Thermal Insulation and Energy in the HomeAQA GCSE Physics: Revision notes

A material with a higher thermal conductivity transfers energy by conduction at a higher rate. For a building, the rate at which it loses thermal energy (cools down) depends on:

• The thickness of its walls - thicker walls lose heat more slowly
• The thermal conductivity of the wall material - lower conductivity materials (like insulation foam) lose heat more slowly than higher conductivity materials (like a single brick or glass)

Unwanted energy transfers - like heat escaping a warm house into a cold outside - can be reduced using thermal insulation, such as loft insulation, cavity wall insulation, and double glazing. In moving parts of a system (e.g. a boiler pump), lubrication reduces friction and wasted thermal energy. Reducing these unwanted transfers means less energy needs to be supplied to keep a home at a comfortable temperature, saving money and reducing environmental impact.

The energy needed to change the temperature of something (like the air or water in a home) is calculated using ΔE = mcΔθ, where c is the specific heat capacity - the energy required to raise the temperature of 1 kg of a substance by 1°C. Materials with a high specific heat capacity (like water) need more energy to heat up, which is why water-filled radiators are effective at storing and releasing thermal energy slowly.

A heating system's efficiency is the proportion of the total input energy (e.g. gas or electricity) that ends up as useful thermal energy in the home, rather than being wasted (e.g. escaping through walls, wasted in the flue): efficiency = useful output energy transfer ÷ total input energy transfer. Improving insulation and using efficient boilers both increase how much of the supplied energy usefully heats the home.