Cast Iron Radiator BTU Calculator

Frequently asked questions

Why should I calculate radiator heat outputs?

UKAA, we are dedicated to finding the right cast iron radiators for you. It is important that you choose the right radiator for your desired room, which is why we’ve made the choice much easier with our simple cast iron radiator BTU calculator.

Each room in your property will require a certain amount of heat to keep that room warm. The radiator heat output required for the room can be expressed in British Thermal Units (BTU) or Watts. All styles of cast iron radiator emit different amounts of heat based on their size and the radiator’s output. If you’re considering buying a radiator, the first thing to do is to calculate the amount of BTU that is required for each room. The best way to do this is use a radiator power calculator.

Our radiator BTU calculator is designed to ensure that your radiators will sufficiently heat the room they are installed in.

How do I size a cast iron radiator with a BTU calculator?

To calculate the BTU formula for your room you will need to:

1. Enter the width, length and height of the room
2. Select your room type:
   • Lounge / Dining Room / Bathroom
   • Bedroom
   • Kitchen / common area
3. Answer three additional features:
   • Is your room north facing?
   • Does your room have a Patio Door?
   • Does your room have double glazing?

Now that you have calculated the requirements of the room, you can work out how many ‘sections’ of your radiator are required to give you the correct radiator output.

Most online radiator BTU calculators are very similar, but the main thing to watch out for is that the radiators that you buy are rated to British Standards. If you buy cast iron radiators that are tested to BS EN442-1 & BS EN442-2 – then you can be assured that the output of the Radiator is guaranteed. You don’t want to buy a radiator only to find that your rooms do not get warm enough!

At UKAA, we only sell British Standard tested radiators, so you can be safe in the knowledge that you are buying a high-quality radiator.

How do I calculate radiator heat outputs for awkward shaped rooms?

Please see this simple step by step guide on how to calculate BTU for an awkward shaped room. If your room isn’t a square/rectangle shape, we recommend measuring using the system below and splitting the rooms into sections - then work out the required BTU for each section using the online calculator.

For example:
Section 1 – 3m long x 4m wide x 2.8m tall
Section 2 – 3.5m long x 3.8m wide x 2.8m tall
Section 3 – 6m long x 8m wide x 2.8m tall

This will give you the required outputs that are needed for each part of the room. You can then add them altogether to give you the total requirement.

If your room has a vaulted/apex ceiling, we recommend you split the ceiling into two sections like below:

• Measure the height of each ceiling and treat each section as separate rooms e.g.

Section 1 – 4m long x 3.5m wide x 1.8m tall (you will need to measure the vaulted/apex ceiling at the highest point)
Section 2 – 4m long x 3.5m wide x 2.4m tall

Next, calculate the output needed for each section.

Then with section 1 - the requirement for the apex/vaulted ceiling will need to be halved. For example, if section 1 worked out to 4300 BTUs, halve it - so section 1 would then require 2150.

 

Add this figure onto section 2 this will then give you the total heating out needed to sufficiently heat the room.

 

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Now you know how to calculate BTU for your radiators, browse our selection of cast iron radiators online.