Wednesday, September 14, 2005

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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26 Comments:

Blogger Jon - The Free Golfer said...

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

1:10 pm  
Blogger Bean said...

Would you recommend them for c1900 houses with bad damp?

4:51 pm  
Anonymous Ivan said...

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.

3:00 pm  
Anonymous Anonymous said...

Mark Brinkley reckons, that just about sums up his knowledge of this product. They work very well, I have practical experience of these units for many years on many problem properties. They cure condensation problems (not rising damp) in older properties and normal life style. Don't be put off by these products, they work and are certified!

12:51 pm  
Anonymous Simon Yang said...

My old two bedroom flat have condensation problems. I was suggested to install a passive ventilator in the back bedeoom and a positive condensation control unit in front sitting room. Considering all the rooms normally door closed, can I only install passive ventilators in rooms instead of with positive one? If they both can be reasonble, which installation is more effective? Thanks a lot.

8:36 pm  
Anonymous cheap double glazing said...

Maybe it's a room temperature problem Simon. Ever considered installing double glazed windows? That would help regulate the room temperature.

4:42 am  
Blogger space ranger said...

Bought one a few weeks ago and installed this weekend. Since making the house 'tight' by insulating and repairing gaps round windows (used to roar in winds!) all my decorating has slowly turned black around windows and some walls in my c1900 house. Typical humidity reading was 70-90% according to my trusty weather station from Lidl. Switched on the unit on Saturday now my reading is between 50-60% and ALL my condensation on windows has gone! Yes, in very cold weather it is cool underneath the unit but downstairs seems to heat up quicker and it is not stifling upstairs, plus as we have allergies in my family I'm hoping the clean filtered air will improve our quality of life. Score!

11:14 pm  
Anonymous Villette said...

Ventilation problems can really cause a lot of problems. Hope you are able to resolve it.

Greets upvc windows UK

10:49 am  
Anonymous Armon said...

Proper ventilation and lighting can make or break the livability of a home. You can use double glazed windows to help with that.

4:39 am  
Anonymous Anonymous said...

Had mine fitted sat am took about two hours, and house dry as a bone prev had wet Walls in bedroom in am and windows sopping now not a drip or drop anywhere best 300 quid I ever spent!

7:09 am  
Anonymous Anonymous said...

Looking to get one of these installed but not for the price i have been quoted.
what price would you be looking at for a typical 2 bedroom end terrace house?
£300 sounds tremendous

11:37 pm  
Anonymous Anonymous said...

We have had these Bull shit units installed in combination with this Polystyrene exterior Insulation on our whole housing estate. We have never had any damp problems at all at any time. You can buy these of E Bay for £250 and are just a low powered fan and flexible plastic pipe that pulls in cool-cold air from the loft space to make your upstairs much colder & less comfortable. I have pulled out the fuse and sealed off the hole with Duct Tape and Fibre glass insulation & several others have aswell, what a load of rubbish! they may work very well in Australia where the loft gets very hot but would you then want extra heat upstairs? but not a good idea in windy cold UK.

7:18 pm  
Blogger dipson amatya said...

Does any one help me out , if I install codensation control positive input unit in bedroom ,does this risk to the health??

9:15 pm  
Anonymous Anonymous said...

Try www.pivsystems.co.uk im a local landlord.and have 17 properties which i rent out and each one as a condensation.control unit in which pivsystems fitted.for me i have never looked back hope this.helps

7:59 pm  
Blogger Dave O'Brien said...


just wanted to share my experience fitting a Nuaire Flatmaster with everyone, this could happen when fitting a Nuaire Drimaster too!



I had been quoted £980.00 + VAT from Envirovent and £780.00 + VAT from a Nuaire fitting company. Both prices sounded reasonable but I did a bit of research and found I could buy a Flatmaster on Google with a heater for £320.00 + VAT so I went ahead and purchased it.



The unit arrived the next day, I was then shocked by the complexity of fitting it, which needed to be sighted in a central location and an input vent cut through the wall and various ducting installed.



This was too much for me, so I called Nuaire and they recommended an installation service but he wanted £600!



The solution was obvious call in a local contractor; I looked on Google and found a PCA approved company who was a damp and condensation specialist.



They sent around Miguel (with an invoice of £400.00 + VAT) he sat on the floor and opened the box and read the instructions then proceeded to cut a hole through my wall to install the inlet. The mess was so bad, dust everywhere! He said it was the only way. He then spent time installing the ducting and finally wired in the unit to the main ring. I asked him if he was qualified and said we are Part P approved.



