Double glazing, ventilation and condensation

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kirschbaum

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# 78339 3-Mar-2011 11:01

Hi all.

I've been thinking. Actually, stumbling on this web page got me thinking about the claims made by double glazing companies about reducing moisture in the home.

The standard line from double glazing companies seems to be that it "reduces condensation on the windows, thereby making your home drier". Now I think they are (deliberately?) confusing visible condensation with air moisture.

Eliminating visible condensation by making the glass surface warmer surely doesn't magically eliminate the moisture, it simply means it's not condensing on the glass.

You still need a way to remove the moisture from your home. These passive vents seem like a perfect way to do this, and you can get them added at the same time you're having your double glazing installed.

I wonder how many home owners are sealing their homes up with double glazing and draft sealing, thinking that they're making their homes drier and healthier...

timmmay

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# 445104 3-Mar-2011 11:13

True. I got Magnetite retrofit double glazing last year - great product, Wellington installers are awful, installers in other areas are meant to be great. The condensation on the windows has gone from saturating a towel wiping each window in the morning to having a very light mist on parts of it, and definitely no puddles on the window sills any more.

You're right that it reduces the symptoms, it's not a cure to the problem. To me having a room where the air gets a bit moist at night isn't ideal but it's not a huge problem either, since I leave the windows open during the day and everything airs out. Having wet windows means you do get mould on the window sills and curtains, which isn't healthy, so eliminating condensation does have big benefits. It also means you don't have to wipe the windows every morning, which saves a bunch of time.

Eventually i'll get a heat recovery ventilation system, which continually cycles fresh air into each room you choose, but takes the heat from the exhaust air and puts it into the incoming fresh cold air, they claim to be around 80% efficient. It works in reverse in summer. I found a great company in Christchurch when I was researching a year or two ago that made great systems that were relatively affordable, $4K or so I think for my place, but I didn't go with it at the time due to funds. I didn't like any of the big brand names systems, and their salespeople are generally clueless and often weren't entirely honest. Talking to me, an engineer, their sales pitches quickly fall apart.

kirschbaum

5 posts

Wannabe Geek

# 445117 3-Mar-2011 11:41

I agree there's a fair bit of dishonesty in the industry. They'll say anything to sell their system, whether it's suitable or not.

I guess it might be a bit much to ask the double glazing suppliers to say "it'll keep your home warmer, but you still need to ventilate". Then again, with these passive vents, they'd be able to cover both angles. Then you'd only need to sort your efficient heating with a heat pump or pellet burner or similar.

I had a quick dig and it seems the passive vents are part of the building code in the UK. You need them in all new windows, and most windows over there are double glazed.

A true heat exchange ventilation system would be great. But where do you live? Would it be worth the investment somewhere like Auckland?

Jaxson

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# 445121 3-Mar-2011 11:48

As above actually.

I did a bit of a home job on our place last winter, wrote about it here:
http://www.geekzone.co.nz/forums.asp?topicid=64936&forumid=48&page_no=3

Photos right at the end are a laugh looking back, but yeah you are spot on.
The moisture is still there, just the windows have warmed and no longer condense the water back to a liquid.

It was interesting to note that double glazing doesn't do this if the room isn't heated. It needs the room heat to heat the air gap so the inside pane is warm. If you don't heat the room the inside pane doesn't magically get heated up from nowhere, so it all stays cold and you get the condensation problem still.

I still have issues with taking cold air from your roofspace in the middle of winter and forcing it into your house. You end up with a well insulated home where you've cut a hole in the ceiling and now force cold air right past the ceiling insulation. To counter this you typically put an electric heater in the duct.

It all seems at odds with one another. First energy saving step is to seal and insulate your home. Next is to force air into it because you've now reduced any air leakage and have a build up of moisture that can't go anywhere. Even then if the house is sealed well then where can this new air go? Up through downlight cavities?

shrub

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# 445134 3-Mar-2011 12:26

I have both double glazing and HRV system In my house I would recommend HRV But the installers are dodgy as and the sales people are even worse. There systems really do work and are not noisy. I have a mate that has the smart vent its alot louder.

timmmay

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# 445154 3-Mar-2011 13:16

Jaxson, you put bubble wrap over your windows? I put a thin window insulation product on mine that looked like glad wrap, worked ok to reduce condensation, but were a bugger to get off. The proper thick plastic sheets work better, mine are about 3-4mm thick I think. Little ugly but I prefer functional.

