Boiler / Radiator BTU Delta - Should I be using T50 or T60?

[GeddyMortgage]

New rads are based on 50 deg.
as a 60deg rad, it will emit 26% more heat. or a factor of 1.26, (60/50)^1.3
A 30deg rad will emit 51.5% of a 50deg rad, a factor of 0.515, (30/50)^1.3, you would need to oversize it by a factor of 1.94, (1/0.515) to emit the same as a 50deg rad.

Thanks, when you say 'new' how new do you mean? Could it be the ones from 2008 in this property were also 50 deg? And how do I know the new ones I want to buy are rated this way?

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[JonathanM]

Thanks, that made sense to me (finally!)

:- Yes only replacing radiators in the ground floor hall/dining room. They were all double panel double convector types and will be done away with, likely in place of Triple column ones of a similar height/width....the ones on the 1st floor/top floor will all be staying the same (all of those are double panel single convector types)

:- Flow temperature, is the LCD temperature readout on the boiler? We've got it set to MAX and the temp readout peaks at about 84degrees.

:- Did it keep the house warm in december? Some areas, yes, some areas not so much, the hall struggled and we've just opened that up to a much larger space as per the renovations, hence why Im looking to swap out / and add radiators to that area. It had 3 in there, I'd like 5 in there.

Were all the radiators in the house working properly. Were they hot evenly all over, top and bottom. Also, at that flow temperature, they should have been almost too hot to touch?

And what sort of room temperatures were you wanting/achieving. Do you have TRVs on the radiators. If so, were any of them cutting the radiators off.

T60, T50 etc. refers to the difference between the average temperature in the radiator and the room temperature. So, if water goes into the the radiator at 85C and comes out at 75C, the average radiator temperature is 80C. If the room temperature is 20C, then that is a T60 output.

If all the radiators were hot and working properly at the same time, and the boiler temperature was running at 80C+, then you are probably looking at a T60 scenario. If you calculated that at T60 your radiators were giving out 38KW, then you might actually have been approaching the maximum output of the boiler after all. But that would be an enormous heating requirement.

 

[GeddyMortgage]

Were all the radiators in the house working properly. Were they hot evenly all over, top and bottom. Also, at that flow temperature, they should have been almost too hot to touch?

And what sort of room temperatures were you wanting/achieving. Do you have TRVs on the radiators. If so, were any of them cutting the radiators off.

T60, T50 etc. refers to the difference between the average temperature in the radiator and the room temperature. So, if water goes into the the radiator at 85C and comes out at 75C, the average radiator temperature is 80C. If the room temperature is 20C, then that is a T60 output.

If all the radiators were hot and working properly at the same time, and the boiler temperature was running at 80C+, then you are probably looking at a T60 scenario. If you calculated that at T60 your radiators were giving out 38KW, then you might actually have been approaching the maximum output of the boiler after all. But that would be an enormous heating requirement.

Were the rads running properly? :- Bit of a mix, some boilers evenly hot, some hotter at the top than the bottom. Yes too hot to touch, well certainly too hot to hold for a number of seconds.

What room temp did I want/achieve - Ideally a temperature of 17degrees would've been ample, generally speaking we'd put the heating on for a couple hrs over winter and see it climb 4-5degrees. Apart from the really cold snap.

Re:T60 - I assumed based on the calculations i'd done online (i appreciate someone else has mentioned this may well be an out of date way to calculate) that I was at 38kw @ T60.... As when the property was extended upwards, all the radiators that occupy the extended floors are single panel single convector, oppose to the 'original' bungalow ones all being double panel/double convector. It looks like someone had took the max load into account when extending. It does seem like a high load, I keep thinking about that, but there are 23 rads in total.

One other thing I wanted to ask - As this is a conventional central heating boiler with an unvented hot water tank, surely I can't lower the flow temperature too much without risking the hot water tank temperature going below 60c and running the risk of legionnaire's disease etc? So I guess with this setup im a bit limited in how low I can run the flow temp?

 

[Johntheo5]

Thanks, when you say 'new' how new do you mean? Could it be the ones from 2008 in this property were also 50 deg? And how do I know the new ones I want to buy are rated this way?

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Create a look that stands out from the crowd with the Milano Windsor horizontal triple column radiator. Sure to create a bold yet sophisticated look, this radiator features a classic column design and a resilient metallic finish that will look like new for many years.The Windsor column radiator...

www.bestheating.com

Thanks, when you say 'new' how new do you mean? Could it be the ones from 2008 in this property were also 50 deg? And how do I know the new ones I want to buy are rated this way?

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Create a look that stands out from the crowd with the Milano Windsor horizontal triple column radiator. Sure to create a bold yet sophisticated look, this radiator features a classic column design and a resilient metallic finish that will look like new for many years.The Windsor column radiator...

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Don't think the UK adopted the T50 standard until 2013 so more than likely that your rads are T60s. The new ones, unless otherwise stated, will be T50s. If a T60 rad's output is satisfactory then you would multiply by a factor of 1.27 as T50 will emit 79% of the same size T60.
Your boiler will probably show the boiler return temperature on some menu or other, if you are running the rads with both isolating valves fully open then a rad dT of 10C would fairly typical so the rads with a flowtemp of your 84C would be quite close T60, (84+74)/2) minus 20 = 59C.

