Curbing Your Consumption:
Will you be in hot water as the rates rise?
By John Ford
On the 1st of April 2005 your electricity cost rose to an overall rate
of 9.563¢ per kWh for consumption under 750 kWh per month, and
10.45¢ above. Although from November to April the stepped rate
will now apply on a higher threshold of 1000 kWh to allow for heating
The first big change you can make is to lower your hot water tank
temperature. Hotter water loses more energy to the surrounding
environment proportional to the difference in temperature. Lowering it
from 71°C (160°F) to 54°C (130°F) will reduce losses by over 15%. It
will also lessen the dangers of scalding. Don't lower it too much as
it will allow some nasties to grow in the tank. Insulating electric
tanks, and adding insulation to pipes will also reduce losses.
How much does your domestic hot water actually cost? How much can you
save by making some changes? A home using 500 litres of electrically
heated hot water a day (at 54°C) uses 17 kWh and costs $1.67 ($51 per
month, $610 per year). A gas heated tank producing 500 litres uses
about 2 m3 and costs* 92¢ ($28 per month, $336 per year).
*Assuming gas price (non-contract) is about 46¢ overall per m3.
A 10 minute shower with a low-flow head (you have converted your
shower heads to low-flow?) uses about 50 litres of hot water. That's
16.7¢ of electricity or about 7.8¢ of gas. Cutting shower
times in half for a family of three would save $90 a year
(electricity) or $42 (gas). Drawing a bath uses lots more hot water
than a shower. (about 100 litres.)
A top-loading clothes washer can use about 70 litres of hot water on
the 'hot' setting and 35 litres of hot water on 'warm'. Switching from
hot to cold would save 23¢ of electricity (or 11¢ of gas)
per load. If you do four loads a week, that's about $50 (or $23) a
year. Front loaders use about 50% less water than top loaders for more
Dishwashers use hot water and can use an internal heating element so
that it runs at 60°C. Some dishwashers lack the element and require
that you set your hot water tank to 60°C. It might be time to replace
if this is the case. Of course hand washing is even 'greener!'
The first observation from the above cost estimates is that gas can be
about half the cost of electricity with current prices. Gas hot water
tanks cost more to buy, and more to install. If you already have a gas
furnace, switching your water heater to gas may make economic
sense. As mentioned in a previous column, gas water heaters will run
during a black-out, which might also appeal.
Ask the Miser
If you would like to see answers here to your questions about energy
consumption, email them to
John Ford is a technology consultant, and owner of a small energy