Hi guys. I am putting in 2 altherma heating system into a house. We need 5 pipes from the plantroom to the house however the plumber has only put in 4 pipes. Would it be possible to have a common return off the upstairs and downstairs systems returning to 2 low loss headers in the plantroom. The pipes are already underground so what I'm ask8ng basically, can 2 separate 22mm returns tee into 1 22mm return and still flow back to the low loss headers at the same rate they are being pumped out at??many thanks rob.