really stupid Q - ventilation vs warmth

[tobydog]

Joce - thanks very much for the thermal curtain information. I will ask Mrs. T to have a look at it. We know someone who has already done some great work for us on our Roman blinds. The prices per metre are good as well. We're getting there.

 

[AMc]

My personal take is "draughts" remove heat in an uncontrolled, unplanned way.
"Ventilation" removes wet and/or smelly air and allows fresh air in in a controlled manner.

Remove wet/smelly air out by forced extraction as close to the source as possible - bathroom extractors and cooker hoods.
Plug gaps and holes that allow the wind to whistle in and out sucking away your heat.
If it loses heat on a windy day and not on a still one it's a draught and should be stopped, anything more controlled can be considered ventilation.
I'd be amazed if most of us could reach the levels of airtightness where the lack of fresh air becomes an issue in and of itself.

If you have issues with rising damp and condensation then I suspect that opening windows and turning up the heat is dealing with the symptoms not the cause - I appreciate that some of our houses are built into hills etc. and damp there is a lot harder to cure.

I wish we'd put in MHRV when we renovated, I baulked at the capital cost and disruption. Having been through almost as much disruption fitting the heating and been disappointed with the thermal efficiency in some rooms I wish I'd been braver.
I have part of my house that collects significant amounts of solar gain and other parts with north facing windows and solid walls that get none. MHRV would have allowed me to distribute heat from one place to the other for great chunks of the year when I have to heat the colder parts of the house.

 

[Roger H]

A single room MHRV costs around £200 (unfitted) so not exhorbitant. The internal arrangement is not much larger than a box file and the duct passes through the external wall like a normal vent axia. My installation will now have to wait til next year/and/or lottery win.. Anyone have a single room version in operation?

 

[worms]

A single room MHRV costs around £200 (unfitted) so not exhorbitant. The internal arrangement is not much larger than a box file and the duct passes through the external wall like a normal vent axia. My installation will now have to wait til next year/and/or lottery win.. Anyone have a single room version in operation?

Can you provide a link to the one you've seen? I am about to buy a standard humidistatic fan to mount in the loft above the ceiling in the bathroom and vent through the roof, replacing an old one that is in the (screwed shut) window. At £200 I could be swayed, but the ones I've looked at have been more than twice that. I do want to be able to have a humidistatic switch on it though.

 

[Roger H]

Ok, £271 inc vat -
http://www.dealec.co.uk/acatalog/ve...-444370.html?gclid=CP23mP_8-LICFaTKtAodMiYAuQ

One on ebay for £185.00 though and others at Vent Axia site http://www.vent-axia.com/range/lo-carbon-tempra.html

 

[tobydog]

Well, I had to concede on Saturday and we finally turned the heating on for the first time this year. Mr's T. was on the verge of reporting me to the police for physical abuse so I thought it wise to take note. I played it down by suggesting that I was about to 'test' it anyway but it worked out fine.

What I wasn't prepared for was for all of our windows turning into a mini Niagara's. I know it's been a wet year, and I've picked up some excessive results with the damp meter, but this was ridiculous. The house must have just soaked it all up during the summer as I suspected and I turned the house into a sauna when the heating came on. In hindsight I should have put the dehumidifier on at the same time, however, even with that, Sunday night was the same.

I know it's been cold but we simply don't have enough ventilation in our house. The windows fit very tight and have side opening sashes which makes it impossible to leave them cracked open for background air like we could with top openers. We've had fires in the log burner and I've used the dehumidifier several time but this had no affect. We have little air flow but thin cold walls, doors and other surfaces so not a good combination. I'm hoping this will finally calm down as the colder drier air comes along.

Out of desperation (because I know what's coming over the next month or so) I've finally invested in one of those Karcher Window Vacs. They have received some very good reports and will save me a great deal of time. We need the smaller blade for our windows and this provides even more suctions than the larger standard one. I want to catch the water when I see it and not let it evapourate back into the house. I only have weekends to do this unless I can get Mrs. T excited about the idea of using it during the week :roll: .

I'll report back with my results.

