Welcome back to UKAA

Please enter your email address and password below.

Register with UKAA

Please enter your email address and password below.

UK Architectural Antiques. Suppliers of cast iron radiators and interiors



During this unimaginable time in the world's history. UKAA can be contacted by telephone or email.
Our business premises are closed to customers; however, you can purchase online through our website.
We want to offer continual product support to our existing customers.
We want to offer advice, guidance and quotes to prospective new customers.
To do this Viv is available  01543 222 923 from 9am-11am Monday-Friday.
We are also available to give you a call back at a time to suit you please do email us info@ukaa.com

* Excluding VAT & Delivery

Cast Iron Radiator BTU calculator

A BTU calculator for radiators, also known as a BTU radiator calculator or radiator size calculator, is used to measure the amount of heat required for any specific room in your house, in terms of British thermal units (BTUs). Our Cast Iron radiator BTU calculator will work out how much energy and what sized radiator you will need, based on the measurements that you provide.

To calculate the total cast iron radiator heat output required for your room (BTU/hour), simply complete the following form:

1. Select units:
2. Enter your room dimensions
Width: (feet)   Length: (feet)   Height: (feet)
3. (Optional) Specify the maximum height of radiator you can accomodate in you room:

Maximum Height: (mm)
4. Select your room type:

5. Additional features:
6. The size of your cast iron radiator (the number of sections required) is based on:



Important Notes about Delta Δ calcuations


*Delta 60 covers the majority of standard central heating systems.

For the vast majority of our customers using standard central heating systems, we use Delta 60. For systems such as ground source heat pumps, a lower Delta 50 may be required. Please consult your heat source supplier for more information.

Please do not hesitate to call us on  01543 222 923 if you require any further information.

At 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, and we’ve made the choice much easier with our easy to use 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 are 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 Room BTU calculator.

Our BTU calculator is designed to ensure that your Cast Iron Radiators will sufficiently heat the room they are installed within.

How To Calculate BTU

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 BTU requirements for that room, you can now work out how many ‘sections’ of your style of radiator are required to give you that radiator output.

Most online BTU calculators are very similar, but the main thing to watch out for is that the cast iron 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.

If you have any problems trying to calculate BTU on your radiators, then please do not hesitate to.

Calculating Ouptut Needed For Awkward Shaped Rooms

Please see this simple step by step guide on how to calculate BTUS for an awkward shape room.

If your room is not a square/rectangle shape we recommend measuring like below and splitting the rooms into sections:

Awkward Shape Room how to Calculate BTU

Then work out the required 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 then 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:

Awkward Shape Room how to Calculate Heat Needed

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

Calculate the output needed for each section.

Then section 1s - 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.

For more information or help please do contact us at the office on 01543 222923.

The BTU calculator might recommend a large cast iron radiator

Click Here To Build Your Bespoke Cast Iron Radiators

Your radiator heat output might recommend you have a smaller radiator

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