Green Building Forum - BRE on PIV - spoiler they don't think it works Tue, 28 Apr 2026 18:46:45 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251701#Comment_251701 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251701#Comment_251701 Mon, 12 Dec 2016 15:55:56 +0000 delprado http://projects.bre.co.uk/positivevent/]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251704#Comment_251704 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251704#Comment_251704 Mon, 12 Dec 2016 16:54:05 +0000 ringi
To quote from http://projects.bre.co.uk/positivevent/ “The occupants were more enthusiastic about the effectiveness of input ventilation than the results would suggest.” The study measured RH at a few locations in the properties; it did not measure RH at the junction between the air and the surfaces that were getting mouldy.

The PIV units may be pushing warm air out of the gaps in the walls, rather than cold air coming in and cooling the walls at these locations, or it may be that the PIV unit just mixes up the air in the property. I think it is reasonable to say that no one truly understand why PIV units work as well as they do….. (Just adding a fun to a kitchen or bathroom can reduce the effectiveness of a PIV unit!)

We are often dealing with building when the tenants will run the heating using the thermostat as on/off switch based on how they feel, along with drying cloths on the radiators!

It is far to say that we all know MVHR installed correctly is a better solution, but that tenants will not pay a higher rent to fund it….]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251707#Comment_251707 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251707#Comment_251707 Mon, 12 Dec 2016 17:21:51 +0000 ferdinand2000
Is it still the case that the loft will be warmer than the surrounding air? Has 270mm insulation in many properties changed this?

I am not convinced of the applicability of results recorded in an unoccupied test house.

Ferdinand]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251709#Comment_251709 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251709#Comment_251709 Mon, 12 Dec 2016 17:34:00 +0000 djh
I don't think the title is a fair summary of the BRE results or their views. Although I don't think BRE did themselves any favours in the way they appear to have conducted the study, or in the way they reported it. For example. they say:

"In the field monitored houses input ventilation was not consistently effective in reducing relative humidity. When absolute humidity excess over that outside was examined it was effective in the most humid houses but did little in the dryer houses. Even in the cases where it was effective there were often inconsistencies between rooms in the same house."

Now it doesn't surprise me at all that ventilation of any kind reduces the humidity more in houses that were more humid to start with. In fact it would surprise me if it didn't. And it doesn't surprise me that there are variations between rooms, but what I would be very interested in is whether there were differences between the starting humidities in the rooms and whether there were correlated differences between the airflows in the rooms. But BRE either didn't measure those factors or didn't report on them, so the whole of the paragraph is pretty useless, IMHO.

The rest of the piece is similarly unimpressive, but they do say "the relative saving is estimated to be a maximum of about 150 Watts in an average modern family house (equivalent to about 550kWh over a heating season, or 10% of annual space heating cost). Actual relative savings will be less than this (possibly even halved)", which I view as stating that they do, begrudgingly, think it works. Whether they used a sensible test or not is another question!

Oh, and then there's the black humour: "The test house was very airtight, with an air leakage rate of 4.5 ach @ 50 Pa having been measured by a fan pressurisation test" :bigsmile::devil:]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251712#Comment_251712 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251712#Comment_251712 Mon, 12 Dec 2016 17:46:28 +0000 ringi Posted By: ferdinand2000Is it still the case that the loft will be warmer than the surrounding air? Has 270mm insulation in many properties changed this?

Most of the time it is due to solar gain, until you start to take much air out of the loft. But some of the air you take from the loft comes from gaps in the ceiling....]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251717#Comment_251717 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251717#Comment_251717 Mon, 12 Dec 2016 18:12:15 +0000 djh Posted By: ringi
Posted By: ferdinand2000Is it still the case that the loft will be warmer than the surrounding air? Has 270mm insulation in many properties changed this?

Most of the time it is due to solar gain, until you start to take much air out of the loft.
But it's warm in the day in the summer and cold in the night in the winter, so not terribly useful, is it?]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251719#Comment_251719 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251719#Comment_251719 Mon, 12 Dec 2016 18:19:44 +0000 ferdinand2000
They are billed as energy saving when they bring hot air in when it is warmer in the loft than the house, which would usually be the seasons when you want it cool.

Still good for humidity and condensation though.]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251736#Comment_251736 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251736#Comment_251736 Mon, 12 Dec 2016 22:36:12 +0000 tony BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251761#Comment_251761 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251761#Comment_251761 Tue, 13 Dec 2016 10:18:02 +0000 ringi Posted By: tonyAnd good for increasing heat losses into the bargain, at the tenants expense too.

