What radiator do I need?

The type of radiator you need will be down to your home heating needs and your taste or choice of style. You may be looking for a simple white radiator or you may want something to compliment the style of your home a bit more. You will also need to ensure your radiator is the right size for your home. We recommend that you speak with the relevant qualified trades person before purchasing. 

If you are looking to replace the radiators in your property or are keen to add new radiators to a new build property, then you will need to establish what level of heating output will satisfy the demands of each property. 

The heating output of a radiator is measured in BTUs (British Thermo Units) per hour. Larger rooms will require a higher heating output than smaller rooms as there is a larger area to heat. As a general rule this also means that larger radiators tend to have larger BTU outputs, although the panel style does play a part in this too. 

Factors such as the type of flooring, insulation and wall space can also have a huge bearing on the amount of heat that needs to be applied to a room to ensure it benefits from the warmth that the radiator emits. 

To make it easier for you to establish what level of radiator BTU you should be looking for, we have put together this quick and easy guide to our BTU calculator. 

We would like to stress that the below information is for guidance only and that if in any doubt at all you should consult a qualified heating engineer who will be able to tell you exactly what level of BTU output you should be looking for when buying a new radiator. 

Task 1 – How Big Is Your Room? 

The first thing you need to do is establish the volume of the room that you will be adding your new radiator to. This can be calculated using the following formula: 

Length of room (m) x Width of room (m) x Height of room (m) 

This will then give you the volume of your property (in m3) and essentially dictates the amount of space that needs to be heated within that room by your radiator(s).

Task 2 – BTU Calculator 

Having successfully established the volume of the room you want to install your new radiator(s) in, the next step is to work out the standard level of heating output (in BTU’s) required to heat a room of that size. 

This can be calculated using the following formula:  

Room volume (m3) x 153

Task 3 – What other factors play a part? 

Having carried out task 2 you should now know the BTU output required for your desired room size. Unfortunately, there are several other influential factors can play a part in increasing or decreasing the required BTU output for the room. For example, if you do not have any loft insulation in your property, then you can expect to require a radiator with a little more BTU output than previously specified. 

To take these factors into account we recommend that you work out if you need to take or add to the BTU output number you established in task 2. 

Here are some of the main factors that may influence this BTU figure: 

Factor 

Instruction 

For solid floor 

-10% 

For un-insulated cavity walls 

+10% 

For foam filled cavity walls 

-20% 

For upstairs bedrooms 

-25% 

For double glazing 

-5% 

For two outside wall 

+15% 

For three outside walls 

+40% 

For northern aspects 

+10% 

For no loft insulation 

+15% 

For high ceiling - 3m 

+20% 

Task 4 – What radiator size is needed? 

The following table gives you’re a rough understanding as to what size radiator you are looking at to reach your desired BTU output. 

Obviously the larger the radiator, the larger the heating output (BTU). Sadly, it is not as easy as just choosing the radiator size that you need – space is obviously a massive consideration in any radiator replacement job. It is therefore worth considering the different panel style options, with single panel single convector, double panel single convector and double panel double convector radiators all available and offering different levels of heat output despite holding the same radiator dimensions. 

The table below is a good guide to follow to gain an understanding about the type of radiator you should be looking for. If you need any further information about the radiator that is best suited for your room then we recommend contacting a qualified heating engineer. 

Single panel single convector

Double panel double convector

Height (mm) 

Width (mm) 

BTU 

Height (mm) 

Width (mm) 

BTU 

400 

600 

1356 

 

 

 

400 

900 

2033 

 

 

 

400 

1200 

2711 

 

 

 

500 

400 

1066 

500 

400 

2078 

500 

500 

1333 

500 

500 

2597 

500 

600 

1599 

500 

600 

3117 

500 

700 

1866 

500 

700 

3636 

500 

800 

2132 

500 

800 

4156 

500 

900 

2399 

500 

900 

4675 

500 

1000 

2666 

500 

1000 

5195 

500 

1100 

2932 

500 

1100 

5714 

500 

1200 

3199 

500 

1200 

6234 

500 

1400 

3732 

500 

1400 

7272 

500 

1600 

4265 

500 

1600 

8311 

600 

400 

1297 

600 

400 

2497 

600 

500 

1584 

600 

500 

3121 

600 

600 

1900 

600 

600 

3745 

600 

700 

2217 

600 

700 

4370 

600 

800 

2534 

600 

800 

4994 

600 

900 

2851 

600 

900 

5618 

600 

1000 

3167 

600 

1000 

6242 

600 

1100 

3484 

600 

1100 

6867 

600 

1200 

3801 

600 

1200 

7491 

600 

1400 

4434 

600 

1400 

8739 

600 

1600 

5068 

600 

1600 

9988 

700 

400 

1421 

700 

400 

2635 

700 

500 

1776 

700 

500 

3294 

700 

600 

2132 

700 

600 

3952 

700 

700 

2487 

700 

700 

4611 

700 

800 

3842 

700 

800 

5270 

700 

900 

3198 

700 

900 

5928 

700 

1000 

3553 

700 

1000 

6587 

700 

1100 

3908 

700 

1100 

7246 

700 

1200 

4264 

700 

1200 

7905 

700 

1400 

4974 

700 

1400 

9222 

700 

1600 

5685 

700 

1600 

10539 

 

At Direct Heating Supplies we have a large range of radiators available for you to purchase. You can view our radiators here and when you purchase today you are guaranteed excellent customer service and great prices. 

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