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

[GeddyMortgage]

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

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

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

Thanks again - I’ll take a look at the return temp if it’s possible to see it in a config menu shortly.

If I add that many rads then put it back to full temp though, in real life terms what will happen? Boiler damage?

 

[Johntheo5]

No boiler damage, its designed to run with a maximum fuel/heat input, if the rad demand is greater than the boiler output then the boiler flow temp will fall and the rad output will fall until both are in balance.

 

[JonathanM]

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

I've just been checking the radiator outputs from the main manufacturers. From a first look, it seems that your BTU estimates are much closer to T50 outputs than T60 outputs. Can I just check how you worked these out. I think you mentioned an online calculator?

 

[GeddyMortgage]

I've just been checking the radiator outputs from the main manufacturers. From a first look, it seems that your BTU estimates are much closer to T50 outputs than T60 outputs. Can I just check how you worked these out. I think you mentioned an online calculator?

very Interesting, and thanks so much for looking into it for me, I used a couple of calculators, to be fair one of them said it was based on T60 one said T50 and the outputs came out the same...so I thought it was likely either one of them was wrongly titled. I'll put the links of the calculators I used below. (First one looks like it used t50, second looks like it used t60)

Panel Radiator Output Calculator - Castrads

www.castrads.com

Cast Iron Radiators Ltd

function supports html5 storage {try{returnlocalStoragein window window localStorage null}catch e {return 1}}var CalcApp new function {this base

www.castironradiators.ltd.uk

 

[GeddyMortgage]

No boiler damage, its designed to run with a maximum fuel/heat input, if the rad demand is greater than the boiler output then the boiler flow temp will fall and the rad output will fall until both are in balance.

Thanks for explaining that. I have a potentially silly question about the inverse of that.

Looking into zoning the property, for simplicity of maths lets say of the 24 rads that currently come on when I turn the boiler on, Lets say If I split it into 2 zones, (Zone 1 = 12 rads Downstairs, Zone 2 = 12 rads Upstairs)

If I set the boiler to MAX but only had Zone 1 Active, as there'd be far fewer rads to power...would that cost me less £ per hour to run the boiler than it currently does when on MAX and feeding all 24 radiators? or does it not work like that? and the boiler just costs the same regardless of how many rads it's feeding?

 

[Johntheo5]

very Interesting, and thanks so much for looking into it for me, I used a couple of calculators, to be fair one of them said it was based on T60 one said T50 and the outputs came out the same...so I thought it was likely either one of them was wrongly titled. I'll put the links of the calculators I used below. (First one looks like it used t50, second looks like it used t60)

Panel Radiator Output Calculator - Castrads

www.castrads.com

Cast Iron Radiators Ltd

function supports html5 storage {try{returnlocalStoragein window window localStorage null}catch e {return 1}}var CalcApp new function {this base

www.castironradiators.ltd.uk

I just compared one at T50 vs T60 (above) and the T60 doess reflect its greater output of 26.7%,, (60/50^1.3.

 

[Johntheo5]

Thanks for explaining that. I have a potentially silly question about the inverse of that.

Looking into zoning the property, for simplicity of maths lets say of the 24 rads that currently come on when I turn the boiler on, Lets say If I split it into 2 zones, (Zone 1 = 12 rads Downstairs, Zone 2 = 12 rads Upstairs)

If I set the boiler to MAX but only had Zone 1 Active, as there'd be far fewer rads to power...would that cost me less £ per hour to run the boiler than it currently does when on MAX and feeding all 24 radiators? or does it not work like that? and the boiler just costs the same regardless of how many rads it's feeding?

The boiler will modulate to exactly match the rad demand, if the rad(s) demand is say 30kw with both zones on then the boiler will output 30kw if its 15kw with one zone on, it will output 15kw.

 

[GeddyMortgage]

The boiler will modulate to exactly match the rad demand, if the rad(s) demand is say 30kw with both zones on then the boiler will output 30kw if its 15kw with one zone on, it will output 15kw.

So in theory you can never buy a boiler that's "too big"?..... Do i need to run it efficiently for it to be able to modulate down like that? or can I still run it on MAX and see it modulate down?

And...(again sorry if stupid question)..... Instead of Zoning, if I just went and turned 12 of the Rads off at their thermostatic valves....that would have exactly the same effect as zoning? albeit a much more granular method of achieving the same thing?

 

[Johntheo5]

So in theory you can never buy a boiler that's "too big"?..... Do i need to run it efficiently for it to be able to modulate down like that? or can I still run it on MAX and see it modulate down?

