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.

3 thoughts on “Heating Water

  1. Do you sell solar panels for geysers? We want to install a solar panel for my mother, her geyser is 150L and it’s only her staying there.

  2. Hi I found your information regarding hot water extremely beneficial.
    I want to “stretch your gray matter”😁..a bit if you dont mind?
    I was informed by a person who sells solar equipment that in my case with a 150litre kwokot hot water geyser..I can use 4 solar panels and connect the solar terminal wires to a box unit .There asre also connecters in this box for the thermostat and element wires of the geyser as well as connections for poer supply from eskom from db board in house.
    Also there is a small box switch desperately that I can switch between solar power or Eskom power.
    So no inverter or battery needed…just plain solar panels and this “box”
    The way I see it the element is for a.c. and solar power is dc?
    Is that possible

    Will appreciate your input and technical response to my issue
    Regards AdolfB

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