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How is thermal energy transferred, and how can heat loss from a home be reduced?

Conduction, convection and radiation, the factors affecting heat loss, methods of insulating a house, and judging cost-effectiveness using payback time.

A focused answer to WJEC GCSE Physics topic 1.3 on making use of energy, covering conduction, convection and radiation, the factors affecting heat loss from a house, insulation methods, and how to compare them using cost-effectiveness and payback time.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this topic is asking
  2. The three ways heat is transferred
  3. Heat loss from a house
  4. Insulation methods
  5. Cost-effectiveness and payback time
  6. Try this

What this topic is asking

WJEC wants you to describe conduction, convection and radiation, explain the factors that affect heat loss from a house, describe insulation methods, and judge their cost-effectiveness. This is part of topic 1.3 Making use of energy in Unit 1 of WJEC GCSE Physics (3420).

The three ways heat is transferred

Heat loss from a house

A house loses thermal energy through the roof, walls, windows, floor and through gaps where air leaks (draughts). The rate of loss is larger when the temperature difference between inside and outside is greater, when the materials are good conductors, and when there are large areas or gaps for convection. Reducing any of these slows the loss.

A warm house cools fastest when it is much hotter than outside, because the rate of heat transfer grows as the temperature difference grows. This is why a house loses heat most quickly on a cold winter night and why turning the thermostat down a little can save a surprising amount of energy. Warm air rising through the roof makes the loft a major route for losses through convection, so loft insulation is often the most cost-effective first step. Single-glazed windows lose heat readily because glass conducts and because a single pane has nothing to slow convection on either side, whereas double glazing traps a still layer of air or argon between two panes to slow both conduction and convection.

Insulation methods

Cost-effectiveness and payback time

Try this

Q1. State which method of heat transfer can occur through a vacuum. [1 mark]

  • Cue. Radiation (infrared waves need no medium).

Q2. A measure costs £600\pounds 600 and saves £150\pounds 150 per year. Find its payback time. [2 marks]

  • Cue. 600150=4 years\dfrac{600}{150} = 4\,\text{years}.

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 20183 marksExplain how loft insulation and cavity wall insulation reduce heat loss from a house.
Show worked answer →

A topic 1.3 Explain question. Both insulators trap air, and trapped air is a poor conductor of heat (1 mark). Loft insulation reduces the heat conducted and convected through the roof, where warm air rises and would otherwise escape (1 mark). Cavity wall insulation fills the gap between the walls with trapped air or foam, reducing conduction and convection through the walls (1 mark). Markers reward the trapped air, the poor conduction, and reducing both conduction and convection. A common error is to ignore convection or to say insulation adds heat.

WJEC 20214 marksA homeowner can fit loft insulation costing £300\pounds 300 that saves £60\pounds 60 per year, or draught-proofing costing £40\pounds 40 that saves £20\pounds 20 per year. Calculate the payback time of each and state which is more cost-effective at first.
Show worked answer →

A topic 1.3 cost-effectiveness question. Payback time is cost divided by annual saving. Loft insulation: 30060=5 years\dfrac{300}{60} = 5\,\text{years} (1 mark). Draught-proofing: 4020=2 years\dfrac{40}{20} = 2\,\text{years} (1 mark). Draught-proofing has the shorter payback time, so it is more cost-effective at first because it pays for itself sooner (1 mark). Over many years the loft insulation may save more in total because of its larger annual saving (1 mark). Markers reward both payback times, the shorter one being more cost-effective initially, and the long-term point.

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