Piping

[Sam Wardill]

I have a system where the rads at the end of the circuit do not heat up at all unless all other rads are turned off. The system has never been balanced since the new boiler plus new rads were installed. Obviously balancing should help. However I wonder if the plumbing is adequate. The main flow and return is 22mm pipe and this tees and reduces to 15mm x 15mm to feed one rad. The other 15mm pipe goes on to feed 3 further rads (with 15mm tees). It used to only feed 2 rads and a 3rd one has been added recently.

Is it OK to feed 3 rads from a 15mm pipe in this manner when the main flow and return are 22mm?

 

[oz-plumber]

It depends on the kW output of each radiator, the kW output of the rest of the system on 22mm pipe, the boiler size and the pump capacity and pump head.
It may be a case of balancing the system, as you state, but then again it may not.

 

[Sam Wardill]

It depends on the kW output of each radiator, the kW output of the rest of the system on 22mm pipe, the boiler size and the pump capacity and pump head.
It may be a case of balancing the system, as you state, but then again it may not.

Is there a way to calculate or is it just necessary to do by trial and error?

 

[glenno1]

Try turning radiators lockshield valves off and then 1/4 turn back on

 

[oz-plumber]

There are very definitive way of working out pipe sizing and flow rates to radiators.
Trial and error should not be part of this.

As stated, kW output of all radiators, length of main run from boiler ( longest run - index circuit )
Head capacity of pump.
All these factors are required to determine correct pipe size and flow rate required.

Then again, spend time balancing the system and it may solve the problem.

 

[stevetheplumber]

if you need to do calcs for normal domestic work youve not been doing it long enough