 

[JonathanM]

Thanks, when you say 'new' how new do you mean? Could it be the ones from 2008 in this property were also 50 deg? And how do I know the new ones I want to buy are rated this way?

I think what it means is that if you see a radiator advertised these days giving a particular headline output, then that output will almost always be based on T50. But that same radiator will also have a T60 output and a T30 output.

It doesn't really matter I think in your case how the 2008 radiators were identified at the time. All that matters is that you can now compare them against the new ones you want to buy

The ones you want to buy seem to have ratings for T30, T50 and T65. If you measure the three radiators you have removed, I'd be happy to see if I can find some consistent information on what their outputs are approximately.

 

[GeddyMortgage]

Don't think the UK adopted the T50 standard until 2013 so more than likely that your rads are T60s. The new ones, unless otherwise stated, will be T50s. If a T60 rad's output is satisfactory then you would multiply by a factor of 1.27 as T50 will emit 79% of the same size T60.
Your boiler will probably show the boiler return temperature on some menu or other, if you are running the rads with both isolating valves fully open then a rad dT of 10C would fairly typical so the rads with a flowtemp of your 84C would be quite close T60, (84+74)/2) minus 20 = 59C.

thanks, so is it a simple case that if I lower the flow temp / turn the gauge down on the boiler so it's running at 70c (instead of 84c) that is essentially me running at T50?

Or is it that newer rads are just more efficient with a view to more naturally operate at a lower temperature?

 

[GeddyMortgage]

I think what it means is that if you see a radiator advertised these days giving a particular headline output, then that output will almost always be based on T50. But that same radiator will also have a T60 output and a T30 output.

It doesn't really matter I think in your case how the 2008 radiators were identified at the time. All that matters is that you can now compare them against the new ones you want to buy

Yeah that's right, as those rads are advertised with the /3 different BTU/3 wattage outputs. Is that basically saying, if I run my boiler at 85c flow temp, i should use the T60 calculation for wattage? and use the T50 if I run my boiler at 70C?

The ones you want to buy seem to have ratings for T30, T50 and T65. If you measure the three radiators you have removed, I'd be happy to see if I can find some consistent information on what their outputs are approximately.

Really appreciate the help, the ones that came off on the ground floor, are as follows

type		Width mm		Height mm	BTU t60 (estimate)
Single Panel Single Convector		800		600	2545
Double Panel Double Convector		1600		600	9771
Double Panel Double Convector		1200		450	5496
Double Panel Double Convector		1000		450	4580
Double Panel Double Convector		700		600	4247
Double Panel Single Convector		1000		450	3614

 

[JonathanM]

Yeah that's right, as those rads are advertised with the /3 different BTU/3 wattage outputs. Is that basically saying, if I run my boiler at 85c flow temp, i should use the T60 calculation for wattage? and use the T50 if I run my boiler at 70C?

Exactly. These outputs all depend on how hot you run your boiler.

 

[Johntheo5]

thanks, so is it a simple case that if I lower the flow temp / turn the gauge down on the boiler so it's running at 70c (instead of 84c) that is essentially me running at T50?

Or is it that newer rads are just more efficient with a view to more naturally operate at a lower temperature?

The rads are just a lump of metal and the heat they emit is purely dependent on the difference between the mean metal temperature and the air (room) temperature. Even with a flowtemp of 84C if you reduce the return temp to 56C you will still have a T50 rad. I run my boiler (non condensing) at 75C and i often see a boiler return of 40C (TRVs on all rads) so my rads are then effectively T38 rads, but yes, reducing your flowtemp will reduce the rad output.
For example, if you reduce the flow temp to 70C you will have a T40 rad with a return temp of 50C, if you reduce it to 57C you will have a T30 rad with a return temp of 43C (with very high boiler efficiency).

 

[Johntheo5]

Yeah that's right, as those rads are advertised with the /3 different BTU/3 wattage outputs. Is that basically saying, if I run my boiler at 85c flow temp, i should use the T60 calculation for wattage? and use the T50 if I run my boiler at 70C?



Really appreciate the help, the ones that came off on the ground floor, are as follows

type		Width mm		Height mm	BTU t60 (estimate)
Single Panel Single Convector		800		600	2545
Double Panel Double Convector		1600		600	9771
Double Panel Double Convector		1200		450	5496
Double Panel Double Convector		1000		450	4580
Double Panel Double Convector		700		600	4247
Double Panel Single Convector		1000		450	3614

If you wish to run the new rads as T30s then to get the same output as the above requires multiplying the above BTU outputs by a factor of 2.5 (2.46) = (60/30)^1.3.

