Trying to balance new boiler not properly setup by installer

[bhm1712]

IR thermometry is not inaccurate unless you buy a maplins £10 special!!

All surfaces must be the same in order to measure accurately. i.e - preferrably for pipes, use white insulation tape and wrap it wround the pipe your going to measure, as pointing it at bare copper is no good. If all the flow and returns are already painted white your ok.

 

[Kaymo]

Thanks for the replies folks a lot of good information there. I appreciate you all taking the time.

I have found the IR thermometer to be reasonably accurate, but you do need some tape on the pipes to get an accurate reading and it is fiddly – wouldn’t want to do it regularly with this. Based on the known temp coming out of the boiler and checking the readings on the pipe there I am confident that the readings are close enough for this purpose.

I have balanced the whole system now, took ages with so many rads but the with all the TRV’s fully open and the system up to temp the last two rads were fairly close to fully hot with the their lock valves fully open. From this I don’t think that the boiler is over or undersized, I think its probably fairly close. Even if it is slightly undersized I don’t usually have any more than half the rads on at one time anyway. I also checked the differential at the boiler and its almost exactly 20 deg.

I had went through the boiler sizing exercise before I got the boiler fitted as different heating engineers were recommending greatly varying sizes and I was getting something between 28 and 32kW. This boiler I believe has 32kW available to the heating system. I also thought that given 20 radiators and approx. 1.5 kW from each that this was an approximate match too. Its difficult to make any assumptions about the output of the rads as some are fairly old without the convecting fins and some are brand new.

When I checked the temps at the boiler I was getting 85 and 65 and although I believe this means that the system is balanced, I also understand from what I have learned here that this means that the boiler won’t be running in condensing mode so I have turned it back a bit and will check it tomorrow from cold and set to about 70 deg output for now – although I might need to turn the output back up again if we get a winter like last year, it was -18 deg here one day last year.

Hopefully that’s it, I presume that changing the boiler output temp wont affect the balancing but I will check all again tomorrow running up from cold.

It is a little frustrating having to do this after paying nearly £3k for a boiler to be fitted. I would have thought this reasonably good value if it was all done right first time. On the upside I do know a good bit more about my heating system than I did last week!!

 

[bhm1712]

we use IR thermo's at work and they are calibrated to within +/- 1% accuracy so that proves they are ok. We use them for measuring the temperatures of CIP system dead legs after a sanitisation washout.

 

[D_Hailsham]

IR thermometry is not inaccurate unless you buy a maplins £10 special!!

But all you are really measuring is the differential, the actual temperatures are not relevant.

All surfaces must be the same in order to measure accurately, i.e - preferably for pipes, use white insulation tape

IR thermostats are calibrated to a surface with an emissivity of 0.95, which is approximately equivalent to that of black insulating tape.

The IR may give a consistent reading but is unlikely to be accurate ( unless you paint your rads matt black! )

You do not measuring the temperature off the surface of the radiator, but off the flow and return pipes immediately below the valves.

 

[spudkey]

If you follow that procedure and still cant get the last radiators to heat to max temp then the installation is faulty in terms of sizing. You asked if it may be oversized, its more likely undersized at 30Kw if the house is as big as i think it is, and has 20 ish rads. My mother has a 36kw boiler for 17 radiators and British gas initially fitted a 24Kw boiler which they had to rip out under warranty because they sized it wrong. No matter how much they tried to balance, they couldnt get the heat to the last few rads and when hot water was on....well lets just say it didnt work

Rubbish, why would a bigger output boiler get heat to furthest rads, its down to flow rate and resistance not boiler output.

If a modulating boiler lowers its output you dont loose heat to the furthest rads

 

[Kaymo]

Sorry to drag this up again but after having completed the balancing at the weekend and putting the TRV's back to their normal state (most of them in rooms we dont use are set to frost or 1) I checked the radiator temp drop again and on the few that are still on full the temp drop is now less than 10. I also noticed that the differential at the boiler is now 15 degrees and and not 20 as it was when balancing at the weekend. Is this what would be expected and due to the fact that 50% of the radiators are off in normal operation or could it be becuase I have dropped the radiator output temp after balancing the radiators?

If this is normal for the balance on the rad to change when the others switch off, I am wondering if it would be better to balance the system in the state that I would normally use it rather than with all radiators on full?

I also have noticed that since turning the boiler output down to 70 deg as recommended for efficiency the living room is struggling to heat up. I have turned it back up a bit but understand that if the return temp is above 55 deg it wont condense. It seems that I may have to choose between efficiency and having a warm room!

 

[D_Hailsham]

after having completed the balancing

What procedure did you follow?

 

[Kaymo]

All lock valves and TRV's fully open CH on, gradually closed valves until temp drop between inlet and outlet pipes on radiators was 15-20 deg C. Verified it all again the next day that all radiators had same temp drop with all TRV's open and that boiler drop was 20 degree C exactly.

All I have changed since then is to put the TRV's back to there normal settings and turned temp output on boiler down from 85 to 70 deg C.

 

[Agile]

If you are turning many rads off then the pump pressure increases and the flow increases and the diff reduces.

If you want to be really technical then you can adjust the auto bypass ( whats that ? ) so that it balances the flow at the same rate as the unused rads. But that would reduce the diff across the boiler which is not desireable.

To maintain efficiency you will have to adjust the balance for those you are using ( perhaps plus the one extra you are most likely to use ).

Your rad is undersized at current settings if it does not make the room warm enough. Consider increasing insulation.

On the coldest days you can turn the flow temp up a long as you remember to reduce it as soon as possible. Thats what weather comp does automatically.

Tony Glazier

 

[Kaymo]

Thanks Agile, I though that something in the dynamic must have changed by turning off the other rads hence the reason they tell you to have all the rads open when balancing. I was trying to get my head around it as I was thinking that the pressure would be determined by diameter of the return pipe but I suppose that with all the valves open there is a much greater mass of water for the pump to push around the system. I'll balance it again with just the rads that are in regular use open.

There are actually 3 radiators in the room in question, two of them large doubles and its only an average sized living room. I have just found out this morning that my wife had left the stove door in that room ajar and this may have been causing a draft last so this might have been part of the problem.

Insulation in the short term is not really an option. I have already insulated between the joists under the floor so to do any further insulation would involve pulling down the interior plaster (1905 construction no cavity walls).

 

[D_Hailsham]

All lock valves and TRV's fully open CH on

Yes , you must have all TRVs open by removing the heads, which prevents the TRV influencing the balance. But you should start with all LS valves closed.

Read How to balance a CH system, which is an expanded version of the instructions provided by Drayton.

 

[Agile]

Many people do not use their windows/curtains in the optimum heat loss position.

Then 98% of open fireplaces I see have an open chimney which is constantly sucking 20% of the heat ut of the room.

In very cold and windy weather its essential to ensure there are no draughts spoiling the heating.

Tony

 

[Kaymo]

All lock valves and TRV's fully open CH on

Yes , you must have all TRVs open by removing the heads, which prevents the TRV influencing the balance. But you should start with all LS valves closed.

Read How to balance a CH system, which is an expanded version of the instructions provided by Drayton.

Thats interesting as other instructions that I have seen have said to start with all valves open. Regardless of which way it is done though, when I finished I went back around all of the radiators and they all had a temp drop of 15-20 Deg C. I also checked them again the next day while the system was warming up and they were still balanced at 15-20 deg C so I am confident that the system was balanced correctly before I shut off the rads in the empty rooms. I think the issue is as Agile has said that with over half of the radiators shut in normal operation it may make more sense for me to balance it with only the rads that are normally open.