OK I need to run a drain out of my attic to handle MVHR and maybe AC condensate / unvented HW tank tundish / water softener drain. It needs to fall about 3m and run inside about 10m of wall through a bunch of posi-joists and around a 90 bend eventually joining a 110mm toilet waste.

 

Would you run this in 28mm copper or welded 40/50mm PVC or, say, 28mm Hep20? If not all copper, would the first bit from the tundish need to be copper and for how far?

 

What would you do?

Edited May 31May 31 by Alan Ambrose

110mm for all the runs through the posi-joists, and if possible run that all the way to the plant room. 
 

If that's too big for the final vertical rinse, reduce to 50mm as late as you can.

 

The 3m drop means you’ll need an AAV in the room, a min of 600mm higher than the highest wet entry into the pipe run.

 

Does this drop down near a bedroom? 

Regs are pretty strict about tundish discharge. 

You definitely can't run in hep2o or similar and I think your tank size limits whether you can discharge into soil stack.

We ended up with 35mm copper for a similar length run as you have to size up depending on length and the number of bends

45 minutes ago, torre said:

Regs are pretty strict about tundish discharge. 

You definitely can't run in hep2o or similar and I think your tank size limits whether you can discharge into soil stack.

We ended up with 35mm copper for a similar length run as you have to size up depending on length and the number of bends

As long as you can show its high temp rated plastic, you can avoid copper. Most modern plastics are suitable, but you need to confirm.

 

35 & 42mm copper pipe and fittings are hideously expensive.  

OK many thanks for those thoughts. I see the Hotun tundish guys re pipework say:

 

"Polypropylene (PP), Modified Plasticized Polyvinyl Chloride (MuPVC) or High-Density Poly Ethylene (HDPE) are all acceptable materials."

 

So, I'm leaning towards one of those, probably in 40 or 50mm as the tank I'm looking at has 1" BSP connections (i.e. ~31mm ID) and a long run so suggests I need to go 2 sizes up. Also a waterless trap.