How bad is this cock-up ?

[pstunt]

We are about a month away from completing our build, a conversion of a an old stable. We have fitted all the ducting and about to order the 2 MVHR units having had the parts and the vent locations planned by BPC Ventilation about two years ago.

 

The issue is neither my builder or myself noticed that the living areas and bathroom required two duct runs not one, which is what we fitted. Yes, this is a major cock up but how bad is this oversight likely to be ? 

 

My guess is that it will still work but more energy will be required and the risk of more noise / vibration ? 

 

I should say that even if we had realised from the off we would never have been able to accommodate dual ducting, as it is a conversion and roof space was very limited. MVHR was never a must have for us but more a nice to have but I would be very disappointed if it' wont work anywhere near it should be.  We were never aiming for passive house airtightness standard but have been reasonably conscientious along the way. e.g. Filling service holes in membranes and not window trickle vents.  

[JohnMo]

What size duct are you using?

[LA3222]

It will be fine. When the dude commissioned my self installed MVHR (due to BC moaning) he set the flows to nearly 50%. I throttled it down to 30% and no issues with humidity etc. I'm sure that one pupe will provide enough airflow to clear out the stale air. Not sure anyone on here runs theirs at design flow rates so conversely having one pipe vs two will yield a similar result but may need to run yours closer to design flow rate.

[pstunt]

10 minutes ago, JohnMo said:

What size duct are you using?

75 mm radial 

[pstunt]

8 minutes ago, LA3222 said:

It will be fine. When the dude commissioned my self installed MVHR (due to BC moaning) he set the flows to nearly 50%. I throttled it down to 30% and no issues with humidity etc. I'm sure that one pupe will provide enough airflow to clear out the stale air. Not sure anyone on here runs theirs at design flow rates so conversely having one pipe vs two will yield a similar result but may need to run yours closer to design flow rate.

Thanks for this. I do hope you  are right but I guess there not much I can do about it anyway.

[joe90]

Mine is 75 radial and only one feed to all area,s, many tales here of MVHR being run at lower rates than theoretical ones so I recon you will be alright 👍

[JonBATConsult]

That really is a right old Cock up isnt it. Without figures I cant help you but normally. I would not expect to see more than 8l/s being force down a 75mm duct. One problem is you will end up with a large oressure drop on your grille and it will regenerate noise.. Reducing your your fan duty below what has been advised is not reccomended and woudnt comply with part F. If you have go to the effor of sealing up its important to follow through with the correct MVHR setup. 

 

(15 years working in building acoustics and air permeability)