I used 8 lengths of 22mm,gas took 3 lengths,flow and return 5 ,from boiler to tees that split to feed 3 rads and 4 rads ran 22m ,tee for rad,tee for drops then 15mm ,then the back 3 rad,drops,then 15 mm,so now clock with boiler ,loop with boiler,inhibator £9 quid,roomstat £15 quid so another...