Heating Water

Estimating Hot Water Needed

Normally, one of the biggest categories of electricity consumption in a home is heating water.  In order to estimate the energy consumed heating water, one first has to estimate the amount of hot water heated per day.  The form below helps you do that based on the following assumptions:

• Baths and showers are mixed to a final temperature of 40C (which is normal).
• Baths are filled to about 50% full.
• Showers are for 5 minutes each.

To get a total estimate of hot water consumed per day, add the estimated figures above for hot water used for baths and showers  together, and perhaps add a few more liters for dish washing etc.

Estimating Energy Needed to Heat Hot Water

Once you have that, you can then estimate the energy used to heat that hot water.

The form below helps you estimate the energy used by a single conventional electric geyser to heat a given amount of hot water, based on the following assumptions:

• The water is heated to 40C above the cold water temperature (eg. 20C water is heated to 60C).
• A conventional SABS approved geyser is used.

The relevance of the above estimate of electrical energy (kWh) used to heat water using a conventional geyser is the following:

• If you plan to heat water by any alternative form of energy such as using a solar water heater without any form of electrical back up, or gas, then that amount of energy can be subtracted from your existing daily electrical energy requirements.
• If you are looking for ways to make your home more efficient from an electrical consumption point of view, then that estimated amount of energy to heat water can be reduced by approximately 40-50% if you use a solar water heating system that includes electrical back-up heating, or alternatively if you use a heat pump it can be reduced by 60-70%.

 Please note that these calculations are offered as a rough guide based on various assumptions which may not be applicable in your case.  You should do your own calculations to be sure.