MVHR balancing - unsure if done correctly?

[Oz07]

I have recently used a contractor to balance a MVHR system and am not entirely convinced it has been done correctly. I am happy to be proved wrong so if anyone could point to any resources which show I am mistaken I will be just as happy as if the opposite is true?

 

So firstly they came out to balance the system. A certificate was sent out with the wrong floor area and missing a supply terminal in the figures. I contacted contractor and they said would sort. New certificate comes out with right floor area and 3rd bedroom supply added on. I have a few issues.

 

The measured airflow on the supply side is higher on low setting than on boost on the initial cert, and dead level on the updated one. Considering the fan speeds on boost are at 50 something % compared to 30 something % on low I find this unlikely?

 

On the initial cert the total of the supply figures was pretty much level with the total of the extract, within .1 l/s. The new cert shows the new room added onto the supply side but now the total l/s of these figures is out by over 10% compared to extract.

 

The property has 3 bedrooms so it doesn't seem to comply with the building regs doc F Table 1.3. Overall i'm not too precious about this as I think the minimum rates have been achieved on wet rooms and kitchens.

 

I am suspicious that on the initial certificate despite missing a supply terminal the overall supply and extract figures were balanced to within .1l/s and on the new certificate they are out. I have contacted contractor and he is insistent the supply & extract figures don't have to match up for the system to be balanced. He says it complies with building regs which I don't doubt (ish, excluding table 1.3) but when I engaged it was for the system to be balanced.

 

Initial cert

 

Updated Cert

Edited June 10, 2023 by Oz07

[Oz07]

No reply here but just for closure the invoice was cancelled, apparently the certificate was "cancelled" too. No way was i trusting those figures everything was a bit fishy for my liking.