How good are positive input ventilation systems?
Steve from N.Ireland writes:I'm considering installing a positive input ventilation system like Nuaire’s Drimaster 2000? Any feedback?
Housebuilder's Bible author Mark Brinkley reckons:
Of all the varieties of ventilation systems you can fix into a building, this type has to be the worst.
Despite the rumours, positive input ventilation (PIV) like Nuaire's Drimaster (diagram above) probably won't be overlooked by the revised Part F of the E&W building regs, if only because there are a number of cases where it has been shown to work well. Usually these are on social housing schemes with condensation problems.
However, a new(ish) well-insulated house really shouldn't suffer from condensation problems. At normal relative humidity levels, the dew point is down at around 12°C and condensation won't occur at temps above this. So in this respect, it's answering a non-existent problem.
The only place where the temperature may fall below 12°C is within the roof or the external walls, so it's a good building principle to not encourage internal, moist air into these spaces. Which is exactly what PIV does.
The other major quibble with these single outlet fans (and this goes for the negative pressure fans as well) is that with just one inlet/outlet point, there is ridiculously little control over just where the air is blown or drawn from. Although the diagrams show the air gently wafting all through the house, in reality it's going to take the path of least resistance, which may be straight to or from the nearest trickle vent or badly-fitted window. The larger the house, the worse this effect will be: expect 90% of the house to remain completely unventilated.
Just compare this crude device with the heater/cooler in your car where you frequently have up to six outlets, some of them directional. I think the standard set-up of trickle vents and the odd extractor fan is preferable: they give you more control and are much more adaptable.
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3 Comments:
Hi,
I used to sell these units going back some 10 years ago. We used to offer a 30 day money back guarantee if it did not clear up the condensation problems. I've been to some grim houses with really bad condensation and we never had one single person come back to us for their money back!
They are very effective on houses that were fitted with double glazing without trickle vents as the glazing basically seals the house and allows no natural ventilation to clear the buildup of moisture. I fitted one into my mother-in-laws house going back a few years and it cleared up the condensation problem.
It's not really appropriate for new build though - there better systems available.
Regards, Jon
Would you recommend them for c1900 houses with bad damp?
In the UK I know the main focus is always on heating... but with the global warming well underway this may change. Regardless of that I and friends on mine find our flats too hot even in winter - mainly becasue we want to keep the window closed in the bedroom due to high road noise - so I want something that I can use to get cool air inside from outside. Airconditioning is really not needed most of the time if you can just get the cool air in.
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