What Size Underfloor Heating System Do I Need?
Choosing the correct size is one of the most important parts of buying an underfloor heating system. Too small and the system may not provide enough heat for the room. Too large and you could end up purchasing more equipment than necessary. So, how do you work out what size underfloor heating system you need? The answer starts with understanding your actual heated floor area.
Don't Just Measure the Whole Room
The first mistake many people make is measuring the entire room and using that figure to choose their system. Underfloor heating is generally installed across the usable heated area, rather than beneath every part of the floor. Areas occupied by permanent fixtures and furniture may need to be excluded depending on the system. This is particularly important for electric heating mats and cables.
How Do You Calculate the Heated Area?
Start by measuring the length and width of the room. For a simple rectangular room:
Length × Width = Total Floor Area. You then need to deduct areas that won't be heated. These could include permanent fixtures or other areas specified by the heating system manufacturer. The result is your approximate heated area.
Why Is Correct Sizing Important?
Correct sizing ensures that the heating system is suitable for the room. If you choose a system that is too small, it may struggle to achieve the required temperature. If you choose too large a system, you may be paying for heating that isn't required. This is why accurate measurements are important before ordering.
What About Electric Underfloor Heating?
Electric underfloor heating systems are available in different outputs and coverage sizes. Fastwarm offers electric heating mats in different outputs, including 150W/m² and 200W/m² options for different applications. The appropriate output depends on the room and its heat-loss requirements. Its higher-output 200W/m² system is intended for areas with higher heat loss, such as conservatories and extensions.
What About Water Underfloor Heating?
Water underfloor heating is usually designed around the property rather than simply selecting a mat size. The design needs to consider:
- Room dimensions
- Heat loss
- Pipe spacing
- Floor construction
- Flow temperatures
- Heat source
- Heating zones
This is why larger water underfloor heating projects benefit from a bespoke system design.
Does Insulation Affect the System Size?
Yes. The insulation levels of the property can have a significant impact on heating requirements.
A well-insulated room generally requires less heat to maintain a comfortable temperature than a poorly insulated one. This is particularly important in:
- Extensions
- Conservatories
- Older properties
- Rooms with large windows
- Ground-floor rooms
Does Flooring Affect the Calculation?
Flooring can affect how efficiently heat transfers into the room. Tiles and stone are excellent conductors. Carpet, thick underlay and some wood products can provide greater thermal resistance. If you're planning to install carpet, engineered wood, LVT or laminate, check that the flooring is compatible with your chosen heating system.
Do I Need to Heat Under Kitchen Units?
Generally, permanent fixtures don't need to be included in the heated area. This is why it's important to create a floor plan before ordering your system. Mark out:
- Kitchen units
- Islands
- Baths
- Built-in wardrobes
- Permanent cupboards
- Other fixed furniture
This will help determine where heating is actually required.
What About Multiple Rooms?
If you're heating several rooms, don't simply add the floor areas together and assume one system will work. Each room may have different heating requirements. For water systems, rooms can often be divided into separate heating zones. This allows you to control temperatures independently. For example, your bathroom may need to be warmer than your bedroom.
Can Fastwarm Help Me Calculate the Correct Size?
Yes. Fastwarm offers a free bespoke design and quoting service for customers planning underfloor heating projects. Providing accurate floor plans and information about the property can help the team determine the appropriate system and components. This can be particularly helpful for larger projects where several rooms or different floor constructions are involved.
What Information Should You Have Ready?
When requesting a system design or quote, it can help to provide:
- Room dimensions
- Floor plans
- Flooring type
- Floor construction
- Property type
- Insulation information
- Existing heating system
- Number of rooms
- Preferred thermostat controls
The more information available, the easier it is to design a suitable system.
Choosing the right underfloor heating size isn't simply about measuring your room. You need to consider the actual heated area, insulation, flooring, room heat loss and the type of heating system you're installing. For simple single-room projects, calculating the heated area can be relatively straightforward. For larger installations, a bespoke design can give you greater confidence that you're ordering the right system.
Not sure what size underfloor heating system you need? Contact Fastwarm for a free bespoke design and quote, or explore the full range of electric and water underfloor heating systems.
