Problems Balancing Radiators

[slippyr4]

Hi All,

Finished my DIY complete CH/DHW install a few weeks ago, the boiler was installed by my CORGI plumber. I'll summarise the system:

3 Bed 1930's semi. Worcestor-Bosch 24i System boiler, Conventional DHW cylinder, Danfoss controls with 3 port mid position valve. The valve is located in the airing cupboard in bedroom 3. My CH pipework tees under the bedroom floor, one pipe goes downstairs, the other services upstairs rads. The tee that goes downstair's first port of call is the hall, which has no TRV and a roomstat, every other rad has a TRV. All my "trunk" pipework is 22mm copper, I tee down to 15 for every rad.

After the boiler install I hadn't got round to balancing the radiators. I've been trying to do this a little bit tonight - because I noticed earlier when I switched the heating on (it had been off most the day), most the rads in the house were hot well before the rad in one of the bedrooms (which is the last in the chain). I reasoned that the downstairs radiators were starving the upstairs of heat, so balancing to restrict their flow was in order.

I started with the (non TRV) rad in the hall. I don't have proper pipe thermometers, so my crude approach is two (identical) digital thermometers with the sensors taped to the pipes, and a sleeve of pipe insulation over the top. It may not be calibrated but I reason that for temperature difference readings, it'll do.

Anyway, I found that the (unbalanced) rad in the hall had a 0.5 degree temperature drop, which is unsuprising with the valves wide open. So, I wound them back and now have a 10 degree drop across that rad. All good.

Next radiator to balance is in the lounge. This is the next radiator in the downstairs loop, and it's the biggest radiator in the house (with a 2.4 KW rating). I took the TRV head off, so that the valve is wide open. Attached the thermometers, and found that the temperature drop with both TRV and lockshield wide open was 14 degrees. This suprised me. I thought that with the pump whizzing along, wide open valves would give small temperature drops.

So, my question - is that normal? for really big rads to have a huge drop and consequently no benefit to winding down the valves at all?

Or, if I go on and balance the other radiators, will this one get more flow and hence the temp. drop reduce?

Or, do I need to turn the pump speed up? It's on setting 2 at the moment. The boiler appears to be quite well modulated back - it's not exactly working hard at all.

Or is there anything i'm missing?

Grateful for any help

thanks

Slip

 

[gazthepottertonengineer]

i think you should get award for longest post ever

couldnt be bothered to read it all properly but yes i personally would put pump on speed 3

 

[chrishutt]

I couldn't be bothered to read it all either!

Tip - Your first post should be short and sweet, a kind of bait. Once you've got one or two of us hooked, you can add in the detail as required.

 

[Slugbabydotcom]

So, my question - is that normal? for really big rads to have a huge drop and consequently no benefit to winding down the valves at all?

A larger rad has more surface area therefore will suffer a greater temperature drop.

All this rad temp carry on is a bit overkill in my book The idea of having a heating system is to keep a building warm Focus on the end product! ... When it doesn't keep you warm is when you should look into it.

When balancing rads just do it so that they all get warm. If any dont get warm thats when they are not working.

PS I like your essay style. even though others dont. Saves me making assumptions and going off on a tangent

 

[chrishutt]

A larger rad has more surface area therefore will suffer a greater temperature drop.

The whole point is to avoid this by balancing the flows to ensure that each rad has more or less the same temp. drop irrespective of its size.

And the actual rad temperature does make a big difference. The average temperature of a "warm" rad might be anything between 40C and 80C (both temperatures would feel hot to touch). Yet in a room at 20C temperature, the heat output at 80C would be three times what it would be at 40C.

 

[Slugbabydotcom]

40º isnt warm .... its luke warm!
I would class warm as around 50º and up
Anything much over 60º is now considered unsafe due to likelihood of scalding

When a room has reached its temperature the TRV closes off thus 'autobalancing' the system until all the rooms are warm. So unless you have a room that is taking far too long to warm up then why worry?
In pre TRV days balancing was a bigger issue
Im not saying dont bother balancing at all either but just do it near enough by touch and the TRVs will look after the rest
Be as scientific about this as you like but the whole point is a warm house

 

[chrishutt]

Anything much over 60º is now considered unsafe due to likelihood of scalding

This applies to DHW, not to central heating water. Max flow temps. on boilers are 82C, although you only need this in the coldest weather.

Still a rad at 80C gives out twice the heat as a rad at 50C! As for TRVs auto-balancing, this doesn't account for rads without TRVs (where room stat is) nor for the heat-up period before TRVs cut in.

 

[slippyr4]

When a room has reached its temperature the TRV closes off thus 'autobalancing' the system until all the rooms are warm. So unless you have a room that is taking far too long to warm up then why worry?

That's exactly why I didn't bother balancing previously. But, yesterday I found that the last radiator in the upstairs loop didn't get even slightly warm for quite a while after the heating was turned on.

Because all the TRV;s were wide open, the water was taking it's easiest route, ie lowest resistance route, which was the downstairs loop.

My logic is that throttling back these downstairs radiators will force more water through the upstairs loop, which will allow those radiators to heat up immediately, and thus all the TRV's can do their job.

This seems to be a great demonstration of TRV's not being a substitute for balancing.

BUt the question was the confusion over the big rad. I'm now speculating that maybe that radiator isn't getting as much flow as it might, and things will improve if I balance all the other radiators because they will then become more restrictive.

cheers

slip

 

[ricarbo]

I think you need to carry on with the balancing, then go round again, and maybe again. Take your time to let things stabilise. If that rad still has an excessive drop, there isn't enough flow to it. Remedy is larger supply pipes, less elbows, machine made bends, higher pump speed. The sizing of pipes is explained on the copper development agency site leaflets. Worth a read. Too big sludges up, too small not enough heat.

 

[Slugbabydotcom]

I found that the last radiator in the upstairs loop didn't get even slightly warm for quite a while after the heating was turned on.

This seems to be a great demonstration of TRV's not being a substitute for balancing.

Close all the other rads off completely to establish a flow to the one that doesnt work. The pipes to it will be blocked with air. debris or pipe restriction.

If a circuit is badly restricted then its possible that no amount of balancing will work.

When you balance the sytem after re-establishing the flow to this problem rad; just open all the other rads LS valves a half turn. Run the system for half an hour and open the valves to any lukewarm ones a little more.

Carry on slightly opening LS valves to the cold ones and slightly closing LS valves to the very hot ones until the system is evenly warm. Make sure all trvs are fully open whilst balancing and allow time for the system to settle as you work on it.

 

[slippyr4]

I'm pretty sure it's not blocked. The system is brand new, and was powerflushed fully. There is no air to be heard in it, and no more air comes out of any of the rads.

The radiator does get hot, but only after the other ones have already been hot for a while. This one rad is at the end of the longest pipe run, so I think just the length of pipe is causing more restriction that the unbalanced radiators (hence wide open) downstairs.

I installed a lever-type ball balve in the 22mm flow that goes from upstairs to downstairs. If I close this valve, so the the entire heating loop is upstairs only, then this rad gets got immediately.

 

[Slugbabydotcom]

Try taking the rad off and flushing some water through each rad valve into a washing up bowl to make sure there is adequate flow through each pipe

 

[slippyr4]

Try taking the rad off and flushing some water through each rad valve into a washing up bowl to make sure there is adequate flow through each pipe

I'll try that at the weekend, see what happens.

Thanks for your help slug.