You can let it set to max and it will modulate down, combi boilers are generally oversized for CH because they are sized for DHW demand and high flowrates. you might have a 45kw combi but only require 20kw CH demand max, again no problem in modulating down to a minimum of say 8kw but with greater insulation, zoning etc then the CH demand may be as low as 4 or 5kw so that boiler will start cycling as it can't modulate below 8kw so a small loss of efficiency.

And...(again sorry if stupid question)..... Instead of Zoning, if I just went and turned 12 of the Rads off at their thermostatic valves....that would have exactly the same effect as zoning? albeit a much more granular method of achieving the same thing?

Yes.

 

[GeddyMortgage]

You can let it set to max and it will modulate down, combi boilers are generally oversized for CH because they are sized for DHW demand and high flowrates. you might have a 45kw combi but only require 20kw CH demand max, again no problem in modulating down to a minimum of say 8kw but with greater insulation, zoning etc then the CH demand may be as low as 4 or 5kw so that boiler will start cycling as it can't modulate below 8kw so a small loss of efficiency.

I see....and that's the same in the case of a conventional CH only boiler like mine? (not a combi)

 

[Johntheo5]

Yes, you will see its min output in the manual but I wouldn't get too hung up about cycling, most of the these smart heating systems like Evohome and Drayton Weiser etc continually cycle the boiler to get very tight room temperature control and everyone seems happy.

 

[GeddyMortgage]

Yes, you will see its min output in the manual but I wouldn't get too hung up about cycling, most of the these smart heating systems like Evohome and Drayton Weiser etc continually cycle the boiler to get very tight room temperature control and everyone seems happy.

Good to know, we were umming and ahhing about the work required to have the zoning implemented, alternative was to use those HIVE thermostats on each rad.

But due to the length of the runs from the boiler to the ground floor and the fact that we had to have it piping hot flow, I think we’re leaning more towards just having a second boiler installed on the ground floor, likely a system boiler. That would then be responsible for heating the rads on the ground floor of which there’d be 10-12 (mainly type 22 /21)

The original boiler in the loft would then solely central heat the upstairs (10 rads).. and hot water tank.

It felt all things considered this would give each boiler a bit of head room…. And especially if the loft one will then modulate down if it’s then solely serving the 10 rads in the upstairs rooms.

Downsides - twice as many boilers to service… and the upfront install cost. But we’ve got the space atleast and means I could add a few rads to the ground floor if I need to.

 

[GeddyMortgage]

The boiler will modulate to exactly match the rad demand, if the rad(s) demand is say 30kw with both zones on then the boiler will output 30kw if its 15kw with one zone on, it will output 15kw.

Quick one on this, did a measure of hourly usage earlier, it didnt add up to what I thought it would in light of your advice, and it's left me a bit confused.

In early Jan I wanted to see how much M3 the boiler was using per hour when running the Central Heating, I measured it was using about 3.5M3 per hour (38.5kw/hr -ish?)..between then and now we've blanked off 5 radiators as part of the renovations.... but..... I measured it today and we're it's still using about 3.1M3per hour (33kw/hr-ish?).

With a good 25% of the rads now not in the circuit i'd have expected it to drop much further than that reading from Jan? Could this mean there's a problem somewhere or does this amount of difference seem normal?

I ask because my plan to either zone or go with a diff rad... i'd hoped that if this boiler was running half the rads it was originally, it'd essentially half my KW usage per hour, and half the cost to run it.

Have I missed something really obvious here and being stupid?

 

[Johntheo5]

In early Jan I wanted to see how much M3 the boiler was using per hour when running the Central Heating, I measured it was using about 3.5M3 per hour (38.5kw/hr -ish?)..between then and now we've blanked off 5 radiators as part of the renovations.... but..... I measured it today and we're it's still using about 3.1M3per hour (33kw/hr-ish?).

Boiler was probably running flat out and the flow temp had fallen so rads not giving their full T50 (or T60) output.

All I can state with certainty is that the fuel consumption is pro rata to the rad output, there will be a few % differences due to boiler efficiency changes but thats all.

With a good 25% of the rads now not in the circuit i'd have expected it to drop much further than that reading from Jan? Could this mean there's a problem somewhere or does this amount of difference seem normal?

I ask because my plan to either zone or go with a diff rad... i'd hoped that if this boiler was running half the rads it was originally, it'd essentially half my KW usage per hour, and half the cost to run it.

I would look regularly at the boiler return temperature, it will be in one of the menus, this is the single most important factor for high boiler efficiencies.

 

[DP]

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.

Unlikely boiler will be condensing other than when it starts up from cold