Advice regarding balancing of small system

[richardc1983]

Hey everyone.

I read the FAQ article on how to balance radiators but I think I need to clarify whether it was necessary on my system. I want to run the system as efficiently as possible in my 2 bedroom 1930's end terrace.

I have a gloworm 30cxi (30kw) condensing combo boiler connected to 6 radiators... (Small hall, lounge, kitchen, 2 bedrooms and bathroom). 1 is a double, 1 is a long one but single panel, then the others are all medium single panelled with one small one in the hall and towel rail in bathroom.

Currently the lock shield valves are pretty much fully open on all the rads and we run with a flow temp of approx 40-45c this keeps the house at a comfortable 20-21c throughout. All rads have trvs and to be honest the upstairs bedroom ones only come on briefly as they are kept low at the 19c setting.

The question is do I need to regulate the lock shield valves to make the system more efficient or due to the size of the system I need maximum flow through all the rads to ensure of a low flow temp back to the boiler to avoid the boiler short cycling because I have slowed the flow rates through an already small system. The house isn't a big house but you may think 6 radiators are big? The boiler is 30kw output though.

The house is cavity wall and loft insulated to current standards. So it's a warm house really. I do tend to run the heating for longer periods at the low flow temp as it keeps a nice even temperature.

Any advice gratefully received I have read many conflicting posts saying to balance and not balance and want to know what's right for my system. My concern is if the flow is reduced through the radiators then the trv's reach temp and close off then the flow to the radiators calling for heat is still not at it's full potential because the lock shield valves are also reduced on those.

Obviously if I had problems with any radiators heating up then I would need to balance but they all reach the same temp within 15 minutes.

Thank you.

 

[D_Hailsham]

How long have you lived in the house?

Were you there over the last winter?

Do the room temperatures stay the same or do they tend to fluctuate?

6 rad will be about 9kW.

The boiler needs to be 30kW so you get adequate hot water.

If the LS valves are full open the system has never been balanced. You would have to close them down to about 1 turn open before you noticed any difference and probably as a quarter to half turn open to have any real effect.

It's not a case of needing the maximum flow through the rad but the correct flow.

 

[richardc1983]

How long have you lived in the house?

Were you there over the last winter?

Do the room temperatures stay the same or do they tend to fluctuate?

6 rad will be about 9kW.

The boiler needs to be 30kW so you get adequate hot water.

If the LS valves are full open the system has never been balanced. You would have to close them down to about 1 turn open before you noticed any difference and probably as a quarter to half turn open to have any real effect.

It's not a case of needing the maximum flow through the rad but the correct flow.

I've lived in the house since May 2012 - had it serviced regularly since etc. New fan fitted this time round along with some other parts. Yes I was there over the last winter.

Room temperatures don't really fluctuate to be honest they are pretty constant which is a good thing. When the heating is off they can drop low if its really cold outside.

Today I closed all the LS valves down and tried to balance the system. The hallway radiator I think is the first one off the boiler so this is less than a quarter of a turn from closed and the radiator still gets hot. Can you explain what you mean by the 1 turn open and quarter to half turn open to have any real effect? Do you mean like I have done on the

All the others are now approx 1 full turn from fully closed and 1 is half a turn from fully closed. Bathroom radiator is open fully as doesn't have a TRV but again i'm not sure if this should also be balanced as the boiler has a built in automatic bypass but does having the bathroom fully open mean hot water is going to be sent to that as its the least resistance due to the vales being open? I was thinking of putting the larger radiators and those further away to half a turn open then the smaller ones and those closest to the boiler a quarter of a turn? Surely on a small system such as this that will give me a pretty decent setup?

What happens to the excess supply water that is not going to the radiators does that then end up going back to the boiler or does all the supply water have to go through the radiators before it goes back to the boiler unless going through the bypass valve or bathroom rad. I don't want the boiler burner short cycling because there isn't enough heat loss through the radiators. Or does the excess water going through the radiator that is open fully lose its heat through that. I want the system to run as efficiently as possible.

When it says temperature differential across the radiator should the radiator feel cooler as it goes from one side to the other or should they all be as hot as the actual flow temp on the boiler. They are all equal temperature but I am worried I still have too much flow through them and think I should close them down but don't want to close down too much that the radiators then feel cooler generally.

Maybe i'm not understanding it right? Sorry for all the questions I have spent the last few nights reading none stop about this but there is so many opinions.

 

[D_Hailsham]

I've lived in the house since May 2012 - had it serviced regularly since etc. New fan fitted this time round along with some other parts. Yes I was there over the last winter.

Presumably the house was getting warm enough last winter (or you would have mentioned it) which means the rads are correctly sized.

When the heating is off they can drop low if its really cold outside.

Improve the insulation.

Can you explain what you mean by the 1 turn open and quarter to half turn open to have any real effect?

The typical lockshield valve is fully open, i.e at maximum flow, when it is about 1½ turns open from closed. The rest of the 2-3 turns range is just waste space.

A 15mm pipe can carry about 6kW of heat, which is a flow rate of 7.83 litres/min. If you are connecting a 1kw rad the flow needs to be reduced to a sixth of that, which means that the LS valve would have to be open approximately a quarter turn (assuming 1½ is max flow). This is only an estimate as there are other factors which affect the flow rate.

Bathroom radiator is open fully as doesn't have a TRV

It still need to be balanced

I was thinking of putting the larger radiators and those further away to half a turn open then the smaller ones and those closest to the boiler a quarter of a turn? Surely on a small system such as this that will give me a pretty decent setup?

