Discuss Low loss header in a central heating system in the Water Underfloor Heating Advice area at Plumbers Forums


Gas Engineer
This is our heating system that was originally installed to support a GSHP. The GSHP has since been replaced with a gas boiler but the UFH has never worked satisfactorily. My plan is to install a Low loss header in the system where shown on the sketch. Will this work?
Is the boiler a heat only boiler with the circ pump pumping into the boiler return?
Has each UFH got a mixing valve (TMV) and a manifold pump?
Do you want to have the cylinder heating on at the same time as the UFH?
Hi John, thanks for your reply
The boiler is a Worcester System boiler so has its own pump. Each manifold also has its own pump but as they were originally paired to a GSHP there is no TMV as the water from the GSHP was generally cool enough for the UFH circuit. The cylinder is “always on” and controlled by a cylinder stat.
A low loss header, from what I’ve read about them, seems to be the perfect solution for this situation but of course I’m always willing to be pointed down the road of righteousness!
Depends on boiler output and the output of each UFH system and if you plan to run them all together.
On your system if the boiler output is sized to the total UFH+cylinder demand, then assuming that the boiler flowtemp is set to the UFH flowtemp requirement and assuming a manifold dT of 10C and the same for the cylinder coil then you won't be able to run them all together because the max boiler heat exchanger loss is based on a dT of 20C, so the boiler circ pump would require 4 times the head. A typical UFH system with a TMV and manifold pump will only send a max of ~ 45% of the UFH circ flow back to the boiler even allowing for some boiler by pass to increase the return temp so it would run with a UFH dT of say 10C and a boiler dT of ~ 15C and even with the HW heating on shouldn't exceed the max flowrate.
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