BTU Calculator For Radiator – All You Need To Know | Checkatrade
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BTU calculator for radiator

When installing or replacing radiators, it’s important to know what heat capacity you need for the spaces you’ll be heating. In this guide, we look at what a BTU calculator for radiator is and why it can be very handy for planning your heating.

When installing or replacing radiators, it’s important to know what heat capacity you need for the spaces you’ll be heating. In this guide, we look at what a BTU calculator for a radiator is and why it can be very handy for planning your heating.

Whether you’re building a new home, working on an extension, or simply upgrading the heating system in your existing home, keep reading to find out more about a BTU radiator calculator.

What is a radiator BTU calculator?

A radiator BTU calculator, or heat output calculator, is a tool used to work out how much radiator power you need to heat a space. A radiator calculator will typically take into account a number of factors that will affect the heat output needed, such as the dimensions of the room, heating levels and types of windows present (if any).

The calculator will then provide a result that tells you how much radiator power you need. In larger rooms and spaces it’s quite common that multiple radiators will be needed to produce the required heat output.

If you’re looking to find out how much upgrading your radiators it will cost, take a look at our guide about the cost to remove and replace a radiator.

What does BTU mean?

BTU, otherwise known as British Thermal Units, is a unit of measurement for energy typically used when referring to heating – and more specifically radiators. 1 BTU represents the amount of energy needed to raise the temperature of 1 pound of water by 1-degree Fahrenheit.

The higher the BTU number, the higher the heating power – meaning a higher BTU radiator will be able to heat a smaller space more quickly than a lower BTU radiator, or warm a bigger space in the same amount of time.

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Radiator calculator

Radiator on orange wall

In order to calculate a basic estimate of the BTU heat output needed for a room, you can measure the dimensions of the room and walls. For a more accurate measurement you’ll need to factor in the following:

  • Room dimensions including ceiling height
  • Number of windows in the room
  • Size of windows
  • Type of window and/or glazing (single or double)
  • Number of walls on the outside of the building
  • Outside wall material
  • What is above and below the room
  • The temperature that you want to heat the room to

Central heating radiator calculator

When it comes to a radiator room size calculator, there’s a manual calculation you can do that will help you reach a pretty accurate figure. Follow these steps:

Step 1 – Measure the volume of the room in cubic feet

Step 2 – Multiply the cubic feet by the following

  • Lounges and dining rooms – multiply cubic feet 5
  • Bedrooms – multiply cubic feet by 4
  • Common areas and kitchens – multiply cubic feet by 3

Step 3 – Factor in any additional heat loss

  • Room facing North – add 15%
  • French windows – Add 20%
  • Double glazing – Deduct 10%

Step 4 – The result

The above radiator BTU calculator will provide you with an estimated heat output that you’ll need for each room. These calculations are approximate, so for an accurate measurement, we recommend contacting your local radiator specialists to provide more detailed recommendations.

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Why do I need a BTU radiator size calculator?

Being able to sufficiently heat your home requires understanding how much heating each room requires, and that’s where the BTU radiator size calculator comes in. By helping you identify the heat output that you need from your radiators, you can ensure that you install or upgrade the right size radiators for each room in your home.

Radiator heating a living roomIf you choose a radiator that’s too weak for the space it’s trying to heat, the room will never reach the temperature you want. And if you install a radiator that’s too powerful, you’ll end up spending more on your energy bills than you need to.

Find out if your existing radiators are sufficient by using a BTU calculator, or contact a local radiator expert to do it for you.

How do I choose the right size radiator?

Once you know how many BTUs you’ll need to heat a room, you can choose the radiators that will be able to provide that level of heating. If it’s a large room then you can combine two or more radiators to achieve the BTU level needed.

If in doubt, enlist the professional advice of a plumber to help you both calculate the BTU requirements for your home and offer recommendations for the best radiator(s) for you to choose. To find out about prices, check out our guide to plumber costs.


How do I calculate the BTU for my room?

Using the above BTU calculator for your radiator needs is a good first step. Think of it as a ‘what size radiator do I need for my room calculator’. That said, the best way to get an accurate calculation is to speak to a plumber, who will be able to calculate your radiator BTU needs.

How is a room’s BTU value calculated?

To calculate the BTU requirements of a room you need to start with the cubic volume of the space (height, width and length), multiply it by 4 as an average and consider any heat loss factors (+15% for rooms facing North, +20% for French windows, and -10% for double glazing).

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