 

[worms]

Roger H, thanks for the links.

I am half-way through insulating the internal face of the external bathroom wall. For various reasons, this is getting a layer of celotex. It is interesting to note that after a shower, with the room heated and the current extractor fan running, even the foil layer of the celotex gets a film of condensation. It dries off fairly quickly, but I must admit I had never really expected it to form on the insulation at all.

 

[Flyfisher]

I'm not that surprised about the condensation.

Consider a bathroom at an ambient temperature of, say, 20C. As long as the ambient temperature has been constant for long enough then every single thing in that bathroom will also be at a temperature of 20C (assuming the walls and windows aren't losing heat too fast to the exterior). Thus, the celotex surfaces will be at the same temperature as the surfaces of porcelein fittings and any mirrors. So if steam will condense on the basin and mirror, it will also condense on the celotex because they are all the same temperature.

This seems counter-intuitive because when we touch a piece of 20C basin it will feel cold whereas a piece of 20C celotex will not - even though they are both at the same temperature. This is because the celotex is a poor conductor of heat, meaning that the heat from our fingers will not be drawn into the celotex (well, not very quickly) and so our fingers are not cooled when we touch it - so it feels 'warm'. Conversely, a porcelein basin is a much better conductor of heat so when we touch it the heat from our fingers is drawn into the basis, which cools our fingers, which gives us the 'cold' sensation.

 

[tycarregydwr]

I'm not that surprised about the condensation.

Consider a bathroom at an ambient temperature of, say, 20C. As long as the ambient temperature has been constant for long enough then every single thing in that bathroom will also be at a temperature of 20C (assuming the walls and windows aren't losing heat too fast to the exterior). Thus, the celotex surfaces will be at the same temperature as the surfaces of porcelein fittings and any mirrors. So if steam will condense on the basin and mirror, it will also condense on the celotex because they are all the same temperature.

This seems counter-intuitive because when we touch a piece of 20C basin it will feel cold whereas a piece of 20C celotex will not - even though they are both at the same temperature. This is because the celotex is a poor conductor of heat, meaning that the heat from our fingers will not be drawn into the celotex (well, not very quickly) and so our fingers are not cooled when we touch it - so it feels 'warm'. Conversely, a porcelein basin is a much better conductor of heat so when we touch it the heat from our fingers is drawn into the basis, which cools our fingers, which gives us the 'cold' sensation.

Ok, that seems to make a lot of sense. But in that case, why don't we always get this in bathrooms (or other rooms) - mirrors always mist up, but bathroom walls and ceilings don't always? Sorry if I'm bring thick about this, I am trying to understand!

 

[Flyfisher]

Misty mirrors are very visible, of course, so we're used to seeing them mist up, but I'd bet that if you ran your finger over the walls and doors then you'd also notice a thin film of condensation (assuming the bathroom was uniformly filled with steam of course).

Also, if the bathroom walls are papered, for example, the condensation may soak into the paper and thus not be quite so noticeable.

 

[worms]

Yes, it is all very logical and I guess if I had ever actually thought about the Celotex question, I would have realised that it would get the same amount of condensation as the painted/papered walls in the rest of the room (the mirror is deliberately above the radiator, so that it remains clear). It is just that I had never thought it through at all and somehow it came as a surprise!

But it also shows that simply warming the wall (or, more accurately, eliminating the coldness) is still no substitute for ensuring adequate air flow for the surfaces to dry again.

 

[88v8]

Our windows are also steaming up, I expect one could collect a few pints in the day if one were so inclined. Consdering that humidity in the house is at 70%+, I suppose that's not surprising, the single-glazed windows are the coldest element, and I'd rather the water condensed there than on or in the walls.
Nothing about this is unique to 1600s house - I recall exactly the same at my parents' 1950s house in the pre-central heating era.
Once we light the fires, it will improve.

