How to use a BTU Calculator

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How to use a BTU Calculator

A BTU (British Thermal Unit) Calculator or Heat Output Calculator is a really useful tool when choosing a traditional radiator for your period property. A BTU Calculator helps calculates how many BTUs are required to heat a given space or location and therefore helps determine the right sized radiator for that location. A Heat Output Calculator is exactly the same thing measuring the Heat Output required to heat your rooms.

What are the variables when using your Heat Output Calculator?

The BTU requirements of a room are determined by a number of variables. These include:

  • The number of external walls that the room has
  • The type of floor
  • The size of the windows
  • What is above and below the room
  • Whether windows are double glazed
  • Ceiling height
  • Size of the room
  • Type of wall insulation if any

When using a BTU or Heat Output calculator, simply enter the answers to the questions into the boxes provided to determine the BTUs of the radiator you need for each of your rooms. This will vary from room type to room type.

For example a small room with one external wall, i.e. a cloakroom, will have much lower BTU requirements than a lounge on the end of the house with two external walls and three windows.

Some other factors that can improve heat efficiency are:

  • Insulation under flooring will help the room to retain heat
  • Using blinds as well as curtains for large windows will prevent heat loss
  • Cellars are cheap rooms to heat as underground rooms help maintain a constant temperature
  • In period houses where wood windows are in tact but are not double glazed, draft excluder tape is a cheap and easy way to help prevent heat loss.

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Our Radiator Chooser goes a step further than a simple BTU or Heat Output calculator. As well as giving you the results of your BTU calculation, it will also list the styles of radiators from our selection, including our Victorian cast iron radiators and simple column style, that are suitable for your particular use. Most of the styles can be made to a wide variety of BTU requirements but any especially high requirements are best met with a radiator with an increased number of columns (so the depth will be greater) so that the width of the radiator isn’t too ungainly.

Radiator BTU Calculator


For any further assistance in using a BTU Calculator, please contact The Victorian Emporium and we will be pleased to help you. You can read our ultimate guide to period property renovation here.


Categories: Heating   Tags: cast iron radiators, radiators