 

[GeddyMortgage]

(deleted)

 

[GeddyMortgage]

The rads are just a lump of metal and the heat they emit is purely dependent on the difference between the mean metal temperature and the air (room) temperature. Even with a flowtemp of 84C if you reduce the return temp to 56C you will still have a T50 rad. I run my boiler (non condensing) at 75C and i often see a boiler return of 40C (TRVs on all rads) so my rads are then effectively T38 rads, but yes, reducing your flowtemp will reduce the rad output.
For example, if you reduce the flow temp to 70C you will have a T40 rad with a return temp of 50C, if you reduce it to 57C you will have a T30 rad with a return temp of 43C (with very high boiler efficiency).

Makes sense, couple questions off of that then to make sure I understand correctly.

:- If I drop the flow temp to 57c (down from 84c) to run the rads at T30, can I add a load more rads into the property as the output of each would be lower than current (t60)?.....and.....what would happen if I did that then turned the boiler back up to max (84c flow temp)?


:- To keep the flow temp high but the return temp at 56C is it simply a case of turning all the rads down a bit?

:- Asked this above but incase it didn't get seen - As this one is a conventional central heating boiler with an unvented hot water tank, is it right that I can't lower the flow temperature too much without risking the hot water tank temperature going below 60c and running the risk of legionnaire's disease etc? So realistically can't lower the flow temp below maybe 70c?

 

[Johntheo5]

If you wish to run the new rads as T30s then to get the same output as the above requires multiplying the above BTU outputs by a factor of 2.5 (2.46) = (60/30)^1.3.

Makes sense, couple questions off of that then to make sure I understand correctly.

:- If I drop the flow temp to 57c (down from 84c) to run the rads at T30, can I add a load more rads into the property as the output of each would be lower than current (t60)?.....and.....what would happen if I did that then turned the boiler back up to max (84c flow temp)?

As you will have sized the rads to give 30253 BTU, 8.87kw at T30 then this means they are sized to give 21.82kw, (8.87X2.46), at T60 so if you turned the boiler temp back up to 84c, the rad/boiler output will be 21.82kw.

:- To keep the flow temp high but the return temp at 56C is it simply a case of turning all the rads down a bit?

Yes, you throttle down the lockshield valves.

:- Asked this above but incase it didn't get seen - As this one is a conventional central heating boiler with an unvented hot water tank, is it right that I can't lower the flow temperature too much without risking the hot water tank temperature going below 60c and running the risk of legionnaire's disease etc? So realistically can't lower the flow temp below maybe 70c?

You only need to heat the entire cylinder to 60C once per week. You can do this either manually or if your boiler is suitable you may be able to install Hot Water Priority where the CH is set to whatever temperature you require and when HW is required the boiler automatically changes the boiler setpoint to 80C and then reverts back once the HW cylinder is up to 60C.
If you leave the boiler at 70C then realistically as you can't get much lower than a rad dT of 6C then you have a T47 rad, (70+64)/2) minus 20, to give 73% of its T60 output, (47/60)^1.3.

 

[GeddyMortgage]

thanks

As you will have sized the rads to give 30253 BTU, 8.87kw at T30 then this means they are sized to give 21.82kw, (8.87X2.46), at T60 so if you turned the boiler temp back up to 84c, the rad/boiler output will be 21.82kw.

Yes, you throttle down the lockshield valves.

You only need to heat the entire cylinder to 60C once per week. You can do this either manually or if your boiler is suitable you may be able to install Hot Water Priority where the CH is set to whatever temperature you require and when HW is required the boiler automatically changes the boiler setpoint to 80C and then reverts back once the HW cylinder is up to 60C.
If you leave the boiler at 70C then realistically as you can't get much lower than a rad dT of 6C then you have a T47 rad, (70+64)/2) minus 20, to give 73% of its T60 output, (47/60)^1.3.

Thanks - so in logistical terms, If I’ve calculated the current setup to be 38kw at T60.

If I drop it to 70C can I add some more rads?

Also I’ve tried it at 70c (about 3 o clock on the gauge) for the past hour or so. Two rads on the ground floor are decently hot, all the rest are id say somewhere between warm and hot. Maybe it’s what I’m used to but that doesn’t seem right?

Also worth mentioning about 6/7 rads have now been blanked off so I’d have expected the others to all be quite warm as only 15 rads left in the system on a 40 odd kw boiler.

Something doesn’t seem right?

 

[Johntheo5]

thanks


Thanks - so in logistical terms, If I’ve calculated the current setup to be 38kw at T60.

If I drop it to 70C can I add some more rads?

By calculation 38kw at T60 is 27.7kw (T47), so you can add 14.1kw (of T60) = 10.3kw (T47 at 70C).

Also I’ve tried it at 70c (about 3 o clock on the gauge) for the past hour or so. Two rads on the ground floor are decently hot, all the rest are id say somewhere between warm and hot. Maybe it’s what I’m used to but that doesn’t seem right?

Rads need balancing or/and pump speed/head increased.

Also worth mentioning about 6/7 rads have now been blanked off so I’d have expected the others to all be quite warm as only 15 rads left in the system on a 40 odd kw boiler.

As above, if the boiler flowtemp is 70C. What is the boiler return temp?, you may see it in one of the menus.

Something doesn’t seem right?