Heat Loss Calculations

What is a heat loss calculation?
A professional heat loss calculation forms the foundations to build an efficient heating system, without a heat loss calculation everything else is just a guess.

When a temperature difference exists between inside and outside heat will move, hot will always move towards cold. If your home is 21°C inside and the outdoor temperature is 10°C your heat loss is less, and heat will travel more slowly. When we experience cold weather such as -3°C your heat loss is greater, and heat will travel faster.

Every building material has a specific U-value which measures the rate of heat transfer through it which lets us know how effective the material is as an insulator, the lower the U-value, the better it is at keeping the heat in. All buildings naturally leak air through air vents, extractor fans and natural openings that exist from the original build. Heat loss due to air changes is also calculated and forms an essential part of a heat loss calculation.

By calculating heat loss on a room-by-room bases we obtain all the information needed to design an efficient heating system. We now know what size boiler or heat pump is needed to ensure your heating system has the energy its needs to heat your home at the design outdoor temperature. Did you know the average UK home has a heat loss of less than 7kW?

  • Free advice
  • Fixed price installation
  • Choice of boiler manufacturers
  • Up to 12 Year Warranty
  • Quality workmanship

As well as sizing your boiler, heat loss calculations are used to correctly specify the number and size of radiators needed, or the spacing of underfloor heating pipe and flow rates needed to heat your home to the desired temperature as efficiently as possible.

When purchasing a radiator, it’s important to ensure it will have the correct output to heat your room efficiently. The manufacturer’s quoted output is based on certain parameters being met. A radiator with an output of 1039 watts will only do so if central heating water from your boiler enters at 80°C and leaves at 60°C, with a flow rate of only 0.72 Litres per minute. These temperatures are too high for heat pumps to achieve and although boilers can run at 80°C its very inefficient to do so. Gas condensing boilers will only condense and meet their advertised efficiency when operating with a 50°C flow temperature and 30°C return temperature.

The outcome of a professional heat loss calculation and heating specification will provide a correctly sized boiler or heat pump, correctly sized radiators or underfloor heating, running at the lowest possible flow temperatures, with correctly sized pipework and the correct flow rates, and best of all, a warm and efficient home.

Contact us to arrange a heat loss calculation for your property

Heat Pump Ready Heating Systems

If you aren’t quite ready for a heat pump why not ensure your new heating system is heat pump ready. Not only will this mean minimal disruption during a heat pump installation, but it will also ensure your boiler is efficient. Condensing boilers should operate at a maximum flow temperature of 50°C and a return temperature of 30°C for condensing to fully take place, which is what gives them their efficiency.


  • • Heat loss calculations to EN12831
  • • Domestic central heating design
  • • Heat pump system design
  • • Low temperature heating systems
  • • Heat pump ready central heating systems
  • • LPG, Oil and Natural Gas installations
  • • Solar thermal heating and hot water
  • • Underfloor heating design

Get started on your journey to an efficient heating system today. Contact us

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