To get background ventilation through double-hung sashes... from a 1920s book I can't currently lay hands on... make a board the width of the sash and about 1" tall, put it on top of the top sash and close the window. It won't quite close so now you have ventilation through the meet rail. If 1" tall gives too much ventilation, make it 'shorter'.
This does of course defeat the window lock, but you can reinstate security with sash stops.
http://www.lovehandles.uk.com/bramah-rola-r1-01-r1-03-r1-04-sash-stop.html?gclid=CO_D7KaQhbMCFUfKtAodOVQARg
Other less embarassing retailers, and other designs, are available.

Ivor

 

[billybuntus]

As I've already posted. Modern people living in an old house should have a dehumidifier. We run ours about 14 hours a day (from when I get up until when I go to bed. It extracts 3 litres of water each and every day.

The house is 300% more comfortable for it. This one doesn't have a humidistat so just runs until I switch it off. When I feel inclined I'll buy an equivalent size A+ energy efficient unit with a humidistat and set it around 50% RH

If you do buy one don't buy a small unit as they are a waste of time in a home and you'll be constantly emptying a tiny tank.

 

[tobydog]

I have a feeling that's what our neigbours do. We have a similar timber / thatched house and when we are saturated, they are bone dry (at least their windows are first thing in the morning). Our unit is quite effective when I'm blasting the thing out looking for 40% RH but it's very noisy. There is hardly anywhere in our cottage where you can't hear it so I tend to be selective rather than continuous. The other setting is 60% which is probably healthier. I never achieve either really. When it get's very cold and dry outside nature / science will take over and draw the moisture out.

 

[billybuntus]

I have a feeling that's what our neigbours do. We have a similar timber / thatched house and when we are saturated, they are bone dry (at least their windows are first thing in the morning). Our unit is quite effective when I'm blasting the thing out looking for 40% RH but it's very noisy. There is hardly anywhere in our cottage where you can't hear it so I tend to be selective rather than continuous. The other setting is 60% which is probably healthier. I never achieve either really. When it get's very cold and dry outside nature / science will take over and draw the moisture out.

I just think it makes perfect sense. I've tried living in a damp house and its no fun. My old and wise uncle pointed out that he's been using a dehumidifier for many many years. He's also renovated 10+ older properties and has found the only cure to modern living is a dehumidifier.

Keeping your home heated by leaving the heating set to permanently kick in if the temp drops lower than 14 degrees Celsius with the addition of a dehumidifier is an excellent way of keeping your home balanced. There is a negligible difference in heating costs unless you have a hole in your wall

From experience you don't want to go any higher than 60% RH as mould becomes a problem. I found this having played with our smaller unit in the cellar.
The cellar is sealed off from the main house and I got fed up of emptying the tank so I fitted a condensate pump and pushed the dehumidifier outlet into it. It pumps the waste water out without any intervention. I'd also fit a pump in the house if I could hide it all away.

 

[Flyfisher]

Our windows are also steaming up, I expect one could collect a few pints in the day if one were so inclined. Consdering that humidity in the house is at 70%+, I suppose that's not surprising, the single-glazed windows are the coldest element, and I'd rather the water condensed there than on or in the walls.

That raises an interesting question in my mind; will condensation form on the coldest available surface or will it occur on any surface of a suitable temperature?

My bet is that it won't seek out the coldest surface (how could it?) and will form on any surface that's below the dew point (but it would be a small bet because I'm not entirely sure).

 

[88v8]

Hmmm, never thought about that.
I guess, when water condenses on the window, initially it reduces the humidity so that the air is better able to retain the remaining moisture. Therefore, it will not condense elsewhere.
But if the windows become saturated, and the air continues to be fed with more moisture from inside the house, then yes, eventually it will condense on other cold surfaces.

Ivor

 

[Flyfisher]

. . . but would it pass by a below-dewpoint surface in order to reach an even colder window?

 

[88v8]

Ummm, assuming one is postulating that our temperature begins above dew-point, and then condensation begins as the temperature falls, I think the cold window would get first dibs at sucking out the water. It might be a photo finish if perhaps there is eg an unusually cold area of wall - wet, north - or localised air volume of greater humidity - eg bathroom, door closed.

Ivor

 

[AMc]

Wouldn't the coldest part of the room would generate the most convection air current past it, more wet air passing by would deposit water there where the temperature difference was greatest?