Is it cheaper to use a dehumidifier: 1) to heat my house? 2) to dry my clothes?
shiphen
Posts: 82 Forumite
Hello
I want to know if using a dehumidifier is a cheaper way to:
1.) HEAT MY HOUSE (and keep it dry).
2.) DRY MY CLOTHES (on a clothes air dryer rack)
1) HEATING MY HOUSE
1.1) In favour of a dehumidifier
A dehumidifier not only heats your house with the direct electrical heat energy it uses, but also because when water evaporates it cools down [think getting out of a bath] and because energy is neither created nor destroyed [due to "law of conservation of energy"] it will actually generate quite a lot more heat for unit of energy than conventional heater due to heat generated by condensation. (I've been told in total you get about x2 to x3 times the heat per unit of electrical energy that a conventional electrical bar or blow heater for example would generate)
1.2) Against a dehumidifier
1.2.1) Electrical energy is quite a lot more expensive per watt than say gas or kerosene heating oil.
1.2.2) Worse, there is a subtle problem. Which is that as well as flowing down a humidity gradient (from wetter towards drier places), water also flows down a thermal gradient (from hotter toward cooler places).
1.3) Discussion
Thinking this through, this means that when the air in a room becomes extremely dry, the moisture (i.e. water) in a wall can be 'sucked' through a wall down the humidity gradient. And when it arrives at the surface of the wall as it evaporates, it COOLS down the surface of the wall down.
This is quite hard to get your head around, but with the inside surface of a room's wall (or floor) being potentially COOLER than the outside, you can be sucking water into a room not just because the air is drier in the room, but because the inside surface of the wall is cooler than the outside surface of the wall. I am told that eventually (and very bizarrely) you can end up with a wall that is literally dripping wet even despite the fact that you have been running a dehumidifier in it for weeks. !
For this reason if a room's air becomes too dry you can "suck" water into your room, rather than driving out of your room.
On the other hand if you just ran an electrical heater you would drive the water OUT, down the thermal gradient. Simples!
So if you run the dehumidifier too hard, despite emptying buckets and buckets of water out of the dehumidifier in the long run you are making your wall wetter - and as soon as you turn the dehumidifier off the humidity gradient would come to the surface even worse. It's as if the room had become "addicted" to the dehumidifier.
My understanding is that this can be a serious problem in cellars where there is a seemingly limitless source of ground-water in the soil/rocks etc behind the wall. I am told that partly for this reason many modern dehumidifiers now contain heaters too.
2.) DRYING CLOTHES
2.1) Condensing tumble dyers (make house damp!)
If like me you dry your clothes in a condensing tumble dryer you will soon discover that because they are not terribly efficient, the exit air to your tumble dryer is actually very heavy with water vapour. And for this reason condensing tumble dryers can directly make your house damp. For this reason I have now bought a dehumidifier.
2.2) Central heating or dehumidifier?
Due to the arguments presented above it's not completely clear to me whether it would be best to get rid off the unwanted water vapour ("dampness") that it generates by running the dehumidifier or whether it would be better to simply turning up my gas central heating!
If doing the latter, obviously you need to have a little bit of fresh air into the building to help the vapour escape. (REMEMBER: Hot air holds more water than cold air, and by heating the air in your house you are encouraging water to evaporate off your fabrics/walls etc into the air. You then need to expel this air - e.g. through a slightly open window.)
OR should I just run a dehumidifier (not too hard, not too long) but keep the windows firmly closed?
CONCLUSION?
All extremely confusing and much more complex than you might have thought!
J
I want to know if using a dehumidifier is a cheaper way to:
1.) HEAT MY HOUSE (and keep it dry).
2.) DRY MY CLOTHES (on a clothes air dryer rack)
1) HEATING MY HOUSE
1.1) In favour of a dehumidifier
A dehumidifier not only heats your house with the direct electrical heat energy it uses, but also because when water evaporates it cools down [think getting out of a bath] and because energy is neither created nor destroyed [due to "law of conservation of energy"] it will actually generate quite a lot more heat for unit of energy than conventional heater due to heat generated by condensation. (I've been told in total you get about x2 to x3 times the heat per unit of electrical energy that a conventional electrical bar or blow heater for example would generate)
1.2) Against a dehumidifier
1.2.1) Electrical energy is quite a lot more expensive per watt than say gas or kerosene heating oil.