Often heating costs reduce when they are fitted, as windows don't need to be left open all the time etc.

Posted By: djhBut it's warm in the day in the summer and cold in the night in the winter, so not terribly useful, is it?


More useful then you expect, as these properties are often heated in the day time outside of the middle of winter. Still the main benefit is that the air being a little warmer creates less drafts.]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251763#Comment_251763 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251763#Comment_251763 Tue, 13 Dec 2016 10:24:56 +0000 gravelld BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251772#Comment_251772 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251772#Comment_251772 Tue, 13 Dec 2016 10:59:45 +0000 ringi BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251774#Comment_251774 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251774#Comment_251774 Tue, 13 Dec 2016 11:00:52 +0000 ringi BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251780#Comment_251780 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251780#Comment_251780 Tue, 13 Dec 2016 11:53:51 +0000 gravelld BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251781#Comment_251781 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251781#Comment_251781 Tue, 13 Dec 2016 12:09:37 +0000 ringi Posted By: gravelldMaybe I live in a dream world but I still don't understand why you need to tell your tenants anything. Shouldn't the house just work? If they boil too much water for pasta shouldn't your humidity meters recognise it, kick in and flush it all out?

Because tenants only care about location, size of rooms, rent level and colour when choosing what to rent.....

We don't live in a world where landlords have unlimited money to spend on things tenants show by their actions when choosing the property to rent are not important.]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251786#Comment_251786 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251786#Comment_251786 Tue, 13 Dec 2016 14:11:28 +0000 CX23882
I'd have thought that for longevity of filters in that kind of environment, PIV would come out a long way ahead by virtue of the fact that it's supply-only. I'm sure for most of us here, it's a moot point, but some people don't treat property with as much respect.

In an MVHR-equipped house that's been rented out by a heavy smoker, what do you do for the next tenant? Replacing the filters is a must, but what about all the ductwork? It's nasty stuff.

But then, would installing PIV result in a loft-space that's covered in cigarette smoke? I'm not sure whether the pressure from the fan would be enough to prevent the cigarette smoke from entering the loft and stinking that up as much as the occupied rooms.

In both of those cases it seems easier to stick to just having opening windows and trickle vents? But then the tenant wants to dry their washing inside "like they've always done" and the landlord gets accused of renting out a property that suffers from "damp".

(this is in no way intended to be disparaging towards tenants in general, more a certain type of tenant, who refuse to take responsibility for their own actions)]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251804#Comment_251804 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251804#Comment_251804 Tue, 13 Dec 2016 17:10:02 +0000 gravelld Posted By: ringi
Because tenants only care about location, size of rooms, rent level and colour when choosing what to rent.....

We don't live in a world where landlords have unlimited money to spend on things tenants show by their actions when choosing the property to rent are not important.That's answering the question "why don't more landlords install ventilation systems", not "why do you ringi not install a ventilation system". Given you have gone the extra mile in doing this yourself I'm wondering why your system doesn't cope with tenant lifestyle. i.e. I'm questioning the system, not your/other landlord's motivation.]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251807#Comment_251807 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251807#Comment_251807 Tue, 13 Dec 2016 17:25:38 +0000 ringi Posted By: gravelldGiven you have gone the extra mile in doing this yourself I'm wondering why your system doesn't cope with tenant lifestyle. i.e. I'm questioning the system, not your/other landlord's motivation.

Because £300 and half a days work is worth it to stop problems, but £3000 is not.......]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251809#Comment_251809 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251809#Comment_251809 Tue, 13 Dec 2016 17:31:01 +0000 gravelld BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251813#Comment_251813 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251813#Comment_251813 Wed, 14 Dec 2016 05:51:53 +0000 ferdinand2000
Any letting house now bought for £100k is subject to an extra £3000 upfront Osborne Tax :-D .]]> BRE on PIV - spoiler they don't think it works https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251846#Comment_251846 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14772&Focus=251846#Comment_251846 Wed, 14 Dec 2016 21:50:53 +0000 ringi
Reduction of housing benefits payments and changes to how they are paid have resulted in most landlords refusing to take any tenants on benefits - hence only the landlords with proprieties that no one would wish to choose to live in are willing to take benefit tenants. Hence market forces have stop working to improve the quality of home at the bottom of the market.]]>