Positive input ventilation units

[hunta]

I know there are those around these parts who like to get stuck into a building issue so here goes...

We have a good-sized family house which, being a 70s build with single pane sash windows, suffers from a bad case of condensation outside of the summer months.

This is our second year in the house. Last year we'd had a load of building and decorating work done, so we were expecting moisture to be an issue. We're careful not to generate too much moisture (tumble dryer rather than line drying etc.) but still there's full condensation as opposed to fogging on the upstairs windows when the temperature starts to drop so I'm looking into potential solutions. .

1. Double glazing - the obvious and most expensive option, but likely to be the only full cure (?).
2. Dehumidifer - ran one last winter and never really got used to the noise, or the feeling of fighting a losing battle as we were still wiping the dew off the inside of the windows most mornings. Also has running costs to take into consideration.
3. PIV - I like the low running costs vs dehumidifer and initial outlay vs double glazing, as well as the idea of some air circulation, but I'm unconvinced about how capable they are of making a meaningful dent in the condensation issue (despite what the salesmen might tell me).
4. Double the heating bill.

So, I guess the first question to answer is how much of an effect can PIV units have on window condensation?

 

[CraigJ]

I fitted a PIV in my old 3 bed semi as we were getting the same problem of the windows being wet in the mornings. It got rid of the issue almost completely on the first night and by the end of the first week the house was dry.

I fitted a Nuaire Drimaster. You can get them with a built in heater too. Ran ours on the midddle setting and you could not hear it.

My folks also had one fitted to there bungalow due to wet windows and again it cleared it up pretty much right away.

 

[rockits]

One thing to know about condensation. If you fit double glazing then all you are doing is stopping the condensation appearing on the glass. It doesn't disappear and still exists just moves elsewhere.

Condensation if it exists will always appear on the coldest surface it finds. So by fitting double glazing it means it will stop appearing on the glass but still exists on the next coldest surface which is often the back of a wardrobe or similar.

Dehumidifiers are a better way to reduce the moisture in the air and control it. Most modern dehumidifiers have a setting of %RH so it doesn't become too dry. Dessiscant ones are a little less efficient but have a nice advantage as kick out a little heat so act as a little heater which is useful. I have dehumidifiers in garage and polytunnels and they work well set at 55% RH so just come on when they need to.

Secondary glazing is still a very cost effective way to improve window efficiency beyond that of double glazing and easily out performs it due to much larger air gap. I spent a few years making windows for my dad's business before going into IT!

 

[rockits]

There are two issues here as well. Condensation but also creating a healthy air state with so many changes of air per hour/day Most modern houses now have low quality air as are too well sealed so have stale air due to not enough changes of air. It is good to have some vent/gaps etc. to provide natural changes of air. I can't remember the figures as I worked with windows 25-35 years ago but depending on house size, contents and make up you need so many changes of air per hour/day to create healthy air. I still work with fecking Windows now just a different type so can't get away from the word!!

It is a case of finding the root/source cause and resolving/improving this and not masking the problem. Brick walls with no insulation is never going to be great. We have come a long way in building in not so many years which is all good. There are lots of coated glass and gas filled cavities that really can make a big difference in efficiency of a house.

I know a house built near us recently all nice and fancy with lots of steel/glass. The idiots have not used any very high performance glass with massive expanses of it. This summer it was unbearable for the owner but would have been good for them to grow fruit/veg! I have no idea how these pass building regs.

 

[Zep]

PIV (or Heat Recovery Ventilation as I call it) is the way to go. Lowest running cost (just a couple of fans) vs much more for dehum. The initial cost is the highest of the options but over several years it will pay back and more. It also has the benefit of improved indoor air quality.

As the outside air has a low absolute humidity so has a low relative humidity once heated up to room temperature by the heat from the extract air. You can have the extract from high humidity areas like the kitchen and bathroom and have the new dry air pushed into the living room and bedrooms.

As others have said, if you have high humidity if you solve the window condensation problem with double (or secondary) glazing the issue can move to other areas. This will only happen if you have cold spots in the house (uninsulated external walls etc) as the temperature of the surface has to be below the dew point for condensation to form.

 

[GeoffCapes]

This is Zep's area of expertise so whatever he said!

 

[Navcorr]

It is a case of finding the root/source cause and resolving/improving this and not masking the problem.

+1

Sash & Case are notorious for leaking. With Scotland being a touch drafty, indeed some might say a little breezy at times, improving their performance could be a big help. Given Sash & Case are the traditional style here almost everyone I know have had theirs renovated.