He blew all the MCBs and I could smell burning at that point I showed Miguel the door with his unpaid invoice.



I contacted Nuaire again who gave me condensationcontrol-uk.com phone number who I called, they fixed the wiring and sorted the fan.



They told me installers should be BPEC this is an industry regulation relating to ventilation products.



The summary of the story is always use a proper company or it will lead to problems like I had and even invalidating your insurance by having an unsafe unit fitted.




4:48 pm  
Anonymous Anonymous said...

Yea maybe that's the case in newer homes, but older ones need a bit of assistance with air circulation. This is a cheap alternative to illness from damp air and repair bills from damp walls/carpets! No one ever said it was anything special, but the fact is that the simple fan works wonders for damp, older houses.

Don't be put off! The fact that they are so cheap should only be a further advantage!

1:11 pm  
Blogger Ron hobson said...

I installed one of these myself in 3hours with no previous experience and got an electrician to check I'd done it correctly which I had.
Our house is over 100 years old, we had shocking condensation in the bedrooms and bathroom with mold growth on walls and around the windows and even on the underside of pillows on the beds.
Since this Nuaire unit was fitted 2 months ago condensation has disappeared and the black mold has turned grey and just wiped off with a cloth.
It does make the air slightly cooler but also has an heating element for cold weather.
Its also extremely quiet.
I can't recommend highly enough.

11:56 am  
Blogger Michel Lucy said...

Ventilation problems can really cause a problems. Hope we are resolve it. This problem.

Positive pressure systems

2:01 pm  
Anonymous James O'Keefe said...

I installed a Mr Venty unit back in October after years of mould and condensation. Never heard of Positive Input Ventilation until the chap who sold it to us explained how it worked and guaranteed that it would solve the mould problem. I'd highly recommend getting one if you have suffered from condensation and mould in the past.

4:59 pm  
Anonymous Anonymous said...

I have a bungalow that has a condensation problem. I have just been quoted £999 for fitting a Sovereign Concur nit - with a 5 year warranty. This includes fitting - is this expensive?

2:08 pm  
Anonymous Ken Morris said...

I am a qualified ventilation specialist and laughed out loud on Mark Brinkley's comments. With new homes becoming more airtight it is becoming apparent that there is no where for moisture to exit the building which leads to a build up of condensation and mould. The mould eats away at the very fabric of the dwelling from inside out. I have installed PIV units into both new and old dwellings with amazing results and feedback from home owners, tenants & landlords. Mould requires relative humidity levels to be at 80% over a 6 hour period to enable growth. It is like a plant and grows when fed moisture. The PIV units reduce relative humidity down to a level where mould cannot grow. A family of 4 produce 110 pints of moisture per week through breathing, showering/bathing, washing clothes. In an airtight property how does this moisture leave? The answer is that it doesn't and the PIV unit pushes this moisture laden air down and out of the building through natural gaps. The Envirovent EVL-H PIV system is second to none. These systems also benefit the homeowner through better air quality reducing the risks of asthma. The Envirovent unit is being used throughout the UK by Councils and Housing Associations to rid their properties of mould - very successfully. New build developers are also using this system as it is a cheaper alternative to MVHR systems.

11:20 am  
Blogger Debbie P said...

I've just moved into a house which as this. Can someone tell me why it smells damp with it switched on, and no smell when it's switched off?

11:54 am  
Blogger Debbie P said...

I've just moved into a house which as this. Can someone tell me why it smells damp with it switched on, and no smell when it's switched off?

11:54 am  
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1:59 am  
Blogger Meg said...


Hi I have had a flatmaster 2000 fitted today unfortunately I had a hospital appointment and was unable to speak with the installers, my question is – is the red button on the outside of the unit an off/on switch, also how do I turn on the heater part of the machine as the air seems to be very cold and there doesn’t seem to be anything on the outside of the machine like a heater switch, I had thought it would have a heater and a thermostat to regulate the heat ….thanks for any help you can give me

12:23 pm  
Anonymous Sandra said...

We've had a nuaire drimaster for less than 2 years and this November it started to make a loud humming noise before it stopped working completely. We went back to nuaire as it came with a 5 year warranty and we were told we would still need to pay labour costs to have it repaired as they only cover the cost of the parts that have failed. Had to pay to have another electrician to remove it from the loft so I could send it back to them for a replacement. Ridiculous.

1:31 pm  

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