Thoughts on my plans very much appreciated

[cjc88]

I started a DIY MVHR build as I wanted to make my house a bit more insulated, but already have condensation on windows and smells that linger for says, so it seemed like a sensible next step.

 

My attic is cold, but the only place I really have space for a unit, and figured I could insulate the chimneys at the same time as passing MVHR pipes down them (after putting in a lintel) - 3 chimneys front and 3 at the back for a 3 story mid-terrace house of ~140sqm. The chimneys are pretty warm now I have insulated them at the attic (no external walls), and added small breather vents into the house. I have mostly insulated the ducting in the chimney and will of course do the same in the attic once I have finalised manifold locations, and probably the MVHR itself given it's a cold attic.

 

There are some rooms I still need to work out the semi-rigid duct path (no chimney to use for several rooms), but Im starting to think about next steps and would love to hear your thoughts/concerns please?

 

1. Im planning to put the MVHR in the middle of the chimneys, and the semi-rigid ducting can all meet at some manifolds there quite easily. Do you think it would be best to wall mount with some brackets, or just put some wooden joists to support its base?
2. If I put the external vents through the chimney then there will be a lot of bends to deal with (around the roof supports and going down to the opening for the chimney before going up the chimney to some form of cowl). Would I need a drain point at the bottom of this ductwork, or is it generally ok so long as the ductwork is insulated?
3. My alternative is to ask a roofer to cut a hole in my roof and put the external vents directly above the MVHR (and could then totally remove chimney at some point - given I think I can see water marks on the chimney above the lintel it presumably needs some work anyway). Is this worthwhile do you think? (shorter pipework but more invasive and risky to interfere with the roof, given somebody in the past made the strange decision to add planks added on the back of the roof)
4. A Zehnder Q350 is an impossible squeeze through my roof hatch at present, but I may cut the hatch just to allow entry and then re-seal... Though definite effort! Alternative options with a width <510mm seem to sacrifice a fair bit.
5. The Zehnder needs 160mm vents, but if I used 200mm vents could I use flexi pipework to make the routing easier (due to the above), or would I need more like 250mm to compensate for all the ridges....? (the chimneys are about 240mm wide, but quite sooty, so definitely needs lining)

 

Any thoughts or feedback very much welcome, thanks in advance!

 

 

Edited 2 hours ago by cjc88