Dehumidifier Struggling to get Below 50% RH

WestonDave

The problem with humidity is that it varies with temperature. You can remove water from the air in a room until it shows say 50% humidity, but if you let that room drop in temperature from 25C to 20C, that alone will push the relative humidity back up to 70%.

This is why ventilation is important. You might look outside and see its raining on a winter day and think that the air is near 100% so you don't want that air in the house. But if you bring that 100% air in at 5C and heat it up to 20C, it will drop to around 35% humidity - far better than the existing 60% humidity air you already have in your room.

This then is the tricky trade off - reducing humidity requires energy - either by running a dehumidifier with increasingly lower returns as it struggles beyond a certain point, or by dumping the dehumidifier and once a week (at least) thoroughly ventilating the house and running the heating to get it back up to level. Obviously if you can choose a warmish dry day then you may use less energy to get the same result as if you pick a really cold wet day! Getting hold of an outdoor humidity meter might well help you pick your moment.

The other issue is not creating moisture in the first place - obviously you have to breathe, but if you can avoid drying washing in the house (unless in a drier), and ensure you get as much moisture from cooking and showering/bathing outside then you will have less of a problem to solve. If that means leaving the bathroom window open with the door shut because you don't have an extractor or cooking with the kitchen window slightly open then so be it.

Mortankas

Thanks all for the input, apologies I did place a typo when stating the size of the bedroom, 14.5m2 is the correct internal area.

I live in a ground floor apartment for info

yangptangkipperbang

Jaynne wrote: »

Stick to something you know about.

Perhaps you should stick to something you DON'T know about - like a sense of humour.........................

nickj_2

an alternative to dehumidifiers is something l;like this

http://www.condensationshop.com/products/posiMaster/posimaster_roof/

ed110220

Mortankas wrote: »

Hello everyone,

I realise there is an awful lot of existing topics on dehumidifiers, and I've trawled through many posts to find an answer to my question but I cannot!

I recently bought a dehumidifier as we noticed mould starting to grow in one of our bedrooms. Many websites claim that you need to reduce relative humidity <50% to stop mould growth, ideally down to 30% in the winter season.

I bought a Duracraft DD-TEC10 dehumidifier, £150 worth of kit, awesome reviews across the board - and it really struggles to get the RH below 50, hovering around 53-55 at best when the room is fairly warm (radiator on).

The bedroom is 45m2 at the very most, not a huge size and I can't understand why the device cannot get RH below 50? I always close the bedroom door and windows before switching the device on.

Any ideas folks?

Many thanks for the time taken to read this.

Regards,

Simon.

I think the advice of less than 50% relative humidity is too simplistic because by definition relative humidity depends on temperature.

Air holds more water vapour when warm than when cold, which is of course why condensation can form when air cools.

For example if you have air at 25C and 50% RH and cool it to about 15C then you'll reach the dew point and condensation will form, which is a problem. Conversely, take 15C air at 100% RH and heat it to 25C and the RH will be reduced to about 50%.

southcoastrgi

just checked my RH & it's 37% with an outside temp of 13.1 & an internal temp of 22.4 & it's raining & my single glazed windows leak like a sleive with no insulation in the walls so i guess thats a +1 on ventalation