The heat recovery ventilation systems are designed to avoid ramming cold air into your heated house. It heats the air being bought in with the heat from the air being taken out. So it's not like a pump blowing up a balloon, it's drawing clean air in, and taking warm moist air out, and using the heat from the exhaust air to heat the clean air.

I haven't noticed any condensation on mine no matter what the temperature in the room is, just a very light mist if it's warm inside and really cold outside. If the room's the same temperature as outside you shouldn't get much condensation. You mostly get it when the room is warmer than outside, and has moisture in the room.

Pretty sure this is this company i'll go with, once I get around to it. Reasonable prices, good technology, good products, and based on my interactions with them when I was talking to them, good service.

kirschbaum

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# 445157 3-Mar-2011 13:24

@Jaxson: I agree it feels counter intuitive to insulate and draft seal, and then create openings for ventilation. But I think you need a certain amount of fresh air coming in to replace the damp air.

To take an extreme example, how healthy would it be to live in a completely air tight insulated box? Sure you'll stay warm as there's no "cold" air getting in, but the air in the box will quickly get saturated from your breathing, washing etc.

Compare that to living in a drafty (but weathertight) straw hut. You'll be either freezing your T*ts off or ripping through electricity in the winter, but the inside air will actually have quite a low total moisture content.

So the best outcome is surely somewhere in between. I think you want the building as air tight as possible in its construction. Then you can allow controlled ventilation openings to get the right level of ventilation to keep your home healthy.

Jaxson

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# 445160 3-Mar-2011 13:36

kirschbaum: @Jaxson: I agree it feels counter intuitive to insulate and draft seal, and then create openings for ventilation. But I think you need a certain amount of fresh air coming in to replace the damp air.

I'm not disagreeing with you, just saying not many companies approach this from an overall angle so really everyone needs to be careful when approaching this problem and sorting a solution.

Yes sealing your house off will help with retaining heat.
Yes blowing fresh air in will help dilute the moisture saturated air.

As mentioned above a heat exchanger solution would be best, though there would naturally be some increased fan energy costs/reduced fan performance with having to push past this new obstruction in the air duct.

The balance is how much natural ventilation do you want before you need to start paying energy costs for a fan to force the ventilation. My 1920’s house had no damp issues at all. It leaked/ was drafty as anything and when I tried to heat it I generously tried to heat the whole town surrounding area/town as well.

It's a triangle with Heating, Ventilatin and Insulation and you can't be in two corners without excluding the third.

timmmay: Jaxson, you put bubble wrap over your windows?

Yup, had it laying around and it worked perfectly for testing purposes. Probably better than many other options really for trapping air. Fully admit it looks ridickulous as hell though.

timmmay

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# 445169 3-Mar-2011 14:05

Bubble wrap's a pretty cool idea, except for the aesthetics, it's almost like triple glazing with its air bubbles. It would definitely do a better job than the thin plastic kits you can buy. The hard 3-4mm plastic with retrofit double glazing has some insulating properties, but the air gap is what really does it.

scottjpalmer

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# 445173 3-Mar-2011 14:17

Everyone needs to be aware that the OP "kirschbaum" works for/owns/whatever a vent company.

Matt, don't bother posting the link here or any reference to your company, read the FUG http://www.geekzone.co.nz/content.asp?contentid=1046

Jaxson

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# 445175 3-Mar-2011 14:25

scottjpalmer: Everyone needs to be aware that the OP "kirschbaum" works for/owns/whatever a vent company.

Not disclosing that sort of stuff psses me off.

scottjpalmer

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# 445177 3-Mar-2011 14:36

Jaxson:
scottjpalmer: Everyone needs to be aware that the OP "kirschbaum" works for/owns/whatever a vent company.

Not disclosing that sort of stuff psses me off.

Yip, shady practices are not cool. That is why sometimes we leave exposed scams up and public.

freitasm

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# 445181 3-Mar-2011 14:49

There must be a lot of interest in this industry, because the HRV vs. DVS debates come back here every few months... And invariably there's always someone from within the industry in the discussion (if not starting it, at least getting in later).

Jaxson

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# 445186 3-Mar-2011 15:12

freitasm: There must be a lot of interest in this industry, because the HRV vs. DVS debates come back here every few months...

Yeah I know you and I have both posted follow up threads linking to previous discussions on it.

It (condensation problems) will pick up again for sure because of:

Winter temperatures coming means houses are sealed up more
Newer houses being more air tight and inherently less able to 'breath'
Promotions pushing us to be more energy efficient
Most people still having single glazing which means the glass surface gets cold and more likely to condensate.

I think the standard mould/condensation approach should be something along the lines of:

Find out where your water is coming from first.