Radiator sizing

[rob_j20]

I'm about to start fitting the first of some new radiators, i think i get most of it.

So far i have used this calculator. http://www.theradiatorcompany.co.uk/heatoutput/

4.140 x 2.970 x 2.440 with a large window.

This gives me an upper figure of 5275 BTU (1546kw) for the room in question. Now i understand this is based on a delta t50, but with wanting a combi it would most likely be around t40, or even 30 if i can run the boiler that way, aim for a 20c drop in temp. 70/50/20, or 60/40/20 if it will go that low.

What calculation do i need to convert to different delta t?

 

[D_Hailsham]

This should help.

To apply the factors shown in the table below to the quoted outputs, multiply the quoted output by the chosen operating factor to give new output. E.g a nominal 1kw radiator with a ΔT of 40C will produce 1000 x 0.748 =748W.

To apply the factor to required output, divide required output by factor to give correct radiator size. e.g to produce 1kW with a ΔT of 40C you will have to install a 1000 ÷ 0.748 = 1337W radiator, or the nearest larger.

ΔT is the difference between mean water temperature and room temperature in °C The table shows the factors for ΔT other than 50°C.

ΔT - Factor
10 - 0.057
10 - 0.123
15 - 0.209
20 - 0.304
25 - 0.406
30 - 0.515
35 - 0.629
40 - 0.748
45 - 0.872
50 - 1.000
55 - 1.132
60 - 1.267
65 - 1.406
70 - 1.549
75 - 1.694

 

[rob_j20]

Great just what i was after, looks like the room needs around 3kw at delta t30 or 2kw at 40. Makes a big difference.

 

[D_Hailsham]

So far i have used this calculator. http://www.theradiatorcompany.co.uk/heatoutput/

The methodology used for that calculator is suspect. Use this Radiator Calculator instead.

 

[D_Hailsham]

Looks like the room needs around 3kw at delta t30 or 2kw at 40. Makes a big difference.

Not strictly correct. The room needs 1546W (not 1546kW as in your opening post!!). But you will have to install a rad with a nominal output of 2kW or 3kW, depending on ΔT, to achieve the required output.