1.2.2) Worse, there is a subtle problem. Which is that as well as flowing down a humidity gradient (from wetter towards drier places), water also flows down a thermal gradient (from hotter toward cooler places).
1.3) Discussion
Thinking this through, this means that when the air in a room becomes extremely dry, the moisture (i.e. water) in a wall can be 'sucked' through a wall down the humidity gradient. And when it arrives at the surface of the wall as it evaporates, it COOLS down the surface of the wall down.
This is quite hard to get your head around, but with the inside surface of a room's wall (or floor) being potentially COOLER than the outside, you can be sucking water into a room not just because the air is drier in the room, but because the inside surface of the wall is cooler than the outside surface of the wall. I am told that eventually (and very bizarrely) you can end up with a wall that is literally dripping wet even despite the fact that you have been running a dehumidifier in it for weeks. !
For this reason if a room's air becomes too dry you can "suck" water into your room, rather than driving out of your room.
On the other hand if you just ran an electrical heater you would drive the water OUT, down the thermal gradient. Simples!
So if you run the dehumidifier too hard, despite emptying buckets and buckets of water out of the dehumidifier in the long run you are making your wall wetter - and as soon as you turn the dehumidifier off the humidity gradient would come to the surface even worse. It's as if the room had become "addicted" to the dehumidifier.
My understanding is that this can be a serious problem in cellars where there is a seemingly limitless source of ground-water in the soil/rocks etc behind the wall. I am told that partly for this reason many modern dehumidifiers now contain heaters too.
2.) DRYING CLOTHES
2.1) Condensing tumble dyers (make house damp!)
If like me you dry your clothes in a condensing tumble dryer you will soon discover that because they are not terribly efficient, the exit air to your tumble dryer is actually very heavy with water vapour. And for this reason condensing tumble dryers can directly make your house damp. For this reason I have now bought a dehumidifier.
2.2) Central heating or dehumidifier?
Due to the arguments presented above it's not completely clear to me whether it would be best to get rid off the unwanted water vapour ("dampness") that it generates by running the dehumidifier or whether it would be better to simply turning up my gas central heating!
If doing the latter, obviously you need to have a little bit of fresh air into the building to help the vapour escape. (REMEMBER: Hot air holds more water than cold air, and by heating the air in your house you are encouraging water to evaporate off your fabrics/walls etc into the air. You then need to expel this air - e.g. through a slightly open window.)
OR should I just run a dehumidifier (not too hard, not too long) but keep the windows firmly closed?
CONCLUSION?
All extremely confusing and much more complex than you might have thought!
J
0
Comments
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Phew! Overthinking things a little maybe.0
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PS. The average user of a tumble dryer spends £60 to £100+ on electricity running it. We are here to discuss ways of saving money, no?0
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Do all dehumidifiers heat the air anyway? I'm not sure that compressor ones do. Desiccant ones do, but that's because it's necessary to renew the desiccant material, and they only use enough heat to achieve that goal. I don't think they put out enough heat to be considered a useful means of heating a building. So I'd go with using the dehumidifier to reduce humidity and the central heating to heat.Let's settle this like gentlemen: armed with heavy sticks
On a rotating plate, with spikes like Flash Gordon
And you're Peter Duncan; I gave you fair warning0 -
Do all dehumidifiers heat the air anyway? I'm not sure that compressor ones do. Desiccant ones do, but that's because it's necessary to renew the desiccant material, and they only use enough heat to achieve that goal. I don't think they put out enough heat to be considered a useful means of heating a building. So I'd go with using the dehumidifier to reduce humidity and the central heating to heat.
mine does. The hallway was the coldest part of the house, but goes from 18degC to 21degC using the dehumidifier - you can feel the vented air is much warmer than ambient.
i don;t even want to think what my next electric bill will be...0 -
Quote:
'mine does. The hallway was the coldest part of the house, but goes from 18degC to 21degC using the dehumidifier - you can feel the vented air is much warmer than ambient.'
