1.7 Choice of installation

You are now in a position to compare the running costs of different methods of heating a house. But another important factor is the cost of installation. This will depend upon the size of the house of course, but it will also depend upon factors like the age and method of construction of the house, and also upon the degree of automation of temperature control that is required. Another point is that it should be sufficient to cope with the extremes of low temperature that could be reasonably expected. Roughly, installation costs increase in the following order:

a) electric fires;

b) electric storage heaters;

c) under-floor electric heating;

d) solid fuel central heating;

e) gas central heating;

f) oil central heating.

Exercise E

1. A roll of 0-025 m fibreglass insulation for the roof costs Ј1 and is 0-5 m wide and 13 m long. How many complete rolls would you need to cover a roof area of 50 m²? How much would this cost? If doing this lowers the U value from 8-4 to 3-0 and you assume an average temperature difference of 7 degC, how many MJ will you save in a heating season? Using coal at Ј15 a tonne with house efficiency of 50% what is your financial saving per season?

2. By what percentage will your heating costs rise if you decide to keep the temperature of your home 2 degC above the standard 7 degC above the outside temperature?

3. How many MJ do you save per heating season in a house of cubic capacity 250 m³ if by weather-stripping the doors you save \ an air change per hour ? Assume a mean tempera­ture difference of 7 degC. How much would this save in one heating season if you were heating by gas costing 8 p/100 MJ with a house efficiency of 70 %?

4. The Gas Board offers 2 alternative ways of payment, A and B units in MJ;

First 25 Next 75 Next 200 Next 700 Next 1000

A 17P 14P up 10p 9p

B Fixed charge of Ј2-75 per quarter and 9 p/100 MJ.

After how many MJ does B become more worthwhile than A? Solve algebraically or graphically.

5. Double glazing improves the U value of windows from 20 to 10. What is the saving in MJ/m² of window area per heating season, if double glazing is put into a living room where the mean temperature difference is maintained at 11 degC? If the heat is supplied by coal at Ј15 a tonne with house efficiency of 40 %, what is the cash saving per square metre per year?

6. The following table gives some comparable ideas of initial costs and running costs for different forms of heating. Assume heat requirements are 100000 MJ per heating season and write down for each item the total cost in pounds after n years. Hence find after how long it would have been cheaper to have installed:

a) item F rather than item A;

b) item D rather than item B;

c) item E rather than item C;

d) item F rather than item G;

e) item H rather than item A.

Item	Heating source	Initial cost	Fuel cost	House efficiency (%)
A	6 electric convector heaters	Ј70	22 p/100 MJ	100
B	6 electric heat storage units	Ј200	9 p/100 MJ	100
C	Under-floor heating	Ј400	9 p/100 MJ	85
D	Gas central heating	Ј450	8 p/100 MJ	70
E	Oil central heating	Ј550	1-8 p/1	70
F	Coke central heating	Ј450	Јi4-5o/tonne	70
G	Present old-fashioned grate burning coal	0	Јi5-50/tonne	40
H	6 Paraffin convector heaters	Ј90	3 P/1	93

In item H, assume the same heat output as oil.

(Note that 1 litre of paraffin produces 1 litre of water during burning!)