Solutions to damp

[polygonum]

Quite right about it being RH - and well explained.

[polygonum]

Quite right about it being RH - and well explained.

[Chris Hogg]

I don't quarrel with the figures you chose for interior temp and humidity, but outside humidity is seldom lower than 80% and now, in the autumn, 'season of mists etc', is in the range 90 - 100% most of the time. Outside humidity only gets down to around 50%, if that, on really hot balmy summer days. Open the window and damp air comes in.

[Terry Fields]

Perhaps I should have developed this further...

If the outside is 16degC/75 percent RH, and it's 20 degC/60 percent RH in the house, the incoming fresh air will hold 12 g/cu m of water vapour and the outgoing air will hold 12g/cu m, so there will be no benefit - and a heat loss. This is where a dehumifier will help, as it will slightly heat the house and remove litres of water vapour a day (which opening the windows would not do in this case).

[polygonum]

Don't know which river you live next to - currently 39% at the back of the house and 46% at the front - and 44% indoors.

[Terry Fields]

I've just remembered an article I read in New Scientist some 30 - 40 years ago, concerning the deterioration of empty (stately) houses. It looked at all the causes, and came to the conclusion that humidity cycling was the worst offender.

I can't recall exactly, but below something like 45 - 50 percent RH wood shrunk causing paint and varnish to crack and peel, and above 60 percent spores in the wood became active.

The article concluded that the simplest way of limiting humidity cycling was to keep the property 10 degC above the outside temperature.

I suspect sweetheart's home in in the >60 percent category, which could be causing her chest problems from the spores.

[<me9]

My weather station also quotes dew point, a much more useful figure when deciding to swap air.

[<me9]

Not true usually. If temperature is taken into account an outside humidity of

100% at 5C will be equivalent to somewhere in the vicinity of 50% at 20C.

The air coming in at 5C heated to 20 will usually be a lot dryer than stagnant internal air.

Currently here external dew point is about 9C and internal 12-14C. so external air contains less H2O.

[Chris Hogg]

It's called The English Channel. I live in Cornwall, as does Sweetheart IIRC. Sea on both N and S coasts make it a damp county. My %RH info comes from a Davis weather station, with sensors outside and in. Mould tends to grow on walls behind wardrobes or in out-of-the-way corners, anywhere where air circulation is poor, even in a centrally heated house.

[stuart noble]

I imagine fire regs and security are reducing natural ventilation in multiple occupancy buildings

[The Other Mike]

Or, to put it another way, a 40mm diameter hole :)

[The Other Mike]

Locate a rolling pin or other suitable object, build a patio, store OH under patio, turn up heating, turn on dehumidifier, open a few windows. Problem solved, permanently.

[dennis]

I think you are a radius out. Then you have to take into account the mesh.

[Terry Fields]

That's all very well if the incoming air holds less water vapour than that in the house, as I calculated elsewhere in this thread. I can well imagine that in places like Cornwall, this isn't true for significant amounts of time and thus adds to the problem rather than alleviating it.

The fixed ventilation can also cause cold spots with consequent condensation and mould.

The temperature and humidity here is 13.8C/90 on the patio, 18.5C/65 at the front, and 20.0C/58 indoors. So, opening a window at the back would let in air holding more water-vapour that that in the house, but opening a window at the front would be the reverse.

[John Williamson]

To use real units, a 5 inch diameter hole with a bit of fine mesh should do it. Or four 2 inch diameter ones.

[Terry Fields]

Run it and show him how much water it collects - you might get litres a day, then offer to pour it on his side of the bed. If he doesn't like that, tell him you don't like breathing air full of mould spores as it makes you ill and can have long-term health implications.

[Chris Hogg]

Compared with gloriously sunny Cornwall at 12.30hrs, outdoors

17.7C/81%RH, indoors 22.4C/59%RH

[Terry Fields]

LOL

Opening the widow for fresh air would let in more water-vapour then already exists in th house!

[The Natural Philosopher]

well, yes and no.

Since inside is warmer, the RH of the incoming air would reduce as it warmed.

My guess is the total water content inside and out is the same.

Maybe a little higher inside due to evaporation sweat and breathing.

[Steve]

In what context, drying washing or power consumption over time? Is it cheaper to dry a load of washing over 24 hours with a dehumdifier or in a tumble dry over 2-3 hours?