dehumidifier - what uses less energy running on high or low?

lstar337

All good info, though I don't agree with all of it.

Unless houses have heat recovery ventilation systems, then ventilating will cause heat to escape from a well insulated house. That heat then has to be restored via whatever heating method the house uses. If you use a dehumidifier (desiccant type), not only will you not be losing any heat, but it will add heat through the process of removing moisture from the air and reduce the load on the usual heating method.

While the heat from the dehumidifier will not be huge, or cheap, it does mean the dehumidifier is doing two jobs at once. While ventilating via windows only wastes heat that the insulation in your house is desperately trying to keep in.

CashStrapped

I disagree istar337. Heat recovery systems aside, the houses we are talking about are not energy efficient enough to worry about the small amount of heatloss from ventillation. This is the exact kind of confustion between insulation, heat loss and ventilation I am talking about. As you insulate, you replace the uncontrolled ventilation (draughts), with controlled ventillation, which targets specific high moisture producing areas of the house.

The fact that condensation is forming through the cooling of air demonstrates that the houses in question are loosing a lot of heat
anyway through the material structure of the house. Condensation is only forming because the saturated air has cooled and then condensated on a cold surface.

In the scenario you are talking about, the house would have to be either a house highly retrofitted to the point where it was nearly airtight and suffered very little heat loss. Or a modern house built to the required standard.

It is far more effective to remove excess water vapour from the source i.e when it is created (steam from shower/bath etc.) to solve the condensation issue.

You are basically using a huge amount of energy to condensate water in a specific place, rather than removing it when it was created.

As a side note, if you are worried by the small amount of heat loss from mechanical ventilation, you can get actually a self contained mvhr extractor, just for the bathroom.

In addition, the cost of the electricity, inefficiently producing heat as a side product, is far more wasteful. That money could then be put back into heating the house for longer etc.

PollySouthend

Thanks for all the info cash strapped but not sure it applies in my case.

My house is a bungalow with a suspended floor and no carpets so its certainly draughty enough! I don't use any central heating as in the winter half of the house is heated by then sun and the wood burner so the only cold room is my bedroom where I have a plug in oil filled for an hour or so at night.

When its 80% humidity outside I don't know how opening the windows will make it less humid inside?

I tend to open the windows when I first get up for an hour, close thrm and then in the winter leave the dehumidifier to work. Always open the bathroom and kitchen windows when making steam until its mostly escaped.

Why is using a dehumidifier expensive to heat? Surely all heat from electric costs the same? It just adds a few degrees in the winter

savemoney

Well I tried to get my solid walls insulated with the green deal paid £150 only to be told its now closed. I had all sorts of issues with getting people out as they only seem interested in houses close to cities or very large towns wont come out to seaside. Its very difficult to avoid condensation without having lots of insulation or have drafts understandably few of us want drafts. Even if your careful of showering and cooking, drying you can still get some especially on windows and cold areas like outside walls. Few of us can afford to retro fit old houses, again I been there tried that and got stung with grant system that suddenly closed well before it should have.

PollySouthend

Just read the Bolton guide, looks like the only thing I'm doing wrong is not heating the house enough. It regularly falls to 16 degrees, is that bad?

lstar337

CashStrapped wrote: »

In the scenario you are talking about, the house would have to be either a house highly retrofitted to the point where it was nearly airtight and suffered very little heat loss. Or a modern house built to the required standard.

Our house was built this year, and is rated A on the EPC.

It is air tight, but we have vents on the windows which can be open or closed. When open I can feel the heat escaping, when closed I cant. If I leave them closed though I will get condensation on the glass. We also have to dry some clothes indoors when the weather is wet, these are clothes that are not suitable for the tumble drier. This is when I use the dehumidifier, not often, just on occasion. Damp is not an issue for us.

When it was an issue was in our old accommodation which was hard to heat (electrical storage heating), and you really had to hold on to that heat as there was no way of getting it back once it was gone! We used the dehumidifier often in that place.

CashStrapped wrote: »

In addition, the cost of the electricity, inefficiently producing heat as a side product, is far more wasteful.

I don't see it as wasted when it is heating the house. True that electrically produced heat costs more than the gas heating it offsets, but then it is serving a dual purpose.

savemoney

The more warmer the room is the more it can hold water. as you go to bed and heating off that moisture then condenses on to cold surfaces like windows and outside walls

PollySouthend wrote: »

Just read the Bolton guide, looks like the only thing I'm doing wrong is not heating the house enough. It regularly falls to 16 degrees, is that bad?

CashStrapped

Yes, I was just typing, this issue may be that you are letting the house, or areas of the house cool too much.

If you have one very warm area and one cool unheated area, as the warm air moves into this cooler area, all the water vapour and moisture in it will turn back to water and condensate.

PlymouthMaid

I too have an old damp South West house and have to run a dehum regularly in the winter to prevent mould from growing. I ventilate loads and the house is draughty anyway but I cannot afford to heat the house that well so it is often below 15C in the winter and I have to dry washing indoors too. I know I do have some problems with one wall but can't afford to fix it but even so it would still be a damp house in the other areas.

Cardew

CashStrapped wrote: »

In addition, the cost of the electricity, inefficiently producing heat as a side product, is far more wasteful. That money could then be put back into heating the house for longer etc.

I agree with the thrust of your post, but not clear what you mean by the statement above.


The OP doesn't have central heating. So bearing in mind some bloke called Einstein stated that energy cannot be destroyed, why is a dehumidifier 'inefficiently producing heat as a side product'?

Whilst production of excess moisture is obviously important, we can't eliminate it altogether as we still have to breath!


There can be no doubt that, with modern well insulated houses, ventilation will cause heat loss as Istar337 states. If I open the trickle vents on my windows I can feel the warm air escaping outside. So obviously there has to be a compromise between heat loss and ventilation.


Indeed the link you posted includes use of a dehumidifier.