Background: I’ve recently moved into a quite old house, part of which has some problems with condensation and damp.
Most of the house is heated and is warm and dry, except for an unheated wing containing the kitchen, and at the end of the kitchen, an unheated utility room that is very cold due to thick walls and construction somewhat like a cellar.
As warmed air from the heated part of the house flows through the unheated wing, it tends to deposit any moisture it is carrying, especially in the very cold utility room, and especially on the coldest, thickest wall there.
Heating solutions are being explored, but may be expensive and wasteful to run due to the inherent coldness of the antique structure.
Ventilation will certainly help, but will also make heating even more pricey.
Insulation cladding can be fitted on the walls - some parts of the kitchen already have it, and it effectively prevents condensation settling by isolating the cold wall from the warm humid air…
… but it occurred to me that rather than attempting to prevent condensation on that very cold wall at the end, a passive dehumidifier could be fitted, if such a thing exists.
A large sheet of stainless steel, thermally bonded to the cold wall. On the face side of the metal sheet, a herringbone arrangement of fins, channeling condensation to a central collection point for drainage away and out of the building.
Does this solution exist already? (I tried the Googles. They did nothing)
If not, is there a reason why this would be a bad idea?
I would call that more of a condenser than a dehumidifier insofar as it is only going to bring the air down to just below 100% RH at the temperature of the wall, and thus, isn’t going to pull out enough water to prevent condensation elsewhere. I think the other problem that you are going to run into is that the stainless steel will heat up as the warm moist air condenses on it and it will become ineffective unless you are somehow actively cooling it on the back side. Basically, unless this wall is much lower temperature than every other surface it is only going to have a very marginal effect on reducing condensation.
The warm air will naturally carry more moisture than when it is cooled by entering this unheated part of the house, and the only things you can really do are to heat this part of the house or actively dehumidify the air. Insulation is probably the way to go here to keep those areas heated without excess cost, or else seal off the utility room if possible.
It is colder. It’s a very thick stone wall with enormous thermal mass. Basically, the condensation effect I am describing is already a thing, just without a collection system. If there is a particularly cold spell, the wall cools even more (and of course we’re heating the house) so there is an almost guaranteed temperature gradient with the wall at the cold end.
Why not try a small scale experiment. Get a 12x12 sheet of steel with a bit of thickness to it from your local big box hardware store. It doesn’t have to be stainless, just pay attention to where it’s going to drip and how hidden the area is since it’ll rust.
Attach it to the wall. I’m picturing it being flat against the wall and then going around the top, left and right sides with something like hot glue (for easy of installation and removal) to hold it to the wall. Not the bottom so you don’t trap any (as much) moisture behind it and see how fast it collects water.
ETA, another thing you might try, if the layout of the room works for this, get a plastic sheet and put it over the wall. If you seal it well enough to the wall, air won’t be able to get behind it so the condensation should form on the front. Then it’s just a matter of funneling into something.
Certainly that’s something to consider, but I think the risk is greatest where there is standing, collected water. I’m describing something that makes water drain away
Although small kitchens in the UK are not always heated. Domestic heating in the UK typically comprises a gas boiler circulating hot water through radiators. In a small kitchen, any space that could host a radiator is probably already occupied by cabinets or appliances. Besides, the idea of heating a room that already contains things that emit heat is also somewhat weird.
This kitchen doesn’t have heating because it was like that when we moved in last month. Also, there’s nowhere really to put a radiator.
Insulating the walls will work (it’s working in the parts of the kitchen that are insulated), but the warm humid air will find any cold surface to condense on. We thought we had a leaky pipe, but it was just condensation forming on the surface of a cold feed pipe. We can lag or box in that pipe, but the condensation will find something else cold.
Additional extractor fans will probably feature in the long term solution.
I would advise caution with this - several ‘horror stories’ are circulating in the UK at the moment about homeowners who have had this installed (even by reputable firms) and then found their homes are unmortgageable, because surveyors are not happy with the product certification (or something along those lines - it’s not entirely clear what the root of the problem is).
I think one of the key issues with spray foam insulation is that it can be used to more or less hermetically seal a roof space - which seems like a great idea from the perspective of insulation and cost saving on heating, but ventilation is a necessary part of moisture control.
At the moment, there’s a lot of discussion about heating and insulation in the UK as fuel prices have risen sharply, and there is some awful advice being circulated (some of it coming from government sources); like ‘just heat one room in your house and stay in it to keep warm’ - maybe workable in an emergency - for example using standalone electric heat while awaiting a breakdown fix - but not a good strategy for any longer term, as the unheated portions of the house will condense the moisture that is being evaporated in the one heated room.
There is also a general notion that sealing up every little gap will keep the home warmer (you see it in commercials for double glazed windows) - but again, ventilation is important, and is often neglected.
Here in NZ there are lots of firms that sell Heat Recovery Ventilation (HRV) systems - a consequence of historic building practices that have resulted in many older homes having inadequate thermal control and condensation/mould issues.
The principle is that warm moist air is extracted from the house via a heat exchanger, warming cool dry air from outside the house. In this way fresh warm air is introduced and moisture removed and drained.
The sort of exchanger used in a HRV may be the sort of thing you are looking for. However, the practicalities of installing such a thing in a typical UK construction may be too difficult, even if you could find a supplier.
We certainly did not regret installing exterior-wall and ceiling insulation in our house in the UK, along with updated uPVC double-glazing. We did have a radiator in the kitchen, though. Can you fit an electric ceramic panel-heater in those spaces - although with UK energy prices, maybe not?