This is a short post on why it is necessary to get a positive input ventilation system installed professionally. There is an actual qualification in ventilation, it’s a Bpec – Domestic Ventilation Systems, I have also attended the Property Care Association Masterclass on ventilation, all of this gives me an understanding of how to install and what to look out for to ensure the PIV will work to the best of it’s ability. I have also data logged many buildings before and after PIV installation, carried out thermal imaging and generally seen how these units work.

I was called to a property where they recently had a Nuaire Drimaster installed, this was purchased cheap on line and was fitted by an electrician.  The property had an extract fan in the bathroom and the kitchen which were not working, after some research online they decided upon purchasing a piv unit themselves and getting there chosen electrician to carry out the install.

The below graphs show with the positive input ventilation system switched off and then with it switched on. It may appear that it has actually worked, but if you notice the external vapour pressure has decreased during the monitoring period which has subsequently reduced the internal vapour pressure, the internal vapour pressure is the sum of the internally produced water vapour plus the external vapour.

data logging on how to install a drimaster  VAPOUR PRESSURES after a positive input ventilation system was installed monitoring a positive input ventilation system monitoring the internal environment by data logging LIVING ROOM, TEMP, RH AND DP blog

The gable wall of the roof kept falling below dew point and condensation was occurring, this looked like penetrating damp as it was running down the walls into the bedrooms. You can also see the ‘mean’ of the external temperature and the roof temperature, showing an average of 3 degrees difference, being warm in the roof.


Unfortunately the electrician didn’t install this correctly, I don’t want to go into detail on how I get the best out of a PIV as i’m sure my competitors could read this and pinch my tips…….One thing I will say it is imperative that the roof is well ventilated, vapour goes from high pressure to a low pressure gradient, any leaky parts of the building will allow this vapour to move out of the building. What many  people fail to realise is how much of this vapour will go back into the roof through the plasterboard and also the loft hatch, it will also go into a suspended timber ground floor. I find many  installs are literally just re-circulating the air from the building into the roof and then back into the building, an excellent way to measure this is by data logging carbon dioxide co2. By measuring carbon dioxide we can actually tell how much air is being replaced by new fresh air externally, carbon dioxide levels externally are under 400ppm. Another thing about why we bother with ventilation is that most people think they need rid of mould and condensation issues, which is correct, but also one of the most important factors is fresh air. It is well documented now about indoor air pollution, high levels of co2, volatile organic compounds (VOCs), this is proven to be bad for our health. 

An example below.

Some experts are concerned teenagers are over-using deodorant, warning that inhaling chemicals from the aerosols may cause allergic skin reactions, asthma and breathing difficulties.
In very rare cases they may even trigger fatal heart problems.
Maureen Jenkins, director of clinical services at Allergy UK, says: ‘Around one in three adults in the UK have some form of allergic disease — asthma, rhinitis or eczema — and their symptoms are easily aggravated by perfumed products and exacerbated by aerosol chemicals.

Even people without allergies can be sensitive to chemicals found in cleaning products or toiletries, experiencing skin reactions, breathing difficulties, nausea or headaches. The reactions are made worse when it is an aerosol as the fine mist is easily inhaled.’
Dr Peter Dingle, an environmental scientist and consultant toxicologist based in Perth, Australia, says: ‘The labels on deodorant aerosols instruct you not to use them in a confined space, but I think it’s safe to say most people in the UK aren’t going to go outside to spray on their deodorants.
‘They would do it in the bathroom, most likely with the door closed — and that’s a confined space.
‘In the middle of winter, you’re not even going to have a window open. If you watch a deodorant advert, the young man usually sprays himself all over his body, which is exactly what the can tells you you’re not supposed to do. Self-image and smelling right is all important for young men and there’s a lot of peer pressure to use these products.’

Basically if you follow the well documented Building Regulations Part F, it gives a clear guidance on ventilation systems and the necessary air changes.

If you need a positive input ventilation system installed correctly please contact us to discuss. We offer the Envirovent Mr Venty, the Nuaire Drimaster as well as the Elta positive input ventilation system. We also install extract fans, from humidistat type type to contact trickle extraction fans. We also offer heat recovery and the new alternate single flow and extract ventilation with heat recovery to habitable rooms. We have had great success with our latest installs and great feed back.

Click on this link, this has some interesting links on it that could be of interest to you regarding indoor air pollution

Contact Complete Preservation for your survey, we can eliminate mould and condensation and provide clean air to your building. 01225 769215

Posted by Complete Preservation


  1. Hi
    I had a PIV unit installed after having a guy come out to me to undertake a damp and mould survey, using thermal imaging, etc. Anyway, long story short, after following up his recommendation of a PIV installer, I had a Flatmaster 2000 machine fitted into my loft; I later found out from the manufacturer, Nuaire, that these shouldn’t​ be in lofts, but​ fixed to exterior walls; and I am now having trouble with getting an appropriate machine to replace it fitted by the installer, who I notice also hasn’t provided me with a Domestic Electrical Installation Certificate of some kind. Looking at Nuaire’s website, and what I have downloaded from it, it appears that only qualified electricians​ should be fitting these things. But I don’t know for certain if their installers are required to provide electrical certificates to comply with building regulations, etc. Can you confirm, please, if that is so?
    Many thanks in anticipation of your helpful advice.


    1. Hi Karl, the info you have been given is correct. Unfortunately this is a common problem!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.