Reducing Heat loss
Heat Loss from houses
Look at the five ways heat energy is lost from a
house.
Each area loses different amounts of energy.
1. In which area is the most heat energy
lost? ____________________________
2. In which area is the least heat energy
lost? ____________________________
3. Different houses could have different
answers – why?
_________________________________
_________________________________
This house loses the most heat energy from the walls and the least from the floor.
Use the numbers below to fill in the table to show the amount of heat lost per second
from each area.
180J/s
360J/s
How much
energy is lost
Area
Highest
Walls
2nd highest
Roof
240J/s
Amount of
heat lost (J/s)
% of total
heat losses
120J/s
300J/s
Insulating materials
Windows
2nd lowest
Draughts/Door
Lowest
Floor
Calculating the percentage of heat lost through the Roof
%
= number x 100
total



First you need to work out the total energy loss from the house.
Total energy loss = ______________ J
The roof loses _________ J out of ___________ J

Write this as a decimal and multiply by 100 = ___________ x 100% = ________ %
 Calculate the percentage heat loss from each area and fill in the % column in the
table.
Reducing Heat Loss
 In pairs, think about different materials people can use to reduce heat loss and fill
in the final column.
By reducing heat losses, people can reduce how much energy they use. This means
saving money on their energy bills.
Practice exam question 1
•
Energy consultants tell their customers how to
save money. They explain how people can
reduce energy loss from their homes.
•
This picture shows the percentage energy loss
from different parts of a house.
(b) Calculate the percentage energy loss through the
walls of the house.
......................................................................................................................
(c) Suggest the two most effective methods of reducing heat loss for this house.
1 ...................................................................................................................
2 ...................................................................................................................
Reducing energy consumption
By reducing heat losses, people can reduce how much energy they use. This means
saving money on their energy bills.
Some ways of reducing heat loss are very expensive.
People need to think about 3 things before they spend money on insulating these areas.
1. Installation Cost
2. Savings from energy losses
3. How long will you live in the house.
Payback time
This is the time in years to get back the money you have spent on insulation from the
savings you have made.
Payback time = Cost of installing
Savings
 Calculate the payback time for each method and fill in the table below.
 Hint - the savings are made from the energy losses
Where is
heat lost?
Cost of
energy losses
(£)
Method
Installation
cost (£)
roof
250
Fibre glass insulation
300
walls
350
Foam filled cavity wall insulation
1050
windows
300
Double glazing
4500
Payback time
(years)
doors
80
Draught proofing
40
Cost effectiveness
This compares the TOTAL SAVINGS made over a few years compared to the cost of the
insulation.
 Using the information in the table, work out the profit made after 5 years for:
1. Draught proofing
How much is saved in 1 year? = _____ How much is saved in 5 years? = _____
What profit is left over? =
2. Roof insulation.
How much is saved in 1 year? = _____ How much is saved in 5 years? = _____
What profit is left over? =
Hint – don’t forget to take away the cost of the installation
Answers
Savings from draught proofing = __________
Savings from Fibre glass insulation = ________
So which method of insulation is the most cost effective over 5 years?
______________________________________________________________________
So, when answering questions, you need to look at:


whether or not you will get back your money (payback time) AND
if you do get your money back, how do the total savings over time compare
to the cost (profit)
PAYBACK TIME &
PROFIT
Practice exam question 2
The table shows the installation costs and yearly savings on energy bills for different
methods of insulating a house.
a) Give one reason why loft insulation is often fitted to an old house before double
glazing or cavity wall insulation.
_______________________________________________________
b) The time it takes for the saving on energy bills to equal the cost of installing the
insulation is called the pay-back time.
Calculate the pay-back time for loft insulation
______________________________________________________________
Pay-back time = ____________________ years
(2 marks)
Practice exam question 3
The table gives information about some ways of reducing the energy consumption in a
house.
Which way of reducing energy consumption is most cost effective over a 10 year period?
To obtain full marks you must support your answer with calculations.
Hint – you need to work out the profit.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_________________________________________________________________ (3 marks)
Practice exam question 4
The diagram below shows a house which
has not been insulated. The cost of the
energy lost from different parts of the
house during one year is shown on the
diagram.
The total cost of the energy lost during
one year is £1000.
a) What is the cost of the energy lost
through the floor? (show your working out)
_______________________________________________________ (2 marks)
b) Suggest one way of reducing this loss.
________________________________________________________ (1 mark)
The table below shows how some parts of the house may be insulated to reduce energy
losses. The cost of each method of insulation is also given.
c) Which method of insulation would you install first? Explain why.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_______________________________________________________________
(3 marks)
d) Which method of insulation would you install last? Explain why.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
________________________________________________________________ (3 marks)
Practice exam question 5
The diagram shows how much heat is lost each
second from different parts of an uninsulated house.
Each year the house loses £760 to heat.
a) What percentage of energy is lost through the
roof?
__________________________________
b) How much money is being wasted though the
roof?
________________________________________
c) Insulating the loft would cut the heat lost through the roof by 50%. How much
money would loft insulation save every year?
_________________________________________________________________
d) The loft insulation has payback time of 1.5 years.
How much did the loft insulation cost to buy?
_________________________________________________________________
_________________________________________________________________
Cost of loft insulation = £ ___________
(4 marks)
Answers
Exam question 2
a) most cost effective = 1 mark
accept it is cheaper or lowest cost
accept shortest payback time
accept in terms of reducing heat loss by the largest amount
do not accept it is easier
ignore most heat is lost through the roof
b) 4 years = 1 mark
Exam question 3
hot water boiler = 1 mark
four calculations correctly shown = 2 marks
200 × 10 – 1800 = £200
100 × 10 – 2400 = –£1400
50 × 10 – 600 = –£100
20 × 10 – 75 = 125
accept four final answers only
accept obvious rejection of solar water heater and underfloor heating, with
other two calculations
completed any 1 complete calculation correctly shown = 1 mark
showing each saving × 10 of all four calculations = 1 mark
Exam question 4
a) 1000 – (250 + 350 + 100 + 150) or 1000 – 850 = 1 mark
Answer = £150 = 1 mark
b) (Named) floor covering OR Insulation under floor = 1 mark
c) Draught proof doors or fibre glass in loft or foam filled cavity
There is one mark for the method with 2 marks for the explanation.
draught proofing
1 mark for choosing draught proofing
 Very low cost/easy to install
 Repays for itself quickly/cost recuperated quickly
 Reasonable energy saving
any 2 for 1 mark each
For loft insulation
1 mark for choosing loft insulation
 Second lowest installation cost/easy to install
 Reasonable large energy savings for this cost
 Reasonable payback time
any 2 for 1 mark each
For foam filled cavity
1 mark for choosing loft insulation
 Biggest energy/cash saving
 Cost effective
any 2 for 1 mark each
d) Double glazing gains 1 mark
 Costs most
 Saves least energy
 Least cost effective
any 2 for 1 mark each
Exam question 5
a) 25% = 1 mark
b) £190 = 1 mark
c) £95 = 1 mark
d) £142.50 = 1 mark