The amount of heat needed to raise one room's temperature by three degrees would, surely, not be enough to keep a room heated to an acceptable temperature without another heat source and, also, using dehumidifiers to heat a whole house would require several machines.
We once had an aircon/dehumidifier and found it quite noisy, too.0 -
Yes I wasn't planning to use the dehumidifier alone to heat my house in winter. And yes the big down-side is that even the quieter ones are somewhat noisy. My main question is am I actually wasting my money heating my house to the extent to which it would be happening by using a dehumidifier more than I have to?0
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I personally own a Meaco dehumidifier which features a Laundry Mode. In Laundry Mode the dehumidifier runs at full power until it is stopped (by operator or full water tank etc).
In Laundry Mode the Meaco can increase the surrounding air temperature by 12c degrees which is fairly warm. If using the Meaco in LM in a single room then I'd dare say that you could get away without turning on the heating for that room.
I actually run a dehumidifier review website and have some neat comparisons between wattage and extraction rates however I am currently writing it up as a post so I won't post the info here just yet.
Don't forget that tumble dryers also shrink clothes. I personally don't like them but each to their own.
Oh, just to add that desiccant dehumidifiers are lighter and quieter than compressor models due to lack of compressor parts. Desiccant units are also more efficient than compressor models at temperatures below 20c and can operate at lower temperatures than compressor models.
Hope that helps a little.0 -
changed_username wrote: »In Laundry Mode the Meaco can increase the surrounding air temperature by 12c degrees which is fairly warm. If using the Meaco in LM in a single room then I'd dare say that you could get away without turning on the heating for that room.
12C is an awful lot.
I run a Meaco and in a room with a thermometer and closed door it has only raised the temp by 2C.0 -
> I actually run a dehumidifier review website and have some
> neat comparisons between wattage and extraction rates
Sounds interesting - I would like to see this. Please provide link (or else please PM me with it).
MEACO20L
I saw that Meaco were extremely well reviewed by Which.co.uk as being both quiet and efficient. My sister bought a MEACO20L which has a 20 litre tank which it fills up in about 24 hours (about 4 or 5 times faster then her existing machine) - although I don't know about wattage(s) it uses in the different modes.
BROLIN BR8D
I have recently purchased a desiccant BROLIN BR8D from Dehumidifiersuk.com who talked me into it. So far I am not at all sure what I think about it. It seems to fill up moderately slowly(??). However, I have yet to do back to back comparison and I do not know what wattages it runs at in its different modes. Despite what I was told, I would say that is not exceptionally quiet. It has a Quiet mode (called Silent in the instructions) that is only fractionally quieter than it's Normal mode...
"CHANGED USERNAME" If you have wattages and extraction rates for the Brolin BR8D I'd be very interested to see them.
UK CLIMATE
I think Winter in the UK is a tough time to be trying to get clothes completely dry using an air drier. I am told that you need to get the Relative Humidity down to better than 50% in order to get your cloths properly dry. [Note that if you don't when you come within a few months they will smell distinctly musty and need washing agains!]
e.g. Here in Oxford the outside air is in December is cold (7 to 2 degreesC) [See:
http://www.holiday-weather.com/oxford/averages/ ]
...and the average Relative Humidity is about 80-85%
http://www.myforecast.com/bin/climate.m?city=61003&metric=false
And worse, on a day like today the strong wind (25+ MPH) is whistling through any gaps around doors / windows / vents etc and is flooding the house with relatively damp air.
USING A COVER TO AIR DRY
I don't want to waste energy drying the rooms in my house down to 50% RH (which is probably impossible in this weather in any case!), so using a cover with my dehumidifier would seem to be much more sensible!
However I am keen to find a cover that fits properly due to the obvious fire risk.0
This discussion has been closed.
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