How to measure underfloor heating

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The cold weather is an enemy for many. Underfloor heating is a fantastic solution for keeping you warm and cosy during those lower temperatures. If you’ve opted for heated floors, great choice! First, you will need to measure for underfloor heating. Here’s how you can prepare for underfloor heating mats or loose cable kits to help keep your property well-heated for years to come.

Table of contents

• Underfloor heating mats vs loose cable kits
• Measuring methods for underfloor heating installation
  • First method
  • Second method (ideal for smaller areas)
  • Third method (ideal for areas with multiple furnishings)
  • Loose cable system

Underfloor heating mats vs loose cable kits

Mats and cable kits perform similarly but have key differences, including how their wattage output is affected. That’s why there are differences in their measuring techniques.

• A mat system’s output wattage is determined by the power of the cable per m2.
• Loose cable kits have an output wattage determined by the spacing between the cables.

Other key considerations are that the 150-watt and 200-watt mats have the same cable spacing, but the 200-watt mat will have a cable with more power. For loose cable kits, minimum and maximum spacing is important to prevent hot and cold spots.

Regardless of which heating system you choose, it’s better to have a little less cable than leftover cable. Excess cable won’t work when typically cut by the installing party. So, purchasing a smaller mat is advised in this instance.

Measuring methods for underfloor heating installation

To measure the maximum heated area of your room, you can use any of these three common methods.

The first method

This is the most common method for measuring for underfloor heating installation.

Step one: Measure (in metres) the total floor area of the room in which the underfloor heating will be used.

Length x width = total floor area in m 2

Step two: Identify areas that will be non-heated. For example, areas of the room with permanent fittings such as toilets, sinks and baths.

Step three: Remove the total for the non-heated floor area from the total floor area.

Total floor area – total non-heated floor area = new total floor area

Step four: Reduce the new total floor area result by 10%, then round it to the nearest heating mat size available.

Why remove 10% from the total? The 10% is removed to allow for gaps around the edges of your heating installation. When you install the boards, these can then be fitted flush to the walls of the room. So you needn’t worry about each section of underfloor heating, while still maintaining gaps between them.

The second method (ideal for smaller areas)

If you have a smaller space to measure, this method is more suited to you.

Step one: Minus 100mm from the length and width of the room, then identify the total floor area. Make sure this is done in metres.

Length of room – 100mm = new total length of the room

Width of room – 100mm = new total length of the room

Length x width = total floor area in m 2

Step two: Identify areas that will not be heated. For example, areas of the room with permanent fittings such as toilets, sinks and baths.

Step three: Remove the total for the non-heated floor area from the total floor area.

Total floor area – total non-heated floor area = new total floor area

Step four: Round the new total floor area to the nearest heating mat size available.

The third method (ideal for areas with multiple furnishings)

If your room has many obstacles, this method works well around them.

Step one: Separate the floor area into zones of smaller rectangular or square spaces to work with and measure (in metres) these sections to find the total of each area. Then add these totals together for a complete area total.

Zone one total + zone two total + zone three total = total floor area

Step two: Identify areas that will not be heated. This includes areas covered by bathroom storage units and other similar furnishings that are permanent fixtures.

Step three: Remove the total for the non-heated floor area from the total floor area.

Total floor area – total non-heated floor area = new total floor area

Step four: Reduce the new total floor area result by 10%, then round it to the nearest heating mat size available.

Removing 10% allows for gaps around the edges of your heating installation. When installing the boards, fit them flush to the walls of the room. Minimising worry about each section of underfloor heating while still maintaining gaps between them.

Each of the methods mentioned above can be used to help learn about underfloor heating measurements. However, if you prefer loose cable systems, then view the method below.

Loose cable system

Many professionals use loose wire underfloor heating kits in areas where space is tight or cluttered. It can take longer and more effort for installation in terms of parts and planning. However, this option works well if you need a system that fits around obstacles, as long as you maintain the manufacturer’s recommended minimum cable spacing.

With that, here’s how to measure for a loose cable heating system.

Step one: Choose one of the three methods mentioned above, below ‘Measuring methods for underfloor heating installation’. Once you’ve chosen a method, calculate the maximum heated area for the room.

Step two: Select the wattage required for the underfloor heating to output (See tables below). This determines how much space you need between the loose cables and the total cable length required to cover the area and achieve the desired wattage.

Note: Loose cable kits are manufactured and marketed based on 200 watts per m2 at a 200mm spacing. The higher the wattage, the quicker the floor will reach the desired temperature and vice versa.

200 watts

175 watts

150 watts

135 watts

Step three: Once you’ve chosen your wattage, use the table to see what space and cable length you need for your underfloor heating area. Then, purchase the kit that matches your chosen wattage.

These are your methods for measuring underfloor heating with mats or an electric underfloor heating loose cable kit! However, do seek professional support if you are uncertain about your measurements or loose cable system requirements.

Want to find out more about underfloor heating? Maybe you need to know how to bleed existing underfloor heating or ensure you can repair and maintain underfloor heating in future. Check out our wide range of Help and Advice for more information.