Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications:: Apply now.
They will be able to show you any leakage paths by localised smoke testing once the house is under pressure. The test result will be expressed as M3/hr/M2@50pa which is cubic metres per hour measured against the envelope area of the building at 50 pascals pressure. They should also be able to tell you the ACH, air changes per hour, which is measured against the volume of the building. For MVHR to work efficiently the air leakage needs to be very low preferably no more than 1-2 M3/hr/M2@50pa. I believe BSRIA have test engineers around the country.
Most sub contractors even from good sources will likely be in a hurry, and keen to get away to his next job and not fiddle about, you can pay extra for leak finding time though, probably in the small print
you could do better to find your own local tester and ideally a nice one who will assist you tracking leaks and do as a part of the job
MHRV will probably work OK if you are installing a joined up barrier
I used Stroma, they helpfully called around a couple of months before the test with advice (the guy was local to us). When they did the test they lent me a smoke puffer so I could go around the house while it was pressurised/depressurised and find the leaks myself. I probably should have paid to have a bit longer but I was able to fix a few obvious things and reduce the final recorded airtighness score to well below our targe. Cost similar to arnyj's BSRIA.