CH Layout questions

[c0wb0y]

Right folks, so - I'll be laying easy-lay PB pipe in a 3-bed semi for a Central Heating install and had some questions:

1) The 22mm Flow/Return runs are beneath floorboards - how close should I get to the radiators before reducing and 'tailing-off' in 15mm copper? I've seen plumbers run 22mm pipe to just beneath the rads and only breach floorboards in copper for the visible sections. But then some plumbers say the reducing should take place a good meter or so away from the rads. Thoughts, please?

2) If possible, I want to keep the entire CH install in 22mm using the fewest push-fit joints (I'm trying to avoid having to buy a 15mm coil). I can knock-up several tails by soldering 15mm to 22mm with offcuts/spare copper lengths I have (just need to buy end-feed reducers). Does this sound about right and if so, should I solder drain-off valves onto the tails or buy those chrome valves with drain-offs built on?

3) Does every single radiator in the house need a drain-off valve - including the upstairs ones?

4) Similar to Q1 above: how near to the combi boiler should I come with the flow/return before leaving it for the plumber to arrive? I know boilers need the 'beginning bit' in copper: would approx 1 meter suffice? Or is there a minimum requirement?

Cheers

 

[c0wb0y]

bump

 

[oldbutnotdead]

There's a minimum 1 metre copper from the boiler, i assume thats tube length rather than distance but check.
If your pipework is underfloor with upstands to the rads there's no real point having draincocks everywhere. The chrome valves with draincock are ok for the hall or the kitchen, bit ugly for the sitting room.
Pipe sizing has 3 main determinants- how much heat, how far, how many bends (the latter 2 for headloss calcs). Unless you have monster rads, up to 3m of 15mm will be fine, 200mm will also be fine so link to your 22 where you can get to the couplers if you need to.