Are the building regs requirements for ventilation in an air tight build a bit bonkers or have I got a problem with my MVHR system? Finally got the dust under control enough to try commissioning the MVHR system in my new build. Plumber hired a calibarted and certified anemometer and off we went.... System is a Polypipe Silavent HRX2 with semi ridgid ducting in a radial layout (designed by Polypipe based on the house plans, or at least they said it met the demand).
Part F requires based on floor area at least 0.3 x 217 = 65 l/s flow, we divided this based on room volume between kitchen, bathroom and shower room, opened the vents and cranked up the fan to deliver sufficient flow at the "limiting terminus" the bathroom farthest from the unit. Ran around adjusting the vents to get the proportioned balanced flow rates (totaling 65l/s extract and 65l/s supply) for each room. That was fine but it is incredibly noisey at that level, the house was thrubbing! No way would we be happy living with this on continually, it was also drafty anywhere near a vent. Of course we have turned it down to a quietly comfortable level, but what gives, are we going to have problems - stuffiness, condensation etc. - if we don't live with the required minimum 65l/s flow?
If the reg values are sensible then is the fan noisy because it is under powered for length of ducting and volume of house it is serving? How do I find out and what can I do now?
I am hoping it is venitlation over kill and in reality a more gentle flow will work. We have been working here, air sealed and windows closed in the rain, and haven't noticed any lack of ventilation at all but haven't used the shower either.
Looking at volume the 65l/s flow is 234 m3/h or 0.43 ACH or 138cfm. I went seeking information from other authorities. The whole house requirements in the US are for 7.5cfm per person and 3cfm per 100 sqft. There are 2 of us hence 79.6cfm = 37.4l/s would be requred over there, a flow I can achieve without a headache. The house would need 7 people in it for the 65l/s to be necessary, yet people are complaining that these new US regs are too much!
Anyone care to share experiences with their MVHR flow settings.