Balancing rads

Kashkai

My radiators are either scalding or stone cold so they need balancing. I went round the house last night after I turned the heating on and checked which pipes heated up first to see which were the flow and which were the return pipes. I bought a digital thermometre to measure the temperature difference between the two pipes which should be 10-12 degrees (correct?). However, I'm having trouble deciding which rad I should start with as my house is an old bungalow with three large extensions on it so its hard to know which is the closest rad to the burner, i.e. the rads in the end bedroom that are adjacent to the outside burner actually heat up last.

Can someone give me a guide to balancing the rads: i.e.

1. Assist in finding what order I should balance them in
2. Do I need to turn the burner's stat all the way up for this test?
3. Do I open the flow valve all the way on all rads
4. Do I open or even touch the return valves prior to balancing or just leave them as is?
5. If I find the first rad in the system, do I turn teh return valve all the way down or open it up all the way at the start of the balancing?

Thanks

Pete67

I think you'll find everyone has their own method of balancing a system. Heres mine:

1) Identify flow and return on each radiator, (flow heats up first, or is hotter of the two pipes if rad is already hot).

2) Boiler thermostat set at 75 to 80C, vent all radiators to remove any air, and ensure system pressure is correct, approx 1 bar cold at the boiler for a sealed system.

3) Open all hand valves fully on the radiators, or remove the heads from TRVs so they open fully and stay that way. For a new system, set all lockshields approx 1/4 open, usually just less than one turn from closed. For an existing system leave them alone for now, unless it is obvious that the system is completely unbalanced, in which case adjust as for a new system.

4) ensure any zone valves are open (turn room thermostats up to max or use override on the zone valve)

5) Switch on heating and wait 20 to 30 minutes for all the rads to heat up.

6) Measure the flow and return temp at each radiator and write them down.

7) For radiators with temp drop of less than 12 degrees close the lockshield valve slightly.

8) If the temp drop is more than 12 degees open the lockshield valve slightly.

9) Wait a short while after each set of adjustments before checking the temperatures again.

Repeat step 6 to 9 until all rads have approx 12 degrees drop from flow to return.

Pay attention to the larger radiators first, and leave the very small ones to last, it may be difficult to get a 12 degree drop on very small radiators anyway so a bit less is fine.


Once done, replace TRV heads if applicable, put covers back on the lockshields and reset room thermostats and/or zone valves to normal.

Note, if you have a condensing boiler the average return temperature needs to be below 60C, ideally 55C for maximum efficiency so you should adjust lockshields to give a 20C temp drop at the radiators. However unless the radiators were sized for a 20C drop you may then find that the rooms are not heated to acceptable comfort levels in very cold weather. You might have to compromise a bit between comfort and efficiency.


If you can't achieve the required temperatures then there may be other issues at play, especially on an older system. For example, sludge build up in radiators, or even poor system design, poor piping layout or pipesizing, undersized boiler, pump etc etc.

Hope this helps.

Kashkai

Thanks a lot Pete. Much appreciated.

Forgot to ask what temperature should I be looking for from the flow pipe? My Firebird 150 oil burner is not a condensing model and the stat on it is marked in hatch lines of increasing size, not numerical. It is currently set on the third largest hatch line from maximum.

Pete67

I normally set the boiler to max prior to starting balancing, you can check the actual temp with a digital thermometer once the boiler has been running for a while and the burner is cycling on and off. It should be somewhere around 85C.

johneym

hi Pete,

what are lockshields please? I have new pliumbing done in an old house. No trv or thermoststs etc.

Thanks a lot,

John

Buford T Justice

You have two valves on each rad in the house,

One is the regular valve, if you don't have a TRV, ( with the adjustable handle) and the other is the lockshield valve, which needs to be adjusted by a wrench.

johneym

thanks fingers