Note: We have two different technical guides related to radiators:
The main question any customer will have regarding central heating radiators is "What heat output in BTUs do I need for my room?". We have listed two different ways you can approach calculating this.
1. Calculating BTUs of Heat Output Required  Option 1 of 2  Use our Heat Loss Calculator.
View Geyser's highly advanced HEAT LOSS CALCULATOR using the very latest user interface.
2. Calculating BTUs of Heat Output Required  Option 2 of 2  Use Your Existing Panel Radiators as a Guide.
When your house was built, the contractor or builder will have spent time choosing the right radiators taking into account how the house was built. Therefore this is a good base on which to start. We often find people seeking to replace their standard panel radiators with designer radiators, so taking the output of the existing models makes perfect sense.
Measure the height and width of your existing radiator, then use the table below to find the type you have and determine its power output in BTUs. Remember if your existing radiators aren't warming your room efficiently, increase the heat output from the figures given below, for the replacement model you choose.
Single Panel

Length 

600mm 
900mm 
1200mm 
1500mm 
1800mm 


2ft 
3ft 
4ft 
5ft 
6ft 
Height 
300mm (12ins) 
1121 BTUs (t60)

1681 BTUs (t60)

2241 BTUs (t60)

2802 BTUs (t60)

3362 BTUs (t60)


450mm (18ins) 
1638 BTUs (t60)

2457 BTUs (t60)

3276 BTUs (t60)

4095 BTUs (t60)

4914 BTUs (t60)


600mm (24ins) 
2112 BTUs (t60)

3168 BTUs (t60)

4224 BTUs (t60)

4849 BTUs (t60)

6336 BTUs (t60)


750mm (30ins) 
2500 BTUs (t60)

3748 BTUs (t60)

5000 BTUs (t60)

6250 BTUs (t60)

7440 BTUs (t60)

Single Panel With Fins

Length 

600mm 
900mm 
1200mm 
1500mm 
1800mm 


2ft 
3ft 
4ft 
5ft 
6ft 
Height 
300mm (12ins) 
1595 BTUs (t60)

2392 BTUs (t60)

3190 BTUs (t60)

3987 BTUs (t60)

4784 BTUs (t60)


450mm (18ins) 
2414 BTUs (t60)

3621 BTUs (t60)

4827 BTUs (t60)

6034 BTUs (t60)

7241 BTUs (t60)


600mm (24ins) 
3103 BTUs (t60)

4655 BTUs (t60)

6207 BTUs (t60)

7758 BTUs (t60)

9310 BTUs (t60)


750mm (30ins) 
3707 BTUs (t60)

5560 BTUs (t60)

7414 BTUs (t60)

9267 BTUs (t60)

11120 BTUs (t60)

Double Panel

Length 

600mm 
900mm 
1200mm 
1500mm 
1800mm 


2ft 
3ft 
4ft 
5ft 
6ft 
Height 
300mm (12ins) 
1724 BTUs (t60)

2566 BTUs (t60)

3421 BTUs (t60)

4310 BTUs (t60)

5172 BTUs (t60)


450mm (18ins) 
2414 BTUs (t60)

3621 BTUs (t60)

3742 BTUs (t60)

6034 BTUs (t60)

7241 BTUs (t60)


600mm (24ins) 
3017 BTUs (t60)

4526 BTUs (t60)

5987 BTUs (t60)

7543 BTUs (t60)

9052 BTUs (t60)


750mm (30ins) 
3381 BTUs (t60)

5560 BTUs (t60)

7414 BTUs (t60)

9267 BTUs (t60)

11120 BTUs (t60)

Double Panel With Single Fin

Length 

600mm 
900mm 
1200mm 
1500mm 
1800mm 


2ft 
3ft 
4ft 
5ft 
6ft 
Height 
300mm (12ins) 
2500 BTUs (t60)

3750 BTUs (t60)

5000 BTUs (t60)

6250 BTUs (t60)

7500 BTUs (t60)


450mm (18ins) 
3707 BTUs (t60)

5560 BTUs (t60)

7414 BTUs (t60)

9267 BTUs (t60)

11120 BTUs (t60)


600mm (24ins) 
4741 BTUs (t60)

7112 BTUs (t60)

9483 BTUs (t60)

11853 BTUs (t60)

14223 BTUs (t60)


750mm (30ins) 
5517 BTUs (t60)

