really stupid Q - ventilation vs warmth

[tycarregydwr]

Hope that subject makes sense. I hope you will permit me to ask this very stupid question, that has baffled me since I moved to the UK, through a variety of flats and properties, but is now especially pertinent as we think about the future of our little stone house. Previously, I always lived in places that were dry and cold as a rule, so the focus was always very much on blocking up any possible source of draughts to keep warm. Now that I live in the land of wet, and I know we have to keep the house reasonably well ventilated to prevent condensation and mould, how do we keep warm?

For example in our previous house we ripped up the carpet, and left the stripped floorboards above the void as they were, having been advised that if we sealed all the cracks we would get damp problems. In this house the floors are all concrete, but for example there are large gaps around most of the doors and some windows, such that the curtains flutter. It would make the house much warmer to seal all this up (at least with weather stripped/caulk and tape as a temporary measure), but it will cut out a lot of ventilation. Likewise, any information on reducing heating bills, etc, always includes those inflatable chimney blocker things to reduce heat loss up an unused flue, but similarly, this will reduce air circulation.

On days when it's not absolutely freezing we usually have a door open a fair amount of the time as children run in and out, and I have always been in the habit of throwing open bedroom windows for 10 minutes after getting up, even in winter. Would this be sufficient ventilation?

Obviously major sources of moisture are cooking - we keep pans covered and use an extractor fan - and drying laundry - we try to do this in a closed utility room only.

I just still don't really understand the balance of ventilation vs. not freezing, and would appreciate your thoughts on this issue!

 

[Roger H]

Good question. When coal was cheap and burning it was relatively innocent (miners welfare not excepted!), a few drafts were a necessary part of supplying oxygen to the fire, helping to change air and draw out damp. In our modern world a green building motto is 'build tight, ventilate right'. I'd say plug up as many unintentional vents as possible and make sure that moist air is properly vented when it needs to be. I intend to fit a mechanical heat recovery ventilation (MHRV) unit to our (currently) unventilated bathroom. This draws out warm moist air and passes it via a heat exchanger among incoming cool, drier air. Apparently at very little running cost. I think this type of system could do a lot to tackle moisture levels and retain warmth in traditionally constructed properties. You can get whole house or single room versions.

'Green Building Forum' has some good discussions on this issue.

 

[worms]

I just still don't really understand the balance of ventilation vs. not freezing, and would appreciate your thoughts on this.

I think this is a problem we nearly all face, so you have my sympathies! I find the best ventilation is the huge throughput of air caused by the Rayburn and the woodburner. Through the winter, when they are running, the house is dry. Through the summer when they are off, the house gets damp. I found that a humidity meter helped me understand how the relative humidity rises and falls with different weather, seasons and household factors.

I intend to fit a mechanical heat recovery ventilation (MHRV) unit to our (currently) unventilated bathroom... Apparently at very little running cost.

But at a high initial capital cost! I'm attracted to fitting one of these, but baulk at the cost!

 

[Andrew Bodenham]

tycarregydwr,

It's not a really stupid question, it's a very pertinent and complex question which troubles many people from architects designers to those living in mould-infested houses.

The current building regs completely fail to address the balancing question, demanding forced ventilation and frequent air changes in one document, whilst demanding a high degree of air-tighness in another. Bonkers.

Old-fangled ways of living involved open fires and draughty windows, providing both heat and ventilation. The use of a breathing building envelope also helped to regulate moisture. Unfortunately it was a hugely inefficient way to heat a dwelling.

In these energy-aware times (and cost-aware) we want to keep warm for less. So reducing the infiltration of cold air by blocking up gaps seems like a very good idea. But at the same time we need to introduce fresh air to displace warm, moisture-laden stale air to maintain air quality in our buildings. Any cold external air that we admit has to be heated, requiring energy. In essence, that's the balancing problem. Fresh and cold, or stale and warm.

There are other complications too. Too much ventilation may reduce the internal temperature of a dwelling, causing problems with condensation on cold surfaces. Uncontrolled ventilation (e.g. vent grilles, airbricks) may admit too much air in windy conditions, but not enough in calm conditions. Circulation needs to be maintained - stale air needs to leave the building as fresh air is admitted. Opening a window when the external humidity is very high can result in dampness inside.

What you really need is to spend all day going round monitoring air-flow throughout the house, internal and external temperatures and humidities, heating demand and comfort levels, and adjusting all your grilles and trickle vents accordingly.

The more I think about this the more convinced I am that mechanical heat recovery ventilation (MHRV) may be the answer. Get the building envelope as airtight and as well insulated as possible. Then apply controlled ventilation to the building, extracting air from areas of high humidity and introducing fresh air to bedrooms and public areas. Extract the heat from the outgoing air to heat the incoming air. Control it all with sensors and a computer. What's not to like, as they say. Just the capital cost, and the hassle of introducing ducting around the house, and running costs, and servicing.

