PIV unit installation

There is a condensation problem in one of my rented properties.
I have been advised to fit a PIV unit in the loft.
Has anyone any experience of these ?
How effective are they ?
Many Thanks in advance

Which room is the problem in?

It’s in the hall, front lounge and bathroom Colin.
One ‘expert’ has advised me that a PIV will solve the whole problem- another has said that I need a bathroom extractor as well.

I have fitted them myself in two properties that I rent.
Excellent piece of kit that does ‘what it says on the tin’.
I would also advise on bathroom fan even without the PIV unit.
When I’ve had to find new tenants I mention the PIV unit and it’s benefits and then it becomes an ‘upsale ‘
Always at this time of year I re-educate tenants on condensation is formed and how to avoid it. This removes any further calls to me regarding black spots in corners of rooms, which in the tenants mind is always damp and a potential health risk!
Always available on line auction site and best go for basic model.
Hope this helps.

I know othing about a PIV. But I do know that a humidity controled fan in a kitchen or bathroom works wonders and I have no condensation problems

Great info Stefan. Many Thanks
What sort of price are we talking (incl. installation) ?


Hi Steve,

The basic units are around £300. Fitted them myself and then got electrician to certify work.

Easy job if your handy with tools and don’t mind crawling around loft space.

Once fitted you you can basically forget about it. Just clean or change filters every few years.

Plenty of info on the ‘web’


Thanks Colin - useful info :+1:

Hi Steve

In our rented house we have a P.I.V. (positive input ventilation) system installed (we bought the house 9 years ago with it fitted) and can testify it does stop condensation/black spot mould growth as two years ago we were between tenants and during re-decorating we switched it off and forgot to switch it back on again when the new tenants turned up. After about 6 months (during winter time) they contacted us saying that they had condensation and black mould spots on the wall and their clothes in our built in wardrobe. We were surprised as our previous two tenants who had been living there over the previous 7 years had not experienced this problem.
I cleaned/killed the mould using "DETTOL anti-bacterial MOULD and MILDEW Remover" and switched the PIV system back on, and after 6 weeks the tenant contacted us to say that their mould/condensation problem had magically disappeared.

I also (as Stefan3 above states) recommend that you fit a good quality HUMIDISTAT type 12 volt bathroom extractor fan which is on low permanently but when it senses steam will automatically switches itself to high and automatically switch itself back down to low speed again when the humidity in the room goes below a set level ie fit and forget and power usage costs is minimal.

The costs vary depending on which supplier you chose.
I have just fitted an “Envirovent” P.I.V. system (middle of the range one) and a Humidistat Fan into the bathroom of my mother-in-law’s 1900’s Bungalow 4 months ago for a total cost of £2,500 (supplied and fitted).
Please note you can purchase cheaper units from other suppliers and save money by fitting them yourselves ie Drimaster Nuaire etc (as the old saying goes “you cut your cloth to suit your pocket”) or as Stefan3 suggests search “on line auctions”.
Following fitting the Humidity and mould problems the mother-in law had have up to date not re-appeared and the humidity of the house has gone from an average of between 65% - 70% down to 40%-55% and the De-humidifier she had which cost a lot money to run 24/7/365 for the previous 10 years has been switched off and consigned to the far corners of the outside garage.

Hope the above info helps you.


£2500 wow. I say again wow

Hi Colin3

Thanks for your tweet.
As explained in my above comments “you cut the cloth to suit your pocket” and as stated the cost included the supply and fit (most other companies only supply the kit and you have to arrange and pay for its fitment yourself) of an Envirovent Atmos Air Source unit with heater and summer bypass complete with 10 years parts and labour warranty plus a Five in One Roof Vent Kit and the fitting of a Cyclone7 12v Centrifugal, low energy, re-cyclable extractor fan with central cartridge with 7 years parts and labour warranty in the bathroom.
The job was completed by 2 local electricians and in about 6 hrs with no hassle or drama and was also certified by them.

Obviously, if a PIV system was required in my Tenants house i would not have spent this amount of money and would have bought a cheaper lower tech version from another company; but this system was required for my 82 year old mother in law’s 1900’s bungalow who suffers from C.O.P.D (a debilitating lung disease).