How do DEhumidifiers help save on energy bills?

Brie

Can someone explain this one to me please?

I saw an article earlier today when good ol' Martin was being quoted that having a dehumidifier would cut your heating bills.  Or maybe it was just your electricity bill.  I get that having a drier house means you don't need as much heat available to allow you to dry clothing etc but is that all there is to it?

EssexHebridean

You mean a dehumidifier I think?

They produce a small amount of heat while running - in a small room this can make quite a temperature difference.
They can be used to dry washing indoors - which might mean people use a tumble drier less.

Scot_39

Think you mean Dehumidifier.

A humidifier adds moisture to air - a dehumidifier removes it.

Take Laundry airing

Basically these are cheaper to run for a few hours at a given rate than say a conventional tumble dryer -  as they use less energy / kWh.

And take the dampness out of the air without having to open windows and let cold air circulate instead to dry out the moisture it puts into air.
And saves the often even more significant added cost of reheating spaces afterwards if do open windows etc to air to remove.  To get a through flow/draft - I would be cooling 2 rooms, halls and stairway.  Over half of house.

And reduce the time need to air house for other sources of humidity - cooking, shower, even with vent fans, my vent fan struggles after baths especially,  even breathing etc.

I can get 1/2 pint to a 1pint out of air after a few bath towels or heavy cotton sheets wash etc.  And I have a 1600rpm spin washer dryer. Lower spin speeds leave more moisture in clothes as a general rule.

If you get moderate to heavy condensation on Windows or worse in some respects walls - chances are a dehumidifier will help not only reduce it, but also the risk of dampness.  As most say need 14-15C min temp to avoid mould etc.

Others say they use theirs in bedrooms to cuts down on humidity so can sleep more comfortably.  Others say just sleep with a window open - not so easy if asthmatic etc in depth of winter.

Dry air said to reduces level of dust mites, so a potential health benefit.. 

And then for many, damp air just feels colder, so need a higher heat setting.  And every deg C counts.

But then need to factor in costs to buy - my cheaper basic 10l model was £150.  And although not light, has handle so portable to move around. But would maybe need a bigger model to do larger rooms or house etc as quickly - these can run to easily over twice that.

Costs to run - uses 0.6-0.7kWh over 2-3 hours.

I won't be spending an extra £200 on a washer dryer next time.

Shedman

I thought I read somewhere that the theory is that drier air takes less energy to heat than moist air (or if not the air then the fabric of the building).   Not sure if thats scientifically proven though.  However, I do notice that when its a bit warmer outside (as it has been the last few days) but damper/more overcast the house seems slightly chillier at the same temps than it did when it was that cold but drier spell..but it wouldn't surprise me if its just a psychological effect (brighter makes you feel better than grey and dismal)

MattMattMattUK

Shedman said:

I thought I read somewhere that the theory is that drier air takes less energy to heat than moist air (or if not the air then the fabric of the building).   Not sure if thats scientifically proven though.  However, I do notice that when its a bit warmer outside (as it has been the last few days) but damper/more overcast the house seems slightly chillier at the same temps than it did when it was that cold but drier spell..but it wouldn't surprise me if its just a psychological effect (brighter makes you feel better than grey and dismal)

It is scientifically proven, but the impact is negligible. 1kg of air is 1 cubic meter, 100% humidity is 10g of water at 10c, about 17g at 20c and about 30g at 30c. The tiny amount of water works out as unimportant when you account for the mass of the air.

Eldi_Dos

@Brie, 
 If you get two tea towels, one dry and one damp sit down and have a cuppa with one towel on each knee.After about ten to fifteen minutes check the temperature and comfort of your knees.
This will show the benefit of living in a dry atmosphere.

Effician

No need for a dehumidifier to dry the indoor air at this time of year , plenty of relatively dry air on tap from outside if you know how to use it.

Having done the no dehumidifier , had dehumidifier & then sold dehumidifier routine,  for us it's far cheaper to purchase & run circulating fans which circulates warm air & keeps condensation lower than with a dehumidifier. Only a room sealed log burner for heating here so not really a typical scenario ,ymmv.

_Sam_

Effician said:

No need for a dehumidifier to dry the indoor air at this time of year , plenty of relatively dry air on tap from outside if you know how to use it.

Hmmm 88-89% humidity outside, wouldn't call it a dry air on tap! https://www.metoffice.gov.uk/weather/forecast/gcpk9yegm#?date=2023-01-28

We bought dehumidifier specifically to save money on heating. Dry air feels warmer so less heating needed, dehumidifier produces a bit of heat in addition to ridding the air of moisture, no condensation on windows now, no worry about mould forming where we can't see it (behind wardrobes etc), plus they say dryer air is healthier than moist air.

We keep the humidity at around 40-50%, prior to dehumidifier it was 70+% all the time, with lots of moisture on the windows and mould forming there.

Effician

_Sam_ said:

Effician said:

No need for a dehumidifier to dry the indoor air at this time of year , plenty of relatively dry air on tap from outside if you know how to use it.

Hmmm 88-89% humidity outside, wouldn't call it a dry air on tap! https://www.metoffice.gov.uk/weather/forecast/gcpk9yegm#?date=2023-01-28

You don't seem to have grasped the meaning of relative humidity.

_Sam_

Effician said:

_Sam_ said:

Effician said:

No need for a dehumidifier to dry the indoor air at this time of year , plenty of relatively dry air on tap from outside if you know how to use it.

Hmmm 88-89% humidity outside, wouldn't call it a dry air on tap! https://www.metoffice.gov.uk/weather/forecast/gcpk9yegm#?date=2023-01-28

You don't seem to have grasped the meaning of relative humidity.

I have by now! We had a good discussion on it in the other thread.

Moisture which is present in the air doesn't disappear when you raise the temperature of the air. When you let the outside air in, you let in the exact amount of moisture that was outside, measured in grams per cubic meter of air. 

Raising the temperature of that moist air only means that the same cubic meter can now accept more moisture, hence your relative humidity reading. But the actual water you let in via the "outside tap" stays the same.

masonic

_Sam_ said:

Effician said:

_Sam_ said:

Effician said:

No need for a dehumidifier to dry the indoor air at this time of year , plenty of relatively dry air on tap from outside if you know how to use it.

Hmmm 88-89% humidity outside, wouldn't call it a dry air on tap! https://www.metoffice.gov.uk/weather/forecast/gcpk9yegm#?date=2023-01-28

You don't seem to have grasped the meaning of relative humidity.

I have by now! We had a good discussion on it in the other thread.

Moisture which is present in the air doesn't disappear when you raise the temperature of the air. When you let the outside air in, you let in the exact amount of moisture that was outside, measured in grams per cubic meter of air. 

Raising the temperature of that moist air only means that the same cubic meter can now accept more moisture, hence your relative humidity reading. But the actual water you let in via the "outside tap" stays the same.

At 0C, 88% humidity air contains 4.3 g/m3 water. Bring in that air from outside and heat it even to 15C and the humidity is 33%. This is very dry compared with the typical indoor humidity of 60%+. The ideal moisture content of indoor air will be around 6-8 g/m3, assuming your home is heated to a reasonable temperature. Replacing air with 8-15 g/m3 moisture with that of 4-6 g/m3 will have a dehumidifying effect.

Personally, what drives my decision to use a dehumidifier vs an 'air change' (opening windows on opposite sides of the house to get a brief through-flow), is pollution levels outside. The cost of heating up the cold air vs keeping the house warm and dry using the dehumidifier is probably quite negligible, just like the cost of heating dry vs moist air.