This is a little case study review of a Nuaire Drimaster positive input ventilation system, why it didn’t work and there continued to be a condensation and mould problem.

First of all I was told the surveyor that came out to offer a free ventilation survey used a hygrometer to determine the relative humidity levels in the property. This is fine if all you want is a snap shot survey, which in fairness most of these surveys are, but it would be more appropriate in my opinion to carry this type of survey out first thing in the morning when there is more likely to be more water vapour in the property from sleeping with closed bedroom doors and windows etc, this will give you a more realistic snap shot in time survey.

There was no survey of the building externally looking for any obvious defects like penetrating damp from defective guttering etc, simple things like this could be making the wall colder and it is more likely to cause a mould, condensation or even the mis-diagnosis of rising dampness.

I was told there was no inspection of the building internally either, it is imperative to measure extraction rates for the bathroom and kitchen fans if there is any…….How can you tell if the fan is working as designed?

What they missed, well where do we start, first of all the most obvious problem was the ducting for the tumble drier. This was literally pumping out moisture when I carried out my survey, so this should be the first thing that is fixed to eliminate moisture.


The below picture shows when it becomes a serious issue, this isn’t poor diagnosis or trying to flog a fan. As you can see the diffuser for the Nuaire Drimaster positive input ventilation system is very close to the smoke alarm, this should be a minimum of 1 meter away unless there is a blanking strip installed to prevent air blowing across the smoke alarm to ensure it actually works if there is a fire. Another really serious matter is the artex, any house built before 2000 could have asbestos, and it is well documented that artex could have asbestos in it. Before any works are carried out it is necessary to have the artex tested for asbestos. Also note the spot lights, it is also well known if these are not sealed how can this system work as it can’t really positively charge the house because of the air leakage into the roof…….


There was no undercut under the doors to allow good air transfer through the building, the doors were dragging across the new carpet, there should be around 10mm.


The roof is supposed to be well ventilated, this will ensure drier external air is drawn into the roof. This one had no roof vents, soffit vents and this is why the rafters were damp and the gable wall was below dew point, which is clear in the above isotherm using thermal imaging.


Condensation was running down the roofing felt during the survey.


This homeowner purchased a cheap Nuaire Drimaster off the internet and actually paid a so called specialist in these systems to fit it and has put his family at risk if there is a fire, and also put them at risk of asbestos, the worst thing of all he paid for that service.

If you need a positive input ventilation system installed correctly along with a detailed survey using thermal imaging by a qualified BPEC Domestic Ventilation System surveyor, and a damp specialist contact us,  we will be pleased to offer our services.

If we don’t cover your area then there is a BPEC Qualification on Domestic Ventilation Systems that is definitely a must,  you should check an installer has this, and also sufficient experience with damp diagnosis and surveying.

Ventilation can be checked quickly using a calibrated anemometer.


You may also want to read about another case study using data logging to show that the ventilation wasn’t installed correctly, and was causing condensation that was mis-diagnosed as either a leak or rising damp. Using data loggers to produce graphs shows exactly what is going on….data is king!



Posted by Complete Preservation

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