8276 BTUs (t60)

11034 BTUs (t60)

13793 BTUs (t60)

16551 BTUs (t60)

Double Panel With Double Fins

Length 

600mm 
900mm 
1200mm 
1500mm 
1800mm 


2ft 
3ft 
4ft 
5ft 
6ft 
Height 
300mm (12ins) 
3275 BTUs (t60)

4914 BTUs (t60)

6552 BTUs (t60)

8189 BTUs (t60)

9827 BTUs (t60)


450mm (18ins) 
4483 BTUs (t60)

6724 BTUs (t60)

8965 BTUs (t60)

11207 BTUs (t60)

13448 BTUs (t60)


600mm (24ins) 
5776 BTUs (t60)

8664 BTUs (t60)

11551 BTUs (t60)

14439 BTUs (t60)

17327 BTUs (t60)


750mm (30ins) 
6896 BTUs (t60)

10345 BTUs (t60)

13793 BTUs (t60)

17200 BTUs (t60)

20689 BTUs (t60)

3. The Two Different Scales for Specifying Heat Output are BTUs and Watts.
BTUS: Plumbers will often specify the heat output you'll need in BTUS and this figure will normally be in up in the 1000s.
BTU stands for British Thermal Units and is a basic measure of thermal energy, where 1 BTU is the amount of energy needed to heat 1 pound of water to 1 degree fahrenheit. The figures are so high when specifying BTUS for radiators as they are heating enough pounds of water to warm your whole room.
Watts: Sometimes plumbers will also specify heat output in kilowatts (which is equal to 1000 Watts). 1 watts of heat output is equal to 3.41 BTUS, so watts will always be the lower figure of the two scales. Typically electric radiators & electric heated towel rails are measured in watts, due to the fact they use electric as the energy source and electric is often referred to in watts.
4. How do you Convert Watts to BTUS (and vice versa)?
BTUS = Watts multiplied by 3.41, WATTS = BTUS divided by 3.41
5. What does 'Delta' mean and how does this affect the BTUs of a radiator?
All Geyser Heat Outputs are listed in Delta T60, as this is the typical unit used by British Plumbers. There are 3 Different Delta Outputs: T50, T60 and T70  which we have explained in the diagram below:
Want to Know More? To explain the concept of Delta in more detail all heat outputs have been obtained from controlled laboratory tests, using a standard installation criteria. From 1st July 1997 all radiators manufactured in Europe need to conform to the European standard BS EN442. Under this standard it is necessary to test radiators with a flow (inward) water temperature of 75 C and a return (outward) temperature of 65 C, in a test room with a consistent air temperature of 20 C. At a 75 C flow water temperature, and a 65 C return water temperature the mean average water temperature (MWT) is 70C. If we minus the room temperature of 20 C, we are left with a temperature differential of 50 C or a Delta T of 50.
6. IMPORTANT: Be mindful to check the Delta specified is the same when comparing Radiators from Different Suppliers?
Be mindful when comparing radiators across different suppliers to check the Delta given on the heat outputs, as this an falsify the heat outputs when comparing like for like products which have been given with different Delta heat outputs.
If it isn't specified (like it is on all of our products) you should ask the other supplier what Delta figure is used.
If you wish to convert our Delta T60 ratings, to give you a true indication as to heat output when comparing with other suppliers in different formats, use these formulas:
· T70 = T60 multiplied by 1.33 T70 = T50 multiplied by 1.4
· T50 = T60 divided by 1.264 T50 = T70 divided by 1.4
· T60 = T50 multiplied by 1.264 T60 = T70 divided by 1.33
7. What Aspects of a Radiator determine its Heat Output?
Firstly: Tube diameter is directly linked to the heat output, as the larger the tubes, the higher the holding capacity of the radiator and the greater the heat output. If you are looking for the highest heat output you can find, we suggest looking for the largest 'exhaust pipe' style tubes you can see, as these will emit the most heat bar for bar.
Secondly: Colour choice affects the heat output of a radiator. Any sparkling chrome radiator will give out slightly less heat output compared with a like for like model in a white, black or a brushed chrome finish. This is because the chrome plating will act as a form of insulation, thus allowing the radiator to retain more heat internally (just like tin foil wrapped around a joint in the oven). However a painted finish like white or black will permeate the heat much better.
8. Where is the Best Location to install my Radiator?
The ideal place for a raditaor to be located is on the outside wall and under or next to a window if possible. The cold air coming in through the window can then be mixed with the hot air coming coming up form the radiator, which then mixes together to create a nice ambient temperature.
