Positive input Ventilation units – What is your experience?

I retrospectively fitted trickle vents on one of my flats. Really simple, you just buy the vents online (Amazon etc…very cheap) then drill a line of holes through the frames and screw in the vents. Use a sharp drill bit and be careful as the drill can bite. Not a game changer but they do help.

I researched electric vents and have bought a Blauberg Vento (£400), which we’re fitting tomorrow (needs a sparky). It sucks air in and out every 70 seconds via a heat exchanger so is very efficient. My architect has one in his kitchen…one day he came downstairs and the external glass was soaking…turned out they’d had a power cut which stopped the fan. So they must work. Expensive to buy and fit (including having to buy a 182mm core drill, £85!) but I have high hopes this’ll do the trick.

I did look into this and there are stories of success but in the end I went with ( so offer as a consideration ) dehumidifiers which have been a game changer. Tenants love them and they work very well.
I found PIV to be a pricier option and a bit of a pain to retrofit. Maintenance was also a factor. Dehumidifier units for a decent one if you shop around £150. I supply 2 per flat.

PIVs can help to mask problems with a property or with a tenant’s failure to keep the property warm and aired. They shouldn’t be necessary.

I have fitted over 50 PIV units over the years and found them to be an excellent way of reducing condensation, particularly in houses with solid walls. I also retrofit trickle vents to windows as well if the houses do not have them as it creates a good cross flow for ventilation.

My feedback from tenants is that dehumidifiers do work but that are very costly to run, several £ per day. PIV's on the other hand, only cost about £10 per annum.

Our experience of PIVs in a few properties has been very positive and we have definitely seen a difference between those that have them and those that don't. Plus, it means we do not have to rely on tenants "promising" that they follow all the condensation rules......They have worked for us.

Reply to the comment left by Andrew McCausland at 26/11/2024 - 10:43
Given that dehumidifiers are only operative in the winter, they cost very little to run. Every watt used by the device contributes to the heating of the property and reduces the heating from the fixed heating source. The same goes for refrigerators, although of course these are operative all year.

Word of caution.
I have fitted NuAire in the loft space and pipe it to where required
It automatically switches off when the temperature of the module exceeds 25C.
This happens quite a bit in the summer.
Often only comes back on about 0300.
The roof is directly south facing so that makes the issue worse.
However it is fully covered in PV panels which act as a barrier to the heat therefore improving the way situation.
However overall very pleased.

If this is an old upvc double glazed window I would suggest you might have an external maintenance issue. Seeming as damp has spread further into the wall/plaster than just the cill.

Older windows were often mounted in a wooden frame. Externally silicone was applied between the frame and render on the opening. Either the silicone, render, or both have failed. Excess water enters here and gets stuck, condensing internally. It can also rot the wood frame.

Also, you can retrofit trickle vents. It's easy, basically drill a hole through the frame.
Fitting a PIV might mask an underlying issue. I think it can also impact your EPC rating.

I'm a Passive House Consultant focusing on retrofitting older houses to be more energy efficient.

What is the age of the property? I'd be extremely wary of installing a PIV in a pre-war property. PIVs mask the underlying cause of the excessive humidity by pushing the warm, moist air out of holes in the building envelope. You've already stated that the windows don't have trickle vents, so the air is going to find another way out, which in older properties is highly likely to be around the intermediate floor joists, or through a suspended ground floor. This brings that warm moist air in contact with cold surfaces, where we then have the potential for condensation, mould and eventual timber decay in unseen areas. PIV is a short-term sticking plaster, but doesn't sort the underlying cause. Additionally, it's bringing in large volumes of cold are through the roof that then needs to be tempered at additional cost.

Do you have extractor vents in all the bathrooms and kitchen? Is there a 10mm undercut on the bedrooms doors to allow cross-ventilation between rooms (assuming they are not fire doors)? Try and capture and remove the humidity at the source, so it's not attracted to colder surfaces such as windows.

Are there any leaking gutters, pipework or cracked external render that might be allowing additional moisture into the property? Have the air bricks been sealed by someone thinking they are reducing draughts, but in fact allowing a build-up of moisture under the floor? This is less of an issue in modern buildings with a DPM.

Reply to the comment left by Robert Locke at 26/11/2024 - 14:24
Your expert advice indicates just how tricky it can be to counter someone who will not ventilate properly (i.e. open a window).