Balancing radiators

[Rick Hughes]

No problem .. .things evolve, I wrote it about 10 years ago.

[Phil Addison]

Yes

Dunno... probably. White spirit should clean up any goo.

It's still on, waiting for that final tweak when I get the round tuits.

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me

[Phil Addison]

Hi Rick, glad to see your still keeping an eye on us :-). The current piece is in need of an overhaul too, in the light of current queries. Any comments/suggestions welcome, and in any case I will re-read yours to check if there is anything to be added.

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me

[Peter]

I'm being dim, but I can't see the point of balancing radiators that are fitted with TRVs?

Sure, you can run the whole system flat out with the TRVs open, but surely as soon as they cut in the system will go out of balance and undo all ones hard work?

Peter

[Set Square]

If you *don't* balance such a system, the rads with the highest flow rate will heat up first - and only when their TRVs close will the other rads see any heat. Is this what you want?

[Phil Addison]

Balance is the word causing trouble here and it may not be the best choice, but we are stuck with it.

The objective of balancing is to restrict flow in the radiator pipework such that no radiator takes an excessive flow. If that was not done, the radiators on more restricted flows would be starved and not get properly hot.

If the system is correctly designed the pump will be just powerful enough for the most restricted radiator (usually the one on the longest run) to get sufficient water to fully heat it when its valves are fully open. However, if a radiator closer to the boiler has its valves fully open, it will allow loads of water through itself, bypassing the more restricted distant one. The effect of this extra flow is to reduce the pump pressure that is available to push the water to the furthest radiator, which will then fail to heat properly.

The solution is to restrict the nearer one, and also the intermediate ones, so that they only takes the water needed. That way a high pump pressure is maintained and each radiator gets only its proper share, and the system is said to be balanced.

You ask what happens if a TRV now starts to close down? The answer is that the TRV radiator just takes less water. Because the pump pressure is nearly equally applied to all radiators, the others are unaffected. Actually the pump pressure will rise slightly due to the reduced total flow, and this will push a very small extra amount equally through the remaining radiators.

Another way of looking at this is to consider what happens when one radiator TRV closes down. Once it is closed completely the system just becomes a system with one less radiator, the remaining ones still being in balance with each other.

As you extend this process to all the TRVs closing down we find that the water flow through the radiator circuits is much (or completely) reduced. This will cause the pump pressure to rise to its maximum value, and it is this higher pressure that can open an automatic bypass valve (if fitted) to maintain a minimal flow through the boiler.

Phil The uk.d-i-y FAQ is at

NOSPAM from address to email me