It wouldn't work for some older houses, but it would for many. Has anybody installed MHRV? Experiences please?

To answer the original question - it's not easy, and one that the building industry has not fully solved yet.

 

[Flyfisher]

Not a stupid question at all. I'd say it goes to the heart of many so-called problems with period properties because modern living is so very different to period living and, as RogerH rightly points out, the modern trend is for highly insulated air-tight homes - there is even a pressure test for new homes in order to verify that the air-tightedness meets the relevant standards. A well-insulated and airtight house can be very efficient in terms of energy consumption . . . except that we need ventilation for a comfortable living environment, not to mention control of humidity, combustion appliances and breathing!

I've tried and failed to find the reference, but I've read recommendations that home ventilation whould be sufficient to change the air in normal living rooms 4 times per hour and 7 times per hour in rooms with high humidity such as kitchens and bathrooms. Think about those figures . . . no matter how well-insulated your walls and ceilings or how thick your double-glazing, it's recommended to change all the air in a living room every 15 minutes. All that expensively heated air has to be moved outside and replaced with fresh air at the outside temperature and heated all over again. Every 15 minutes.

Only a heat exchanger system can achieve this sort of ventilation and retain the warmth within the house - fine for a new build but potentially quite disruptive for an existing house, never mind a period house. It's quite a dilemma.

In short, we like to live in old traditionally-built houses but we don't like to live like the old traditional ways because, in general, we're too used to a luxurious living with push-button convenience. This is not intended as a criticism but just to point out that appreciating this potential conflict can help to get the most out of living in a period property.

 

[88v8]

It's a question which goes to the heart of living in an old house.

We're still in our first year in our 1620ish house. I agree with the counter-intuitive finding that it gets damp in summer. Humidity hitting 70/80%. Mmmmmould....
Coming from 30 years in a comfy centrally heated 1920s house, this takes some getting used to. But, I believe one should either get used to it, or get out.
I greatly disagree with the notion of trying to turn an old house into a new one with insulation and draught-proofing. In an old house, character and texture are what matters, both are destroyed by insulation board and modern windows. If one wants modern levels of comfort, buy a new house and put up some plastic beams... which I'm sure you won't.

I believe it is no accident that there has been such a rise in allergies and intolerances. We have not evolved to live in a closed environment, and the myopic trend towards cutting off natural ventilation by labelling it 'draughts' has led to houses which are downright unhealthy. Add to that the chemicals in artificial fabrics and carpets, and household chemicals, throw in the insects that love our cosy airtight houses, and it's not hard to see how this unhealthy environment will play on one's health.

Our expectation of temperature has also shifted. In the not-long-ago, one or two rooms were heated in winter, the remainder of the house was not. People dressed accordingly. Now, too many people seem to think they should be able to wander around in their shirtsleeves all year round. At the same time complaining about their heating bills.

My take... all rooms should have a fireplace with open flue. Yes, including the bathroom, all that damp, although I realise most are too small.
Ventilation around the windows and doors is good, unless the gaps are excessive, because it distributes the air intake the house and its occupants need instead of concentrating it as vents do.
Curtains.... research in Scotland found that curtains (or shutters) can be as effective as double-glazing. Yet how many people don't bother to pull the curtains, or even have none? Or they hang over the radiators... doh...
http://www.yougen.co.uk/blog-entry/1406/Close+your+curtains+to+keep+warm+'28and+reduce+bills'29/
Indoor temperatures above 60f (16C) are unnecessary. Dress accordingly. In the winter, I routinely wear two pairs of socks, a T-shirt, a shirt, a wooly... indoors. When it's cold, add a vest and a pair of long-Johns.... indoors. And did I mention bedsocks?

Where does all this leave you... you're on the right track. Ventilation... heat... open fires... 3-5 air changes per hour. Dress accordingly.
It also helps if you drive an appropriate vehicle, it will make the house seem warmer.

Ivor

 

[tycarregydwr]

Thanks everyone.

We definitely have different-than-average expectations about internal temperature, in the winter we find 17-18 degrees C to be toasty warm. We usually only heat in the evening, only adding a morning heating cycle once the kitchen is routinely 10 C when we get up. So we're certainly not expecting 'modern' levels of cosiness. But with two young children, I do worry a bit about when too cold is too cold - the 5 yr old sleeps in his own room and is already wearing a wooly vest, fleece pyjamas, sleeping under a thick woolen duvet and a woolen blanket, and it's only October! The toddler I'm not as worried about as she's in with us, but she's already in a sleeping bag and under our duvet....

We will be sticking with our thick curtains and some weather stripping for now and continuing to meditate on this whole issue.