Not a bad starting point

What happens to the excess supply water that is not going to the radiators does that then end up going back to the boiler or does all the supply water have to go through the radiators before it goes back to the boiler unless going through the bypass valve or bathroom rad. I don't want the boiler burner short cycling because there isn't enough heat loss through the radiators. Or does the excess water going through the radiator that is open fully lose its heat through that.

There isn't really any 'excess water'. Each rad will take its share of the total flow depending on the setting of the LS valve. If a valve is open too much it will take a larger portion of the flow, thus robbing other rads.

Does the bathroom rad heat up in the summer, when the CH is off?

When TRVs are closed down some of the flow will go though the boiler bypass. This because the required flow is reduced, so the pressure at the pump increases. This opens the bypass to allow the excess flow to circulate back to the boiler.

When it says temperature differential across the radiator should the radiator feel cooler as it goes from one side to the other or should they all be as hot as the actual flow temp on the boiler.

The temperature differential is between the water entering and leaving the rad. Usually checked on the pipe entering the TRV and leaving the LS valve. There will be some variation in temperature across the surface of a rad. If it is cold along the top, that's a sign of air in the rad; it needs bleeding. If it's cold at the bottom, that's a sign of sludge accumulated in the rad.

 

[richardc1983]

Ok I've tried balancing again this morning, set a 60c flow temp and tried to get the 20c across the radiators. Did it by hand rather than use the elements. I've ordered a infra red one from amazon and will check my work when it comes.

All the radiators are pretty much either 1/8 or 1/16 of a turn on. Even the large double in the lounge is a 1/16 along with the hallway. Bedroom 1 is 1/8 of a turn and spare room is 1/16. Bathroom also has been restricted down and is approx 1/16 and the kitchen about 1/8.

Getting nice differential across the radiators and a nice return flow back to the boiler. I turned it back down to 40c flow temp as it's mild usually it's about 45c and the boiler still short cycles at that temp. Can't restrict radiators any more really without turning them off some of them are so far down so I think it's the best I can achieve for a small (I think) system.

In answer to your question no the bathroom one doesn't heat up in summer. All the valves were fully open so whilst the rads used to get warm there were fluctuations in the flow temp of the boiler as sometimes radiators would feel tepid and then they would go warmer as the boiler was short cycling all the time due to the high flow rates I imagine?

 

[Agile]

An IR thermometer is pretty useless for heating work. You need a contact thermometer.

Your balancing is about right with lockshields only slightly open.

Your boiler is always going to cycle on/off because it cannot modulate down low enough to suit the low heat requirements of your house. Its sized for hot water.

You talked about differing advice on the need for balancing. All I can say is that anyone saying its not needed is an idiot! That's the trouble with these forums you cannot easily tell who is a professional and who is a troll!

Tony

 

[Galoka]

An IR thermometer is pretty useless for heating work. You need a contact thermometer.

I found using an IR thermometer was easier/quicker (not unimportant for balancing rads), and seemed accurate compared to a contact one I had around. though because of the varying emissivity of the surfaces you might aim it at (old pipe, painted pipe, shiny chrome, painted rad etc.) putting a standard target of a bit of black insulation tape where I was going to measure improved the accuracy of the measurement I think.

 

[Agile]

It is quick and easy certainly.

But it cannot easily be used on the pipes because of their small size. If I wanted to use one I would target the corners of the rad where the pipes enter. Furthermore when white painted they will never be very accurate.

The contact type with clips are the only way to get an accurate reading.

Tony

 

[richardc1983]

So if the radiators have been balanced to 60c flow temp and I then decrease the flow temp to 40/45 would I then see the same temp drop as I do at 60c flow temp? Would the lower flow temp mean that the radiators will feel cooler as we get from one side to the other whereas currently they are quite balanced?

 

[Agile]

If you significantly reduce the flow temperature like that then the heat loss will reduce and so the temp diff across the rad will also reduce.

But that's of no practical significance because the boiler is already in maximum condensing mode as soon as the return is below about 45 C.

Tony

 

[richardc1983]

If you significantly reduce the flow temperature like that then the heat loss will reduce and so the temp diff across the rad will also reduce.

But that's of no practical significance because the boiler is already in maximum condensing mode as soon as the return is below about 45 C.

Tony

So I am assuming if the rads are equal temp balanced at 60 When I operate the boiler with the lower flow temps if the rads are significantly cooler at either end I will open valves ever so slightly?

 

[Agile]

No don't touch them!

Its only important to have them balanced correctly at the higher flow temps when the return temperature needs to be lower to achieve the best efficiency.

Tony

 

[richardc1983]

No don't touch them!

Its only important to have them balanced correctly at the higher flow temps when the return temperature needs to be lower to achieve the best efficiency.

Tony

So if I find rooms are not warm enough because the rads are not equally hot when at the lower flow temps whereas when they were open the rooms were what do you suggest I do? Increase flow temp when before it was enough? This would cost more to run then.

 

[Agile]

The heat output will still remain in the same proportions from room to room as you reduce the room temps.

Heat output is roughly proportional to the average rad temperature.

Tony

 

[richardc1983]

The heat output will still remain in the same proportions from room to room as you reduce the room temps.

Heat output is roughly proportional to the average rad temperature.

Tony

So it shouldn't affect it really?