How is heat transferred from a house, and how can we reduce these energy losses?
Heat transfer by conduction, convection and radiation, and methods of reducing energy loss from a house such as insulation.
A focused answer to the WJEC GCSE Science Double Award Unit 3 topic on reducing energy loss, covering heat transfer by conduction, convection and radiation, and the methods used to reduce energy loss from a house such as loft insulation and double glazing.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
WJEC Double Award Unit 3 wants you to describe heat transfer by conduction, convection and radiation, and explain how energy loss from a house can be reduced.
The three types of heat transfer
Metals are good conductors; air, water and most non-metals are poor conductors (good insulators). Convection happens only in fluids; radiation happens from any warm object.
Conduction
In conduction, particles in the hot part of a solid vibrate more and pass energy to neighbouring particles. Metals conduct well because they have free electrons that carry energy quickly. Trapped air is a poor conductor, which is why insulating materials rely on trapping pockets of air.
Convection
Convection currents explain how a radiator heats a whole room and why warm air collects near the ceiling.
Radiation
All warm objects emit infrared radiation, and hotter objects emit more. Dark, matt surfaces are good emitters and absorbers of radiation, while light, shiny surfaces are poor emitters and good reflectors. This is why shiny foil behind a radiator reflects heat back into the room.
Reducing energy loss from a house
Methods of reducing heat loss usually work by trapping air (a poor conductor) or reflecting radiation:
- Loft insulation: traps air in the roof space, reducing conduction through the roof.
- Cavity wall insulation: fills the gap in the walls with a material that traps air, reducing conduction.
- Double glazing: a layer of air (or vacuum) between two panes reduces conduction through windows.
- Draught excluders and carpets: reduce heat loss through gaps and the floor.
These reduce the energy needed to heat the house, saving money and reducing the fuel burned.
Payback time
When choosing insulation, people compare the cost of fitting it against the money saved each year on heating. The payback time is how long it takes for the savings to equal the cost: payback time = cost of installation / annual saving. For example, loft insulation costing 300 pounds that saves 100 pounds a year has a payback time of 3 years. After that, it saves money every year. Cheaper measures (such as draught excluders) often have a short payback time, while expensive ones (such as double glazing) take longer to pay back. Calculating payback time is a common maths question in this topic.
Comparing the methods
Different methods reduce different losses, and exam questions often ask you to compare them. Loft insulation and cavity wall insulation mainly cut conduction through the roof and walls. Double glazing cuts conduction (and some convection) through windows. Draught excluders reduce convection as warm air escapes through gaps, and shiny foil behind radiators reflects radiation back into the room. The best choice depends on where the house loses most heat and on the cost and payback time, so a good answer names the method, the type of transfer it reduces, and weighs cost against saving.
Try this
Q1. Which type of heat transfer can travel through a vacuum? [1 mark]
- Cue. Radiation (infrared).
Q2. Why is trapped air used in insulation? [1 mark]
- Cue. Air is a poor conductor of heat, so it reduces heat loss by conduction.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain how loft insulation and double glazing each reduce the energy lost from a house.Show worked answer →
A Unit 3 explain question worth 4 marks. Reward: loft insulation (such as fibreglass) traps air, which is a poor conductor, reducing heat loss by conduction through the roof (2); double glazing has a layer of air (or vacuum) between two panes of glass, which is a poor conductor, reducing heat loss by conduction through the windows (2). Markers credit trapping air/poor conductor and the reduction in conduction for each. A common error is to say insulation "keeps the heat in" without explaining the poor conduction.
WJEC style3 marksDescribe how heat is transferred by convection in a room heated by a radiator.Show worked answer →
A Unit 3 describe question. Reward: the radiator heats the air near it, which expands and becomes less dense, so it rises (1); cooler, denser air sinks to take its place and is heated in turn (1); this sets up a convection current that circulates warm air around the room (1). Markers credit the warm air rising because it is less dense, the cool air sinking, and the convection current. A common error is to say heat "rises" rather than the warm air.
Related dot points
- Energy stores and transfers, the conservation of energy, wasted energy, and calculating efficiency.
A focused answer to the WJEC GCSE Science Double Award Unit 3 topic on energy, covering energy stores and transfers, the conservation of energy, energy wasted as heat, and calculating efficiency with the efficiency equation.
- Renewable and non-renewable energy resources, how power stations generate electricity, and the advantages and disadvantages of different resources.
A focused answer to the WJEC GCSE Science Double Award Unit 3 topic on energy resources, covering renewable and non-renewable resources, how power stations generate electricity, and the advantages and disadvantages of each resource.
- The particle model of solids, liquids and gases, density, and changes of state as physical changes.
A focused answer to the WJEC GCSE Science Double Award Unit 6 topic on the particle model, covering the arrangement of particles in solids, liquids and gases, density, and changes of state as physical changes.
- Specific heat capacity and the equation for energy, internal energy, and the energy needed for a change of state.
A focused answer to the WJEC GCSE Science Double Award Unit 6 topic on heating, covering specific heat capacity and its equation, internal energy, and the energy needed during a change of state when the temperature stays constant.