 

[Zep]

+1

Sash & Case are notorious for leaking. With Scotland being a touch drafty, indeed some might say a little breezy at times, improving their performance could be a big help. Given Sash & Case are the traditional style here almost everyone I know have had theirs renovated.

Absolutely, assuming there is a root cause that isn’t just using the shower and cooking in the kitchen. Or for that matter pesky humans breathing out moist air.

 

[Navcorr]

A fair assumption to make give the OP's comments. Most household sources tend to be localised for a relatively short period. Albeit annoying at the time. Whereas this appears to be more serious.

 

[Felonious Crud]

PIV (or Heat Recovery Ventilation as I call it) is the way to go. Lowest running cost (just a couple of fans) vs much more for dehum. The initial cost is the highest of the options but over several years it will pay back and more. It also has the benefit of improved indoor air quality.

Does this work on leaky creaky old timber-framed houses as well, Zep?

 

[hunta]

I don't think there are any addressable root causes remaining. We had decent extractor fans fitted as part of the bathroom renovations, cook with the extractor hood, tumble rather than line dry etc. We do breathe when we absolutely have to.

The sashes were renovated and fitted with draught excluders last summer too, though we have experimented with leaving them cracked.

 

[zagatoes30]

We do breathe when we absolutely have to.

Well there's your problem

 

[lifes2short]

are you heating the whole house properly to a comfortable temperature, lack of proper heating can be a problem on its own

 

[outrun]

These are useful, stick one on each badly affected window ledge. They pull water vapour out of the air. We have a similar issue in one room only which is caused by a poorly insulated contact with a stone external wall that is always in the shade so the sandstone never really dries. Walls and structures need to breathe and the best way of doing this is to open windows every day for a decent period of time. Granted this can be a security issue when you're not in but it's the best way to challenge air quality. PIV is great if you have suitable loft space or similar to install in to. We don't have that so I have to rely on other methods. Our house is triple glazed all round which causes it's own issues as mentioned by others but one of the silly ones is that in the rooms with roman blinds (my wife's favourite style!), the trickle vents are limited as the blind is always in the way. Ideally ensure that any vents are free to allow air to get through. We also have a window seat/storage unit in one of the areas of issue and that has been painted internally with bathroom paint that helps restrict the formation of mould spores. Spores can be harmful to those with conditions such as asthma and so keeping window corners and the like cleaned with a light bleach solution is important for health.

If only we lived in a dry, hot climate....

https://www.amazon.co.uk/gp/product/B00I3VKBJS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Double/triple glazed windows with a top opening section can be opened about a centimetre and then locked which is good for security concerns. Some folk don't realise you can do this!

 

[hunta]

are you heating the whole house properly to a comfortable temperature, lack of proper heating can be a problem on its own

In short, no. We have per room zone control so only heat rooms on an as required basis.

 

[hunta]

PIV (or Heat Recovery Ventilation as I call it) is the way to go. Lowest running cost (just a couple of fans) vs much more for dehum. The initial cost is the highest of the options but over several years it will pay back and more. It also has the benefit of improved indoor air quality.

As the outside air has a low absolute humidity so has a low relative humidity once heated up to room temperature by the heat from the extract air. You can have the extract from high humidity areas like the kitchen and bathroom and have the new dry air pushed into the living room and bedrooms.

This sounds like a more sophisticated (and therefore expensive) system than the Nuaire, which I thought just take air from outside, or have I misinterpreted?

 

[CatmanV2]

https://www.amazon.co.uk/gp/product/B00I3VKBJS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

I've tried about every variation of those over 20 years, and never *ever* had one make a blind bit of difference, and yet some people swear by them. Very curious.

Had them in the 4200 a few years back. They didn't even go pink over the entire winter.....
...yet the car steamed up every morning like a sod (and the heater matrix wasn't leaking)

C

 

[Navcorr]

Which begs the question

 

[lifes2short]

In short, no. We have per room zone control so only heat rooms on an as required basis.

that might be the problem, heat the whole house and see if it resolves it, especially important in older houses with small cavities walls and/or no cavity or insulation, had this issue with the student lets, they always switch the rads off in some rooms and then wonder why they have damp and mould problems, bless em

 

[rockits]

We have an old 400yo cottage and have no zoned heating control. However this helps as we heat the whole house. We do have TRV's on the rads so lower the unused rooms and increase the used rooms. We don't get much damp or condensation short of a bit on the glass in morning in bedrooms. However a few mins of opened windows in the morning and it's gone.

New houses with new high tech systems and thoughts tend to keep house permanently heated at low temp only needing small amounts of energy to boost to higher levels. In essence it never gets cold and damp. Underfloor heating and very efficient insulation is essential for all this to work correctly though.

Are bottoms of walls especially external walls cold/damp?