Distance between inlet and exhaust of MVHR

[Adsibob]

MVHR unit being installed tomorrow. The original design of the inlet and exhaust was as follows:

• exhaust was very close, about 20cm below the roofline, though not the ridge of roof as the MVHR is towards the front of the house and the  as the pitch of roof is 45 degrees, the ridge of the roof is about 2m higher up than that
• inlet was 1m directly below the exhaust.

I pointed out to the company designing and installing the MVHR system that they could move the inlet 1m to the left so that it would also be closer to the roofline and increase the distance between inlet and exhaust from 1m to 1.414m (imagine a right angle triangle where two sides are 1m each and the hypotenuse is 1.414m). This, I thought would be better for avoiding contamination of fresh air with the exhaust, as the inlet would also be closer the roofline and so have better access to the fresh air above the roof, rather than being constrained to the passageway between my house and the neighbour's house. The company agreed.

 

However, they have now said there isn't really space to do it this way and have drilled the holes in the brick wall as originally designed, i.e. one hole directly above the other with only 1m distance between the two. As the exhaust air will probably always be very fractionally warmed than the fresh air (because no heat exchanger is 100% efficient), the exhaust air should rise upon exiting the house, which should hopefully mean I am worrying about nothing in terms of cross contamination. Or am I? 1m just doesn't seem sufficient in my view.

 

[mike2016]

It's normally 1.5m - 2m on a horizontal plane. That's so wind blowing one particular direction won't foul the intake. Vertically you've sited the intel below the exhaust which is good. You can get a combined terminal worst case so you're already ahead of the game there with 1m separation!

 

There are some other threads worth reading on this topic on this site - see below:

 

 

[tonyshouse]

I think that in practice it will be ok , there will be plenty of air moving.