risk of rotting.

Refrigeration type dehumidifiers are specced at 30C, and at below 10C theyre not worth running. (I have tried.)

Re the damp patch upstairs I'd look at rainwater goods and pointing, and see if you've got render or some other coating on the exterior, which tends to make things worse.

Re damp downstairs, we havent yet heard any real evidence tht there is a problem to begin with. A surveyor diagnosing damp doesnt mean squiddly these days. So I'd start by telling us what symptoms of damp you have, and meanwhile do the basics like checking rainwater goods, ensuring exterior soil is below the floor level and so on.

Finally standing empty and unheated does tend to make houses damp. Once warmed up they usually dry out again.

As far as dehumids go, continuous drain models dont normally have any condensate pump, a humidistat is an important feature, and for use below 10C you need a desiccant wheel type, not the cheaper more common refrigeration type.

NT

Reply to
meow2222

Efficiency is falling because ambient is approaching 0=B0C and the refrigerator stops usefully chilling the air, not because there's any "shortage" of moisture to be had. Storing dry paper or steel tools in these conditions certainly attracts it! It's still extractable chemically, if you have a volume small enough to address with calcium chloride pots.

Over in rec.woodworking, it's an article of faith that winters are bone dry. But then they're 'merkins (and not Florida 'merkins, it seems).

Reply to
Andy Dingley

They work fine as long as the house is well insulated and draft proof. The refrigeration dehumidifiers actually raise the tempreture and they function as low output fan heaters.

The best way in the winter is to remove as much heat loss as possible, use a heater and a dehumidifier. Ventelation just wastes what heat you have.

Reply to
dennis

No they don't (to any useful level) -- do the maths.

Reply to
Andy Dingley

Well, mine pumps out 400W, subject to its operating duty cycle. This is excellent for heating and drying an airing cupboard (which has no hot plumbing in it). The heating effect would just notice in a room too, but not in a whole house.

I would add another no vote to the dehumidifier idea though. I did use one in an old house which was empty for a while, and it caused some damage. After a few weeks, I noticed it was drying out all the timber on the side facing the room in which it operated. This caused the floorboards curl up as the top dried and shrunk relative to the bottom, and the floorboards in the room above to curl down for the same reason the other way around. It took a year for them to flatten out after I switched it off. And yes, it was on a humidistat control too, but that doesn't stop significant differences in humidity between one room and other (and all the doors were left wide open). A small amount of heating and some ventilation works very well, particularly in winter when the cold outside air can't hold much water even when humidity is high. Heating that air from outside significantly reduces its relative humidity, and makes it capable of drying out a house very effectively.

Reply to
Andrew Gabriel

Any heat is useful if you are well insulated. Do the physics.. I'll help if you like..

Any water that evaporates within the building requires X kJ of energy. The dehumidifier extracts X kJ of energy when it condenses said water. They are heat pumps so are probably 50% efficient so you get another X/2 kJ of heat from the electricity used. So you get 1.5X kJ of useful heat from the dehumidifier.

If you heat and ventilate then it takes X kJ of energy to evaporate the water and you then let it out into the world. I.e. you retain zero heat.

As for the maths.. my very little one chucks out about 200W, some of the bigger ones chuck out more. This is not useful?

BTW you only need to keep the rh below about 60% to stop rust on steel.

Reply to
dennis

It's not a question of how much they pump out, it's how much they cost doing it.

Maybe it's 40W, maybe it's 400W - doesn't matter. If we re-state the problem as "Electrically heat an empty house until it's warm enough to use a refrigeration dehumidifier" then you can do it just as easily, and just as efficiently, by putting a fan heater with a thermostat in there too. kWh are heat and they cost exactly the same whether you buy them through a fridge or through a heater.

Now are you prepared to pay the cost of electrically heating an empty house to a usable temperature? That's the crucial question - how much, not how.

Reply to
Andy Dingley

This is one of the reasons a humidistat is needed. Yours will have been set to too low an RH. Drying needs to occur slowly to avoid this problem with woodwork. Zones with concrete floors and no woodwork can be dried out rapidly.

Works well when the house is occupied. Pricey for an empty house though.

NT

Reply to
meow2222

Read what I posted again. They don't cost the same as a heater. They are more efficent than using a heat pump with a ground heat source at drying out a house. The real question is how well does the house hold the heat? It can hold the heat a lot better if you are using a dehumidifier as no ventelation is needed. Any other method requires lots of ventilation which costs money.

How much does it cost to heat and ventilate a house so it dries out?

Reply to
dennis

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