MVHR inlet and Exhaust pipe diameter?

[BotusBuild]

In need of a sanity check/advice please ...

Previously I have seen 150mm as the diameter for inlet and exhaust pipes for an MVHR unit. I haven't yet got a final design or spec for the system we will install, but want to leave some suitable holes in the ICF wall when it is poured. My thinking is to leave a pair of 200mm diameter holes to be on the safe side as I can't imagine needing anything bigger.

 

Brief build info if it helps - the finished floor area will be approx 260 sq m, 3 bed, 2 bathroom, open plan kitchen/dining/lounge, entrance hall, hall and stairs, Workroom, Store room

[JohnMo]

You need reduce your pressure drops to/ from the outside world, so the size will depend on the length, number of bends and flow rate. 

 

As you say for now 200mm would be ok.  I inserted plastic tube through the ICF, leaving an overhang either side of the wall and foamed into place and when I did the concrete pour the concrete just formed around it.

[Iceverge]

I would consider casting the pipes into the ICF from day 1 with a slight slope to the outside for condensation. 

 

You're about at the threshold (260m2) for units moving from 150/160mm ducting to 180/200mm so I would use the larger ducts. 

 

[Thorfun]

our MVHR outlets are 250mm reducing down to 200mm pipework internally. just fyi. but we have a larger house with 90mm semi-rigid ducting so I guess we need to bring in more air.