Rad balancing

[Tim Streater]

OK - here's this issue again :-)

Last year we had some rads replaced and the system flushed. Boiler is a Euroflame Kitchen/Utility 90/120, conventional flue, fitted about 7 years ago.

So, reading the FAQ about how to balance the system, and going back through recent threads, I've equipped myself with an IR-77L and made up a spreadsheet as advised.

Before doing this for real, I'm noting some methodology issues/questions:

1) I tried some black sticky tape on a rad, and measured about the same temp as without it (rad has white paint). From what I can read about emissivity, that's about right - or does someone have some particular tape to recommend? I do notice that a bare copper pipe reads a quite low temp.

2) Where are folks measuring the flow and return temps? On the rad itself, and if so where, or on the flow and return pipes at the point where they enter the rad? (I'd prefer the rad, it's easier to get at).

3) IIRC, the idea is to let the system come to equilibrium, and then adjust. However, with the boiler set to deliver water at 80C or so, after an hour of burning continuously, the water exiting the boiler is only at 60C. [1]

4) Some of the "distant" rads are not fully up to temp after an hour - is this reasonable? [2]

[1] Seems to me, in this case, I may as well simply adjust the boiler to produce water at 60C. [2] This is a 30s house that's been extended and with little thought apparently being given to extending the central heating in a sensible way.

[Roger Mills]

You may not notice a lot of difference, but you should get more

*consistent" readings by using black tape.

I use 1" squares (approx) of matt black duct tape, stuck onto the front surface of the radiators immediately inboard of the water connections.

Sounds like your boiler is under-powered for the job in hand. Presumably there's a constant demand for all that time, and a room stat isn't cycling on and off? [You need any room stats to be set at max throughout the balancing exercise so that the pump runs all the time and the boiler fires all the time - subject only to its own stat]

The *actual* flow temperature isn't that critical as long as it doesn't vary too much. What you're measuring is the temperature *drop* across each rad, and trying to get them all more or less equal.

No - but hopefully balancing will fix that. If that means that you have to really throttle back some of the 'warmer' radiators, you may also need to increase the pump speed.

If the flow temperature *never* reaches the boiler stat temp, then turning down the stat won't make any difference. However, it might get up higher in milder weather - or certainly in the summer when you're only heating the HW. I would be inclined to leave it as is.

This probably means that you've got several flow paths with considerably different resistances. But as long as all the rads are connected in parallel, and as long as the pump is up to it, you should still be able to balance it.

[Roger Chapman]

I had much the same issues when I checked the balance of my radiators.

I never did get very far with black tape on the inlet and outlet pipes and eventually concluded that a good enough balance could be achieved by a quick check of the temperature at the centre of each radiator (off the white paint) before the boiler switched onto a pump only phase as the temperatures of the inlet and outlet pipes never stabilised for long enough to be sure of the results.

But what is the inlet temperature? If you are expecting a 10C drop across each radiatior you shouldn't have much more than that across the boiler and with the cold weather we have been experiencing it may be that your boiler can't manage any more output. Reducing the pump speed will slow the rate of flow through the boiler so increasing the output temperature while decreasing the input temperature.

It is not perfect but given your remark below it may well not be possible to throttle down the near radiators far enough to to improve the balance without constraining the total heat output.

How do you manage for domestic hot water or is your boiler a combi? It seems to me that 60C is rather low for heating a hot water tank.

You don't say what your room temperatures have been during this exercise or how you normally control your room temperature. Both of these points may have some bearing on the outcome.

[cynic]

The thermost may "say" 80 degrees but its mass produced and no longer new! Does the flame switch on and off in response to the thermostat during the period you mention? If not what nozzle/burner pressure is the burner empoying and is the heat exchanger clean?

[Tim Streater]

By thermostat I mean the setting on the boiler. After 3 hours the water had reached 67C (as measured by my IR jobby), and if I turned the control down from its 80C setting, then between the 75C and 65C markings, the boiler went off. And on if I turned it back again.

Between 8.6 (120k Btu/h) and 9.5 bar (90k Btu/h).

Pass. The boiler is serviced twice-yearly so I shall be calling the bloke tomorrow.

[Tim Streater]

:-)

Yer not wrong there, George.

Yes, and there's more than one of them.

I don't think its a waste of time to understand how the system functions in order to reduce oil consumption. Not at today's prices. Some rads were not getting hot at all, until I noticed that after the system was flushed, the bloke had left all the LSVs completely open. So the rad and towel rail in one bathroom were a complete short circuit.

You're right that the system is crude - I count at least three control mechanisms in the system, not including the HW thermostat.

