Geyser Calculations: Get Your Water Heater Geyser Price

Categories: Advice, Guides, Solar Geysers

If there is one thing everyone would like to do, it’s getting the electricity bill down. We substitute things like the electric kettle for the gas option, only to find it’s hardly made a dent. That’s because the biggest waste of energy can be found in the geyser. Out of all the appliances that run aimlessly, the geyser is the biggest culprit in terms of running up the monthly costs. In this article we’ll look at how you can calculate the costs, and whether your geyser is truly the biggest electrical expenditure you have. Hopefully you’ll be able to clearly compare a water heater geyser price with a long term plan.

Calculating Water Usage

The geyser is only really a waste when you’re not using any hot water, so it’s important to make that distinction. The first step in getting an accurate number for the energy the geyser uses. We need to figure out how much hot water you are using per day. In order to get your specific water heater geyser price point, you’ll have to make notes over the course of a month. This means paying meticulous attention every time hot water is used. There are programs that help with this sort of thing, but to better understand the calculations part, we’re going to use an average of 110L per day. This is the typical amount for two people at 55L per person..

Now you have to find the temperature of your geyser, which can be adjusted accordingly, but for argument’s sake we’ll assume it’s 70 degrees. So we’ve got:

  • 110L that heats up to 70 degrees on a daily basis

Cold water has an average heat of 15 degrees, and so there is a 55 degree difference when the water is heated.

  • 70 – 15 = 55

Now we have to make the conversion from weight and degrees into energy. This is done by adding the specific heat capacity of water, which is 4.2. The calculation now looks something like this:

  • 110 x 55 x 4.2 = 20 790 kilo-joules of energy

But given that your electric bill is going to show kilo-watt hours, another calculation needs to be made. The 20 790kj of energy needs to be divided between 3 600, which is the amount of seconds in a day.

  • 20 790 / 3 600 = 5.775 kilo-watt hours

Now we can deduce that 5.775 of kilo-watt hours are actually being used on a daily basis. Unfortunately the geyser is going to heat up the water, regardless of whether the hot water is being used. When the thermostat switches off the geyser the water is gradually going to get colder, until it reaches a specific point where the thermostat kick-starts the geyser again. How quickly the heat is lost depends on the insulation of the tank.

What does it All Cost?

Your geyser should have a sticker on it that tells you the size and the efficiency level. Let’s use another example here and say you have a 150L tank with an efficiency level of D. According to the sticker the Standing Loss of energy in kWh per day is 2.1. This means you are using a total of 7.875kWh per day.

  • 5.775 + 2.1 = 7.875kWh

The last part of the calculation involves the price per unit, which ranges at R1.40. After getting a monthly total of kWh, you multiply the two.

  • 7.875 x 30 = 236.25kWh
  • 236.25 x 1.4 = R330.75

On hot water alone you are spending R330.75, while R88.20 of the amount is literally for nothing, because it falls under the Standing Loss. Now add everything else that comes with your municipality bill and you’ll start to see the difference between a solar water heater geyser price, and a conventional one. Also take note that these calculations are based on a new geyser that works exactly the way it should. Over time geysers lose a lot of efficiency.


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