Balancing radiators - more details pls Felix!

Hi Felix

On an earlier post you gave details of how to balance the radiators.

Just wanted to check - do you start with all the lock shields fully open (as well as the valves)?

If I follow your instructions I am going to be running up and down stairs quite a bit. Good game!

Cheers

Min

You should start with all fully open as you want to get to the least flow restriction for balance. So the ones that are the hottest and least drop you close the lockshield. When balance is achieved at least one radiator should still be fully open. That's the one or ones with the longest pipe run / most bends / smallest pipe size. That is the most flow restriction.

Thanks Malc.
I'll give it a go.
Min

Malc is spot on but I've just thought of another approach which might be quicker, based on the fact that radiators heat up a lot faster than they cool down.

With all valves open, rank your radiators as best you can in temperature order. Remember this order. Now close the lockshields of all radiators except the coldest and have a long tea break while they all cool down. The original coldest radiator should now be very hot. Open the lockshield on the (original) second coldest until it matches the first one. When you're happy that both are equally hot, move on to the third coldest and so on.

Ingenious, thanks. I'll let you know if it works.

Think I'll get a thermomenter to make it easier. Any suggestions of what sort??

Just remembered, I fitted a TRV to the return side of one radiator.
Does it matter that the lock shield is on the return?

Thanks

It doesn't matter whether the lockshield valve is in the flow or return but some TRV's do care. If you ever hear a sound like a foghorn echoing around your pipes check that valve. What happens is that at some point of its travel, the valve begins to act like a reed in a wind instrument. A slight shift in valve setting will stop the noise but it's likely to recur at a different room temperature. Let's hope you don't have this problem.

I can't recommend any specific thermometer because I don't have one but the easiest kind to use has a probe and a little digital display. The important detail is that it must be TIP SENSITIVE. This means that it measures only at the probe tip and does not take an average along the probe length. To use it you simply hold the tip against the pipe, preferably with a dab of grease to improve thermal contact.

You'll notice that I said pipe. What you really want to measure here is the difference in temperature between the flow and return pipes. You want all your radiators to show the same temperature drop.

What you need most, whether you use you hand or a thermometer, is a lot of patience. When you have a radiator full of water and you can't expect it's temperature to change as soon as you move a valve. You have to make a small adjustment and then wait, and wait, and wait ---

Maplin had an offer on their IR thermostat a while ago. Might be still on. IR is probably the easiest. Zap and you have it. But, I find IR does not read round pipes or shiny surfaces that well so I use the bottom corners on the rad (flat and white) to read my in/out temperatures.

I was doing a set of readings when the CH kicked in for evening time. You need to wait until the radiators are fairly warm, say >75% towards final temperature. Then get the readings done before the room thermostat turns off the CH. Then work out the drops across each radiator and tweak the lockshields ready for the next test. Repeat next day and so on. That way it takes about 15mins a day and about a week to get balance. Which is better than waiting for the system to stabilize after you make a change. Given the thermal inertia in CH you'd want to allow at least a hour to see the effect of any changes.

The actual drop across the rads is not important to start with. Just get them all the same. After that you can change the pump speed to get the 11C across the boiler, or more if it is a condenser.

thermal inertia ohhhhh
been reading the books malc

Malc - Bsc(Hons) CEng MIEE MIRSE So excuse the habit of long words

Thanks Felix and Malc for fab advice. Now know exactly what I'm doing and 15 mins a day fits my boredom threshold. Who wants to spend the weekend waiting for radaitors to cool down!

Happy with long words: thermal inertia is perfect description. Also useful to hear about tip thermometers.

Cheers
Min