Dehumidifier

[MuddyMike]

I am looking to buy a domestic dehumidifier, any recommendations?

Mike

[Tim Watts]

What do you want it for? Room area, expected operation times (ie all the time vs occasionally), doesquiet vs noisy matter?

[David in Normandy]

Avoid the no-brand ones from Argos, they are cheap nasty Chinese construction. Mine was very noisy and failed after three months (fan gave up). I've since got it jerry rigged with an office fan blowing through it! Still noisy though (pump chugs loudly).

I've also got a Delonghi which was expensive when bought ten years ago but it is still running today 24 hours per day! A case of you get what you pay for.

[Andrew Gabriel]

I bought 3 from Homebase in a sale about 10 years ago, reduced by 75%. They looked exactly like an EBAC model, but they are not branded. One had an early component failure on the control board, but I was fortunately able to fix that easily, and didn't even bother using the guarantee. Two of them have been moved around often between different family members (although I've been careful to observe the instruction to avoid use for 24 hours after moving). All still work very well. Can use internal tank, or external drain. Damn heavy though, which combined with bulk, makes carrying tricky.

[js.b1]

If you heat by electric-only...

- Meaco DD8L dessicant dehumidifier.

- 380W normal mode, 800W laundry mode = HIGH heating output.

- Dessicant dehumidifer uses a heater as part of their operation, this must be borne in mind.

- Perform well at low temps, which combines with the heater to maintain temps higher than a compressor unit.

- DD8L once it has reached your desired humidity setting of 50% or 60% turns off the heater AND fan, then turns back on every 30mins to sample the air to see if it needs to dehumidify. It does not leave the

30W fan running all the time like earlier dessicant dehumidifiers.

- If a powercut occurs it turns back on if it was left running (very useful on a boat or left unattended).

- Not much more they can improve - a side-&-top exit would be better re air velocity.

Note if you heat by gas 1) you may not need the extra heat provided by a dessicant dehumidifier and 2) you may not want to pay for it either compared to gas heating where temperatures are not at very low levels.

If you heat by gas...

- Mitsubishi compressor dehumidifier.

- Well built, digital & non-digital versions

- Very large water tank although a permanent drain can be used as with all of them.

- Draws about 220-320W from memory, much cheaper to run than a dessicant unit but TINY HEAT OUTPUT.

- Do not heat a room much, do create draughts in a cold room, do not perform so well at very low temps unlike dessicant units.

With all dehumidifiers there is a blast of air out of them. This will blow away the boundary layer of air on walls & ceilings and can create draughts. So they are not ideally suited near people if the temperatures are relatively low.

With all dehumidifiers if you have a very high number of Air Changes Per Hour they will run more often to dehumidify the air - this can mean running almost continuously. Something to factor in to the purchase price.

An alternative to dehumidifier is a timed extractor (runs every

4-8-12-24hrs for N minutes) and increasing heating. Warmer air will hold more moisture, extracting air will remove humidity. Again, something to factor in re comparison. If you run a typical 4-inch extractor for 10mins it takes 7mins at 650W to put back the heat extracted, that is not much re cost.

[js.b1]

Cost of running a 4" fan 3 times for 10mins a day...

- 0.5hr x 0.020kW x 11p =3D 0.11p per day (insignificant).

Cost of heating replacement 0oC air to 20oC

- 90m^3/hr for 10min =3D 15m^3 of heated air at 20oC extracted

- Assume replaced by air at 0oC (drawn through house vents)

- Heater run on minimum setting which is 650Watts

- Air SPH =3D 716J/Kg K, air density =3D 1.3kg/m^3, 1 watt =3D 1J/sec, Volume =3D 15m^3.

- 650Watts * N-seconds / 716 / 1.3 =3D 20oC rise

- N-seconds =3D 20 * 1.3 * 716 / 650 * 15 =3D 430secs =3D 7.2min.

- 7.2min x 3-times a day =3D 22 min per day

- cost =3D 0.37hrs x 0.65kW x 11p =3D 2.65p

So even if you have to extract more than 3x a day for 10mins, it is not a big cost.

True, but at 0oC air drawn in has very little moisture content. So a crude calculation, but depending on the need for dehumidification it swung it to an extractor. I use a 2kW fan heater to blast the temp back up very quickly.

A dehumidifier costs more to run, but does offer a little heat (compressor) or a lot of heat (dessicant). On balance the extractor method works well. The air RH in the room is 56-48% and most dehumidifiers stop at 50% - which is not low enough to stop condensation on single glazing.

So on balance the extractor was cheap to buy, cheap to run, and the saving went in a ****-load of insulation both Marmox & Celotex. Just got to find time to fit it! :-)

Dehumidifiers work best for open plan or one-floor flats, not so good across multiple floors and they are not silent if you have to "sleep with them". For their purchase cost, running cost & eventual replacement cost I think a proper split mount air-con might be better value for money. About =A3279-379, heat pump capability, cooling capability, plus dehumidification capability and at a lower noise than most dehumidifiers.

[ARWadsworth]

But an extractor fan can also give advantageous air changes to other rooms in the house.

[ARWadsworth]

What would the true cost be if you take into account that for 8 months of the year the reheating costs are zero as the heating is not on?

[js.b1]

No chance, unless you have a very modern house & too-low ACH.

Running 30% of the time =3D 0.2kW x 8hrs x 12p x (8/12*365)/100 =3D =A347 pa. Purchase cost =A3300 for 4x Mitsubishi EVX over 20yrs =3D =A31200. Total 20yr cost =3D =A32140.

Dessicant is probably not a whole lot different - they are =A3130 but the running costs are about double, so the saving of =A3170 on purchases is clear but I very much doubt they will last 5yrs. I suspect 4yrs.

I would also add 4 Xpelair fans could well be required over 20yrs. We will ignore the cheapest shed fans for obvious reasons :-)

Perhaps I am pessimistic on appliance life, both may last 8yrs.

Dehumidifiers can end up per-room or per floor, they do not work well through closed doors. Great for flats though.