[Tim Streater]

Good point. I'll check to see if I can alter the pump speed.

Three-way valve. Hot water seems OK generally.

Well these vary. Some rads are arguably too small for their room or old (we tried to sort *that* issue last year), but there's a limit to what is possible there without starting from scratch.

At present the boiler is in a small conservatory (i.e. outside the original house footprint) and has a conventional flue using an inside chimney that dates back to prolly 1930. So if we wanted to replace it we'd have to move its location back inside so that the flue can go though a wall to the outside.

[Tim Streater]

Could be under-powered, hence why I'll be talking to the boiler man soon. The boiler doesn't go off during at least the first 90 mins its on in the evening. I know because during that time, I was out in the conservatory, where the boiler is, shoving climaflex on pipes that run from the boiler up what was the house outside wall (now inside the conservatory), where they vanish through the wall into under a bathroom floor to the airing cupboard.

I'm planning to adjust it so that the boiler is on enough to maintain the water at 65C or so. If outside temps are around 0C, then I seem to be using about 20 lt/day of oil, which seems excessive to me. My assumption here is that at present, under these conditions, it's burning a lot of oil to little effect.

Couple of related Qs:

1) When the boiler is running, is it consuming fuel and producing heat at a constant rate? No throttling up/down other that turning it on/off?

2) Is there any inefficiency (i.e., any fuel wasted), when the boiler is turned off/on frequently?

3) If the CH and HW are on together, and the HW comes up to the HW tank thermostat setting, presumably that just turns flow off to the HW tank via the 3-way valve - i.e. it doesn't turn off the boiler?

4) If my boiler actually produced water at 80C, then presumably I'd have water at 80C entering the rads and (ideally) leaving it at 70C or so?

Thanks for all replies.

[cynic]

The output is "adjusted" by selecting a nozzle size and an oil pressure. Your domestic model oil pressure will be set by the commissioning engineer having regard to the nozzle selected in accordance with the installation and service instructions. Once set it will not alter appreciably unless someone makes an alteration. You need to get hold of a radiator chart, measure up your rads and calculate the thermal load they apply to your boiler. This assumes that the radiators are sized somewhere near the needs of each room. It sounds as though there is much room for improvement

[cynic]

- Hide quoted text -

Go back to basics and start by closing in every lockshield valve to somewhere between 1/4 and 1/2 turn open. This should give you an even spread of hot water to every rad as a start. You can bugger about for days trimming after that but as others have said its a variable load and almost impossible to finish such an exercise.

[cynic]

SNIP

Correct for most domestic oil boilers

Yes - a long steady run is best but unlikely that you will be able to obtain under varying conditions

Correct as long as the rads controls are still calling for heat. Sometimes there is a brief blip in power to the boiler while the valve moves position

Pretty close give or take a degree or two drop in the pipework

[Roger Mills]

Yes - assuming it's not a modulating boiler - which is unlikely if it's old

There's bound to be *some* but I wouldn't worry too much. [It would be

*most* if you had a thermal store system where the boiler ran continuously until the store was hot and then shut off for a long time]

Correct. When the HW demand is satisfied, the valve moves to the CH-only position and continues to heat the radiators until the CH demand is satisfied (if it ever is!).

Yes - and your radiators would give out 75% more heat than they would with a flow temp of 60 and return of 50!

[Tim Streater]

Thanks for those answers. But for this particular Q, it appears to mean that, in the summer (i.e. when the CH is off), once the HW demand is met then the boiler will continue to run, shoving hot water through (in the general case) the bathroom towel rad(s) unnecessarily. Then if my boiler can't reach 80C it'll just run on and on until the programmer timing settings cut it off. Hmmmm.

[Tim Streater]

Thanks. That's another useful suggestion for me to follow up. And yes, I'd say there *is* room for improvement.

[Roger Mills]

No! That's not how it works. If there's no CH demand, the valve will never move off the HW position. In this position, the boiler is controlled by the cylinder stat on the HW tank, and will go off once the demand is satisfied.

[The logic of Y-Plan systems is actually quite complex because that position of the valve is determined by which demands are present[1] *and* in CH mode (but not HW mode) the valve plays a part in switching the boiler on]. [1] HW only - HW position, HW+CH - mid position, CH only - CH position

[Tim Lamb]

In message , harry writes

Plumber and housewife seem to prefer vertical.

regards

[Tim Streater]

Ah! So it's cleverer than I feared it might be. That's good - thanks.

Today the boiler man suggested checking the CH header tank to ensure that the float hasn't jammed, and turning the pump down from III to II. We'll see how that affects matters.