CH balancing

Hi,

I printed out the page from the faq but I'm getting really fed-up with trying to balance these radiators!

I bought an IR thermometer. I'm holding it close to the pipe to get a narrow beam but even so, just a slight movement gives a temperature drop of 10C. I put masking tape on the pipes. Is this causing some of the problem? Should I be using insulating tape instead?

Should I start with the lockshields where they are and tweak or should I start with them all open?

Do you make changes to several radiators at the end of each run or just one radiator per run? Or do you tweak as you go along?

How long should I wait for things to stabilise before re-measuring?

Thanks.

Reply to
Fred
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I use little squares of black tape on a flat surface of the radiators - just inboard of the valve connections.

If the system has previously been balanced, and is in a *reasonable* state of balance, start with them where they are. Otherwise start with them fully open.

2 or 3 at the most. Turn down the ones with the smallest temperature differential.

Probably about 10 minutes - but you need to make sure that the system is running the whole time - so turn any room stats up to max, and open some windows if necessary.

Reply to
Roger Mills

Thanks. I'll give that a try.

I think the FAQ advises 1/4 turn adjustments. I thought that valves like lock shields are non-linear. Does this mean that the first few turns will make no difference and then near the end, the slightest turn will make a difference? Should I use turns smaller than 1/4 to fine tune?

I've got an assortment of radiators all with different lock shields so each radiator requires a different spanner to adjust the lock shield! (I can't use the cap off the other valve as these have been replaced with TRVS).

I'm having most problems with the towel radiator in the bathroom. It's scalding hot to touch but not showing much of a temperature drop. Should the drop across a towel radiator be the same as the "conventional" radiators?

How accurate should I be in matching temperature drops. Should I try to get each rad. to have a drop of say 10C, or does it matter if one has 8C, another 12C, another 9C, etc?

Daft question: does the boiler need to be firing? Or as long as the pump is circulating hot water is that enough?

Thanks again.

Reply to
Fred

It's certainly non-linear, and most of the action occurs when it's getting on for closed, so you can certainly turn it down quite a lot - maybe half-way - to start with. The rest is really 'suck it and see'!

Towel radiators are a waste of time as space heaters anyway, but you'll get a *bit* more out of one by running it at a higher average temperature - i.e. with a smaller drop. But don't go below (say) 5 or 6 degrees, or you'll be at risk of starving the other radiators.

It's not an exact science - and you'll never get then all exactly equal. Variations of a couple of degrees don't really matter. What you are trying to avoid is having some with a 2 degree drop and others with 20 degrees or more - which is probably what you'll have at the beginning.

Ideally the boiler *should* be firing but that is virtually impossible to achieve. Unless the system is dissipating the full output of the boiler, it will inevitably cut in and out on its own thermostat. But that at least means that the water being circulated is at a more or less constant temperature - within the hysteresis of the boiler's stat. Don't forget that you're measuring the *difference* across each rad, so if the flow temperature varies slightly, it's not a disaster. It *is*, of course, vital to keep the pump running - by turning up the room stat and, if necessary, opening a few windows to stop the house getting too hot - although that shouldn't be necessary this time of year!

Reply to
Roger Mills

The message from Fred contains these words:

I have not had any direct experience of towel radiators but as towel radiators typically have a much smaller surface area than even a small conventional radiator it may be difficult to find a point between little temperature drop and practically off.

The object of the exercise is to get the specific heat output of each radiator to match but I wouldn't have thought at a 10% variation (or perhaps even more) in temperature drop would be a problem and I suspect that getting any closer would probably be an illusion. The larger the radiator the larger the flow through the radiator for the same temperature drop which is why you may have trouble adjusting a dinky towel rail.

Hobsons choice (unless you have a sophisticated modulating boiler). If the boiler is firing the circulating water is being heated and the flow temperature continuously rising and if the pump is on over run the circulating water is being cooled. I think what you must avoid is the warm-up phase below normal operating temperatures, any period during which the water isn't circulating and any period shortly thereafter. If the pump is running and the flow temperature is high enough you will then only have the problem of finding a period when the inlet and outlet temperatures of a particular radiator aren't varying fast enough to invalidate your results.

It may be that it doesn't matter that you are getting a higher (or lower) than true temperature drop across a radiator provided you consistently opt for the firing or the over run phase or it might be better if you take measurements from both phases and average. If my central heating system is any guide I think you may have some difficulty in finding any period where both inlet and outlet temperatures of a radiator are stable.

Reply to
Roger

But the same would be true for most CH systems, so what do people do?

Reply to
Fred

I balance systems so each radiator feels equally hot. Since I'm doing this for a living (i.e. people are paying me to do it) I don't have time (i.e. I don't charge them) for spending ages getting everything right by the book. If it feels right to me and to them and everything's nice & warm & toasty everyone's happy.

As for 'by the book' there's a lot said about getting temperature

*drops* across rads the same. However a radiator's heat output is a function of its mean temperature, and it is this which we want to equalise. Since the flow resistances of the pipework feeding each rad is probably different (and/or these flow resistances are not in proportion to the rads' own flow resistances) then getting the temperature drop across each rad the same should ensure that each rad is operating at the same mean temperature. In other words balancing temperature drops are a means to the end of equalising rads' mean surface temperatures.

IMHO, E&OE, YMMV, TGIF etc...

Reply to
plummer_a

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