Use this guide to quickly calculate the required radiator size for a given room such as a bedroom, kitchen, bathroom, living or dining room etc.

This process is incredibly easy and will only take you five minutes.

This guide is perfect for:

• Homebuilders
• Those constructing a loft, side extension or new basement
• Homeowners who want to see if their existing boiler is suitable for the number of rads in the home
• Those who may feel a given radiator is too small for the room size

Some inexperienced or lazy radiator installers just fit a radiator that is too big and then fit thermostatic valves so the occupant can adjust the temperature as required.

This isn’t a good practice as errors could lead to a small radiator being fitted or too much space being wasted if an overly large one is chosen.

Also, some occupants won’t adjust the thermostatic radiator valve and will just switch the heating on and off as required, this isn’t the most efficient way to operate a central heating system and will cost the bill payer more money in the long run.

Use a BTU Calculator For Radiator Sizing

Radiator output is measured in BTUs, so you need to calculate the required BTU for each room in your home.

The easiest way to check the radiator sizing for your home is to use a BTU calculator.

BTU stands for British Thermal Unit and is a standard way to measure the heat output of a radiator.

In mainland Europe, they use wattage but here in the UK, we like to be different, and both measurements are used.

To use a BTU calculator, you will need the following information:

• Width, height and length of each room in the home (in metres)
• Type of windows, single or double glazed etc
• Thickness of the external walls; single or double skin etc
• Insulation between the two walls (cavity) and depth of insulation in the loft
• What is located below and above each room, i.e. another room, an attic or a concrete floor etc

Don’t worry if you don’t have all the details, just assume a worst-case scenario and the calculator will suggest a radiator size slightly larger than you need.

While there are tons of BTU calculators on the web, we feel that this is the best one.

Do The Math

Once you have created a BTU calculation for each room in your home, you’ll know the exact power output of each radiator you need.

All radiators are advertised with BTU output information,  this makes it easy for you to select the correct product:

Typical radiator specifications chart

It’s unlikely that you’ll find radiators that match exactly your home’s requirements so just select the next size up.

It really is that simple!

An Example – Two Bed Home

Below is an example based on a two-bed property I recently worked on:

Get started with the BTU calculator here.

Tips to Improve Radiator Efficiency

Follow these best practices to ensure you get the most from your central heating system:

• If your system is old and the radiators have cold spots even after bleeding the air out, consider a power flush
• Don’t place large pieces of furniture in front of radiators
• Avoid draping curtains in front of the radiators
• If you have old drafty windows (not modern double glazed units), then you must place the radiator below the window to create a wall of warm air that keeps out the cold. This isn’t necessary with modern window frames and glass, so if you have double/triple glazing, you can be more creative with your radiator locations
• Fit thermostatic valves so you can adjust the temperature in each room as required. I have the spare bedroom and downstairs toilet in my home kept at a low setting to conserve energy
• Is the room longer than 6 metres? You should install two smaller radiators instead of a single larger one; this will ensure your system distributes the heat evenly
• Make sure your radiators are balanced correctly

What is the going rate for a plumber to install a new radiator? Check out our price guide here.

Don’t Want to do This Project Yourself?

Our select partner can provide you with a quote for radiator purchase, installation and much more including a complete central heating system.

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