Heat loss

Heat loss is a measure of the heat transfer through a building’s fabric from the inside to the outside, generally from the hotter system to the cooler system. This can be due to either convection, conduction, radiation, or a combination. The colder the outside temperature, the greater the heat loss will be through the building fabric.

Heat loss is typically measured in either kilowatts (kW) or British Thermal Units (BTUs), and represents the required energy to maintain a room at a given temperature.

U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are used to measure how effective elements of a building's fabric are as insulators. That is, how effective they are at preventing heat loss. The lower the U-value of an element of a building's fabric, the more slowly heat is able to transmit through it, and so the better it performs as an insulator. Very broadly, the better (i.e. lower) the U-value of a building's fabric, the less energy is required to maintain comfortable conditions inside the building.

Typically, the older a building is, the more it will be susceptible to heat loss unless it undergoes sufficient renovation works to improve airtightness and energy efficiency. Levels of heat loss will vary depending on the type of building; for example, a terraced house will lose a higher proportion of heat through the floor and wall rather than walls, nearly all the heat loss from a flat will be through the outside walls. The following estimate measures indicate the proportionate heat loss from a badly insulated house:

• Up to 25% through the roof.
• Up to 35% through outside walls.
• Up to 25% through doors and windows.
• Up to 15% through ground floors.

(Ref. www.ired.co.uk)

Some of the techniques that can be used to combat and tackle heat loss include:

• Draught-proofing.
• Roof insulation.
• Double-glazing.
• Floor insulation.
• Solid wall insulation.

[edit] Related articles on Designing Buildings Wiki

• Emissivity.
• Heat transfer.
• Mean radiant temperature.
• Passive building design.
• Thermal insulation for buildings.
• Thermal mass.
• Thermal resistance.
• U value.
• Vapour barrier.