 

[worms]

On the topic of ventilation...that is quite some ventilation system on your Land Rover! I assume this is the 88V8 and the brass covers allow air in to a pair of SUs?

 

[tobydog]

One of the downsides of having our contempory kitchen extension attached to our C17 timber house by way of a link hall is the huge variations in temperature between the two buildings. Before, when the old house was cold, we dressed for it and acclimatised accordingly, however, we now feel / notice the cold much more when going into the old part for the evening. Last year at Christimas when all of us (8) were in the extension we actually had the door open. Go next door and it was a different story.

Extra thick curtains over the doors will play a huge part this year. We've tried those so called thermal / blackout curtain but they are hopeless. I'm thinking of having a summer tog single duvet sown onto a curtain or is that excessive?. I feel I should be plugging the gaps around the doors but I totally agree with Ivor's take on the issue. With thick curtains we will benefit from the insulation but moisture still finds its own way out of the gaps when it finally becomes drier outside. The winters of 2009/10 and 2010/11 were quite dry and the house never felt damp.

Tycarregydwr - I was 6 months old during the infamous UK winter of 1962/3. We lived on top of the North Downs in Surrey and had no central heating. Temperatures went off the scale downwards. We had snow drifts higher than busses in places. Apparently my mum would put me in the cot and leave the window open :shock:. There were no thermals in those days, just woolen blankets. Some younger generations would call that unhealthy but I don't think it did me any harm. If young children start to complain they are cold then I think you need to take care but too often you see very rosey cheeked young children that parents have smothered in the belief that they might get cold!

 

[tycarregydwr]

I spent most of my formative years in the north-east US, winter camping in -25 C, and then lived in Moscow, with frequent winter temps of -40 C, so I know cold! But damp cold is a whole new ballgame...

 

[CliffordPope]

As others have said, this is a very sensible question, and one I still haven't really answered after 26 years of living in an old house.

If you have full central heating and don't care how much heat/money/energy you waste then just turn the heating up in every room as hot as it needs to be to drive the moisture out.

But realistically, if you enjoy an old house for what it is and don't want to squander money, then you have to accept compromises. It also needs discipline from family members. If someone has a bath or shower, keep the door tight shut, and when finished open the window wide to let the steam and humidity out. You could use an extractor fan, but if it is powerful enough to pull all the steam out it will be jolly cold bathing with a forced gale raging over your head.

Also you have to constantly aware of the comparative humidities of outdoors and inside, room by room. If a room is damper inside than out, then you have to either open the windows and shiver, or get the temperature up to a point where air with that quantity of moisture can hold it in suspension and not condense it on cold surfaces. If you are doing that, then keep its door shut. Releasing warm moist air into the rest of a cold house will simply direct it to the coldest parts, where it will condense.

Another compromise I made early on was to rely on dehumidifiers. It feels like cheating, and not very "green", but they work. When you empty the container of several pints of water, reflect that that is water that otherwise would have been on your walls. Imagine filling a garden sprayer and walking round the house squirting water mist over every outside wall, because that is where it would have been without the dehumidifier.

 

[tobydog]

Okay tycarregydwr, you trump me even if I was only 6 months old!

We have one of those hurricane extractors in our bathroom and we also now use a dehumidifier, however, we still steam up too readily. We are fighting a losing battle, at least this year, with it being so wet outside. We also have some open plinth work in the old kitchen that's not helping. There is a thatched cottage a few doors down from us that never steams up anywhere even when they hang washing up inside. I need to find out what their trick is. I plan to open up selective parts of the impermeable felt under our thatch to try and eleviate matters. I know this can cause problems when the thatch starts coming to the end of it's life and leaks but I'll do it in a way and place where the impact is minimal. A thatcher is currently working on repairs and has made suggestions. This should certainly help with ventilation.

 

[tycarregydwr]

SOme really interesting replies here, thank you! It's very relieving to hear that this is something other people still struggle with, and not the case that I've simply missed something obvious.

 

[Feltwell]

On the topic of ventilation...that is quite some ventilation system on your Land Rover! I assume this is the 88V8 and the brass covers allow air in to a pair of SUs?

I was going to ask the same question - is that a novel way of getting air into a Rover V8 that's been shoehorned into an old lightweight?

 

[worms]

I was going to ask the same question - is that a novel way of getting air into a Rover V8 that's been shoehorned into an old lightweight?

Shoehorned indeed! I'm amazed that there is space without moving the grill forward (unless it intrudes into the cab! Or perhaps we need to think laterally and not assume that it is the rover 3.5 V8 but something much smaller?).

Come on 88v8, as they say elsewhere on the forum - "we need pictures"!

 

[JoceAndChris]

Lovely topic. My house is freezing and draughty, with old rattly sash windows, a glass porch with leaky doors, 5 open fireplaces, bare floorboards over earth, and a huge roof void we're still working on filling up with insulation. The heating doesn't really make much difference so we don't put it on except for 15 mins a day to heat the water.

