Drain off valve for trunk & branch

[Deleted member 220192]

Recently installed new heating system in a house I've got.

Ripped out all the old copper and started fresh.

Installed new copper according to the trunk and branch design, flow begins 22, then splits to 2 x 15, one 15 feeds upstairs rads, one does downstairs.

Return is exactly the same.

My question is this though, As well as downstairs rads each having DOV locksheilds for part draining etc, I also want to be able to drain every drop so want to place a DOV on the lowest part of the system under floor, so do I solder a pipe at lowest point between flow & return and attach DOV there? This would need an isolator too wouldnt it?

Actually might have just answered my own question already, since flow and return are linked by rads, a DOV on either pipe at lowest point would do the job right? My original thinking was flawed as I dont have any rads as yet.

 

[PrenticeBoyofDerry]

Firstly it would be wise to actually calculate your pipe sizing according to rad size, pipe distances and resistance, rather than taking it for granted that taking 15mm from 22mm for both upstairs and downstairs is suitable.
With regards to drain off, lowest part of each drop, whether that be flow or return, but not both if the pipe/drain off is below the rad.

 

[Deleted member 220192]

Its a 2 up 2 down terrace! 5 rads in total, resistance should be low as I've made all my own bends rather than 90 degree E/F etc.... combi in loft.

So one DOV under floor at lowest point in pipe either flow or return

 

[PrenticeBoyofDerry]

At lowest point in an accessible location, if both F&R are under floor and below rad, they will both require drain offs to fully drain down all pipework, if you have tails rising to each rad valve then you would still require both F&R drain offs to completely drain pipework, it will all depend how the pipes are installed.

 

[Deleted member 220192]

Ive run the flow to the left side of every rad, return to the right.. other than the rads, there is no other connections between f+r