The problem is that as many landlords know PIV clearly works well, in that when you fit it, there is less mould on the walls and the tenants are happier! Fitting a PIV unit is also easy and relatively cheap, but sometimes (say 5%) does not work.

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"

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"

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?

And good for increasing heat losses into the bargain, at the tenants expense too.

I do worry about the loft air. There's some nasty stuff in there. I realise they have filters, but the haters kick off about MVHR filters so we can kick off about PIV filters too right?

PS, please give me a full MVHR system in my own house any day, but I am willing to pay the additional cost of having one.....

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.

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.

Ok, so the answer is this can be done and the only reason is money?

There is also the restriction of tax offsetting of mortgage interest, so landlords have much less limited capital.

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.