There isn't any condensation or damp, and I wear thermals, thick woollen dresses, layers of cashmere and a Toscana fur hat. I sit by a fire indoors or work outdoors.

A bit of curtain advice for tobydog - you need to choose a heavy top weight, like a nice thick velvet, or woollen plaid, or heavy damask. The interlining should be this one:

http://www.merrick-day.com/acatalog/Interlining.html

It's a wonderfully heavy, bump interlining at 410g per sq m.

The lining should also be solid and insulating, I'd go for 100% cotton sateen at 125grms per sq m.

http://www.merrick-day.com/acatalog/Merrick___Day_100__cotton_lining__17.html


I'd also try to build a top treatment into the design - a pelmet board or swags and tails to stop the cold creeping up the top.

The Georgians made the whole thing even warmer and more flexible by starting out with a Roman blind and putting the curtains and swags and tails around that. Men would wear a turban and coat indoors (a banyan for relaxing in) and women wore turbans too, as well as shawls that were in fact more like huge, warm blankets that wrapped right around the body. Modern people generally don't know how to dress their windows or themselves.

 

[88v8]

On the topic of ventilation...that is quite some ventilation system on your Land Rover! I assume this is the 88V8 and the brass covers allow air in to a pair of SUs?

Yes and yes.
The theory is that they allow cool air in and hot air out, at the same time of course. Air is very well organised like that.

Mmmm, pictures. Oddly enough, haven't taken many as it's not awfully photogenic, I'll see tomorrow.
One reason the Rover V8 fits is that the installer - 1992 - moved it back eight inches in he chassis, as reckoned by the position of the gearbox mount.
Mind you, my previous 88V8 also had the standard rad & grille, but a short-nose water pump.

Ivor

 

[Alex]

I know what you mean tycarreg, we have spent the last 26 years in Wales with the damp cold winters but last winter we were working away from home in Teesside, it was completely different. We were a 10 minute walk from the beach and I spent every evening on the beach with the dog, no matter what the weather was like. When it was cold and there was an icy wind blowing off the North Sea, (we went to the beach one evening and the sand was frozen, the dog refused to walk on it) it never felt the same as that cold damp Welsh winter. There is a real 'damp' difference between the UK's East and West coast in the winter.

Alex

 

[billybuntus]

We live in an old house which is sub 10c when not heated which makes for a very frosty living environment. When we first moved in we found external corners in most rooms had black mould (condensation). Any warm air would hit these extremely cold spots and condense. The house is a large 3 bed detached.

Over the last year we've introduced a large dehumidifier (about 600w on full pelt but we always leave it on half setting). It doesn't have a humidity % setting which would be helpful but its all we have for now. I leave it on all day every day. I empty its 3.3Litre tank which fills without fail everyday and has done for a year then I turn it off. I fire it up again before leaving for work everyday.

We leave our boiler (A Baxi combi 105e) on 24/7 - 365 days a year. The manual thermostat is never set lower than 14 deg c. It never kicks in during the day until its 5c or colder outside generally. It just say keeps the chill off the house through the winter and prevents condensation issues. When its cold outside (october to feb ish) we turn the heating up after 6pm until 10pm to around 18-20 deg c.

We've estimated it only costs around 10% more at most when compared with our previous trials of turning the heating on to 18 deg c everynight through the winter without leaving it ticking over through the day. The reason being the boiler doesn't have to heat a huge mass every night.

I've since started insulating the really cold walls of the house (its a stone building) by battening the walls and dropping 1 inch celotex in between then drylining over.

I've done both external walls in two bedrooms up until now and the rooms are much more comfortable with an added bonus of being able to turn down the radiator thermostats in each room. I've left the adjacent internal walls along as they weren't as cold to the touch.

I think the key is getting the balancing act right in an old house and using modern materials wisely. I certainly don't want to live in an air proof old house. I just need to make the house comfortable to live in.

A dehumidifier in an old house is essential in my opinion.

We also have an open fire in the sitting room which we put on at a weekend. There's actually really no need when the heatings on but its cosy and looks nice

My energy company predict my electric and gas over the coming 12 months will be £1250 and they were accurate last year. Just to put it into financial terms in case people think I'm spending a fortune on energy.

 

[Feltwell]

There is a real 'damp' difference between the UK's East and West coast in the winter.

I was 10 when my family moved from Norfolk to Cheshire, and my parents still complain about the difference in weather. As a kid I didnt really notice it, but their comment was that Norfolk was a "dry" cold whereas in Cheshire it's always damp. You certainly got plenty of damp, misty/drizzly days where they lived in Cheshire, whereas in Norfolk it seemed to either rain properly or not rain.