Balancing radiators Vs biggest and furthest away rad.

[rarara]

So i want to re-balance my rads generally, as over the past couple of years a few have been replaced/added. The slight issue I have however is that the coldest room (lounge - so the one we would generally want to sit when the heating is on during an evening) which just happens to be furthest away from the boiler also has the largest radiator, and this also happens to be the one which is slowest to heat-up, as well as being very slightly cooler at the bottom than the top.

The valve is fully open on this rad, so I have no wiggle room there to make any further gain. If I was going to balance eveything I would use the 'standard' 20 degree flow/return method starting nearest to the boiler, but my question is:

If I find all the other rads (which get plenty hot btw) are balanced, how do I make sure the lounge rad gets a disproportionate amount of heat so warm quickest (or at least as quick as the others)??

I could always balance all the others, then close them off 1/4 or 1/2 a turn for example, but that doesn't seem very scientific. Is there a way of say balancing the largest with a 20 degree flow/return difference, but use a different temp difference for the rads which are nearer the boiler?

Thanks

 

[endaxi]

I had the same problem a while back. I cured it by screwing down the lockshields on the rads that got hottest (and hot quickly), generally the upstairs. Some are only open 1/8 to 1/4 turn whilst others (downstairs and furthest from boiler) are fully open. I also have TRVs set to 3 or 4 upstairs so that they periodically close and allow more 'oomph' to the big rads downstairs. It worked for me and the family say the house is warmer than it's ever been. I got good results fast and then tweaked here and there to get exactly what I wanted. It's a bit of 'rob Peter to pay Paul.

 

[John D v2.0]

I think you're misunderstanding balancing, there's no need to consider how much "heat" each radiator needs, but you need to balance them all not just the ones closest to the boiler, especially including the ones that are not working correctly. If you make sure all radiators are dropping the same number of degrees e.g. 20c, they are all getting the design amount of heat, and are all balanced. But you have to start at the one furthest away from the boiler which is the one with the largest drop with all the valves fully open.

If you are still cold, and the drop is correct, then you need a bigger radiator or more insulation. If the drop is too high on the distant radiator even with all the others turned off, then the headloss on the long circuit is too much for the pump or the bypass is opening too soon so you either need to turn up the bypass pressure/a bigger pump which could be noisy, or less resistance on the pipes i.e. bigger or cleaner pipes.. If the radiator has cold spots but the right temp diff then you may have a mucky radiator.

 

[Nige F]

turn pump to max.

 

[rarara]

But you have to start at the one furthest away from the boiler which is the one with the largest drop with all the valves fully open.

This seems to contradict conventional wisdom about starting with the closest. Right now the furthest/biggest is fully open and I feel it isn't getting as hot as the others (not that the room isn't getting hot - that's a separate consideration). I was therefore looking to, as endaxi said, "rob Peter to pay Paul" by possibly throttling the others a bit more in comparison.

 

[Elkato531]

If you live in the property, you have the advantage of having hours, days even weeks to play around and get things right. Start by closing all rads except the slowest one and check that it heats up properly on its own. If it doesn't, you're going to have problems setting up the whole system. Now progressively open the other rad lockshields about half a turn at a time until they heat up correctly. If you can't get all the other rads up to temp without compromising the performance of the problem one, then you have a pump head, circulation issue which needs addressing.

 

[D_Hailsham]

I think you're misunderstanding balancing

The convention that a system is 'balanced' when each rad has the same temperature drop assumes that every rad is exactly the correct size for the heat loss in the room. But, in the real world, this is rarely the case. Rads are frequently oversized, e.g the same length as the window where they are fitted - because it looks 'better'. Or they may now be oversized because the insulation has been improved.

There nothing wrong with changing the output of a rad by adjusting the LS valve to give a lower/higher return temperature. It also has the advantage that the rad's TRV will have an easier job of controlling the room temperature.

 

[Grumpy Gasman]

I think you're misunderstanding balancing, If you make sure all radiators are dropping the same number of degrees e.g. 20c.

I’m not sure that you understand it either.
System may well have been sized for a 10c dt.

But you have to start at the one furthest away from the boiler

...or possibly the pump.
Always start at the radiator with least friction/head loss.

 

[endaxi]

This seems to contradict conventional wisdom about starting with the closest. Right now the furthest/biggest is fully open and I feel it isn't getting as hot as the others (not that the room isn't getting hot - that's a separate consideration). I was therefore looking to, as endaxi said, "rob Peter to pay Paul" by possibly throttling the others a bit more in comparison.

I read-up on balancing and watched videos on U-tube but it seemed over-complicated. I also think I have manifolds so the 'nearest' and 'farthest' rads are hard to pinpoint. I asked a question on here... https://www.diynot.com/diy/threads/blocked-manifold.488622/ and followed the advice of choking the hot rads to get the cold ones hotter to good effect.

 

[andytw]

I bought an infrared thermometer on offer from Screwfix, Triton I think, less than £20. Works well on the white paint of radiators.
I open all L/S valves and remove TRV heads, then turn the heating on.
Then, once it is warming up, I go around all rads and note temperature at centre top of each one.
Expect readings like 58, 56, 52, 53, 48, 50.
Some will be cooler and some hotter.
I write them all down.
I then close down the hotter ones to maybe 1 turn open (2 or 3 turns is a waste of time). In the above example I would just adjust the first 2.
After 5 mins I go and measure again, re-note the readings and again throttle the hottest rad(s), it will usually be the ones already adjusted so another 1/4 turn would be in order.
I can usually and quickly get them all within a couple of degrees of each other and I then refit the TRV heads. Obviously if a room remains too cool the radiator is undersized.

 

[John D v2.0]

If you make sure all radiators are dropping the same number of degrees e.g. 20c,

I’m not sure that you understand it either.
System may well have been sized for a 10c dt.

That's what "e.g." means. And given the op is having trouble with flow rates it makes sense to try balancing to a higher drop. Starting with the last rad might help with working out what the achievable drop would be on their system.

Always start at the radiator with least friction/head loss

Well you could if you're sure you'll have enough for the drop you're aiming for, in reality it's an iterative process, personally in this situation I'd start with only the furthest rad on and then if that doesn't get enough turn up the pump and/or bypass as needed. If that's possible I'd start opening up closer ones.
If it's a manifold system the head should be maintained fairly well but if there's a lot of shared pipework it may not be possible to get enough at the end once they are all on.
But as stated by others the op can carry on tweaking at their leisure!

 

[John D v2.0]

The convention that a system is 'balanced' when each rad has the same temperature drop assumes that every rad is exactly the correct size for the heat loss in the room

All very true in your post. You make a good point you can unbalance a system increasing the drop on a larger rad to more closely match the average temperature needed to heat the room.
If the trv is nearly closed it may have the same effect actually!

 

[D_Hailsham]

If the trv is nearly closed it may have the same effect actually!

It's much better if the flow is set using the LS valve - unless the TRV has built-in balancing, as with the Drayton TRV4 and Honeywell Valencia range. Incidentally the Valencia has a recommended max opening of less than one turn for balancing. Compare that to the earlier suggestion that balancing should be done in half turn steps.