1st Nov '25

Home Efficiency

To maintain our homes at a higher temperature than the surroundings we have to supply as much heat energy as is being lost. To save energy, and therefore money, we should the losses. We do this by reducing the rate of energy transfer.

We will look at ways to reduce conduction through the walls.

We can reduce conduction by putting a poor conductor between the hot room and the cold outdoors. One of the best insulators is air. A cavity wall has a layer of air between two walls. While it does reduce conduction, a will be set up in the air gap.

To stop the convection current we can trap the air in small pockets or bubbles using wool or foam.

Up to 20% of heat energy can be lost through our lofts. They are designed to allow air movement beneath the roof to stop the timber rotting. To reduce this we can install fibre glass insulation between the rafters of the ceiling below. This again traps air in pockets and works in the same way as cavity wall insulation.

Draughts are large movements of cold air from outside. This is therefore a type of . We can reduce them by having well fitted doors and windows, or adding seals and brushes to poorly fitting ones. will also reduce the movement of cold air by windows.

Double Glazing reduces the conduction of heat through the window by having an air gap too narrow for convection to start.

Payback Period

A simple method of comparing the relative cost savings is the 'payback period' method. This is calculated by dividing the installation cost by the annual saving. This will tell you the number of years that it takes for the savings to pay for the installation.

Method Installation cost Annual Saving Payback Period

Loft
Insulation £400 £80 5 years

Cavity Wall
Insulation £600 £30 years

Double
Glazing £1800 £ 30 years

Draught
Excluders £ £20 2 years

Method	Installation cost	Annual Saving	Payback Period
Loft Insulation	£400	£80	5 years
Cavity Wall Insulation	£600	£30	years
Double Glazing	£1800	£	30 years
Draught Excluders	£	£20	2 years

We should do the method with the shortest payback period first, so that we will start saving money as soon as possible.

What method of 'insulation' should we do first, what should be done last and WHY?

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