Blocking MVHR for an Air Tightness Test

[cswd]

We've just finished a fairly extensive retrofit (MVHR, ASHP, EWI, triple glazing etc) and had a final air tightness test. I was getting different advice from various locations about what to do with the MVHR when carrying out an air tightness test so, for reference, here's what Zehnder told me to do with our Zehnder Q450 ComfoAir:

'I can confirm you will need to block up the intake and exhaust, so cover the terminals with a material that will block airflow.'

And in talking to them, they clarified that we were meant to block the external roof terminals.  Unfortunately, I didn't have scaffolding up anymore, so couldn't get on the roof to block them.

I hence followed the advice from the supplier (GBS) which was, roughly, 'cover the filters with plastic bags' (I used clingfilm).

 

Zehnder stated they'll look into it and update their documentation & FAQs - given you'd think pretty much anyone fitting MVHR would end up doing an air tightness test seems daft that this info is hard to find!

 

Does anyone have any better advice?

 

I'm wondering if being unable to cover the external roof vents affected our final AT test (we got 1.77).

Thanks,

Stuart

 

[JohnMo]

MVHR units themselves leak, we had a similar issue, we blocked the inside room terminals, but I could feel the air leaking into the room where the MVHR units are located during air test. Our final air test was no better than our pretest and all leaks during that test were fixed. If you are not passivhaus certified, the air test is just a piece of paper to keep building control happy.

[Blooda]

We blocked the inside terminals for the Air test.

 

Took the White Covers off - Stuffed car sponges in [in plastic bag] and then sealed with 150mm Silver Foil Tape, cut into nice semicircle.  In hind sight the sponges were not needed, but it was fun going into B&M and buying 24 sponges

Remember to switch it off.

 

 

 

 

 

 

[Matt540]

I just disconnected the main intake and exhaust to and from the unit and taped bin bags over the ends. Seemed to do the trick 

[joth]

For our test we wrapped the intake & outlet filters in plastic bags, which seemed to do the trick. (0.5ACH on a retrofit) 

I've seen others seal the main ducts from the outside of the building ... looked like hardwork but they'd built several dozen passive houses so guess they know what works!