Positive Input Ventilation – testing in York

Here in Yorkshire, we are well into the ‘condensation season’.  That period from around late September to March, where the majority of clients asking for ‘damp’ inspections are really plagued by mould growth, caused by condensation.

Of course, excessive condensation is a growing problem, especially now that the government has decided that heat loss is more damaging to us, than the consequences of breathing and re-breathing stale and humid air.  Which is something we never evolved to do.  Anyway, I digress.

One growing weapon against condensation problems is the Positive Input Ventilator (PIV). PIV’s work on the basis of drawing in air from outside a property, filtering it and introducing the air into the house.  This has the effect of diluting the moist air inside the property and encouraging the house to ‘bleed’ this moist air, via gaps under doors, air vents and such.

In practice, I can vouch for the success of the approach, particularly in ‘problem’ properties, which haven’t responded to normal measures; fans in the bathroom/kitchen, advice to tenants about drying clothes and such.  Examples include student lets, where half a dozen girls, sharing a terrace house, seem to make as much dew, as a hectare of Amazonian rainforest. It’s all that hair washing malarkey…..  I’ve used these units in Leeds, York, sheffield and Wakefield and they’ve always worked.

However, anecdotal evidence is one thing – data is another.

So, next week we are scheduled to install a PIV in a bungalow in York, North Yorkshire. I’ve previously surveyed the house. I diagnosed condensation/mould growth, caused by excessive humidity, through poor ventilation and an unusual house layout, which compounds the problem.  I gave advice at the time, but the landlord of the bungalow is impatient to see results; this winter.  So on Tuesday we install the PIV.  It is a basic model, going in the loft, with the ducted vent in the central lobby ceiling.

Keen to see data on how things change, I’ve installed two data loggers at the York address today. Hopefully we’ll have data: for a few days before the PIV installation; a week or so after installation and then; with the tenants cooperation, further data, which will monitor the effects of extra simple measures to increase the effectiveness of the system.  I’ll be using a Psychrometric chart to calculate the vapour pressures inside and outside the house, for the whole experimental period and will publish the results here.  There’ll be video footage and images of the data too, for those who are interested.

condensation data from York

I’ll be back to the house in a week or so to collect the data and blog the results.

let’s see what happens….

Dry Rot.

PS – part 2 is ready here


  1. The Grim Reaper says


    Let the loggers run for 4 weeks – a week is a little short (unless really pushed)

    • Dry Rot says

      Yes – I agree but I only had the idea to do this last thursday so we’ll have to go with what we’ve got. It’s just a bit of fun.

      Dry Rot

  2. George Dunnett says


    Thanks you very much for the video clip. It was very informative.

    I have used a Protimeter hygrometer with the side surface temperature sensor for some years now, to help give tenants and owners of houses with condensation problems a little more numerical evidence to help them understand what’s going on.

    I’ve found that once you tell the occupier how close the wall is to a condensation situation they suddenly become very interest in the subject. Another Eureka moment.

    I quite agree with you about young women in tenanted properties. Wall to wall wardrobes full of clothes and shoes double glazed windows, curtains shut and the radiator covered with damp towels.




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