How long to heat 30 gallon water tank

someanonbloke

Hi, I have a 30 gallon water tank, which is heated by a 3KW electric heater.

The plug is on a 24hr mechanical meter and I'm trying to set the times for the heater to switch on.

Currently, I have it set to be on 2 hrs early morning for when people have showers (after 3 showers there's not much hot water left) and 2 hrs in the early evening.

Am I right in thinking that it takes about 2 hrs to heat the tank up?

Is 2 hrs morn/eve enough? Cheers.

Avoriaz

Specific Heat of Water = 4.1813 kJ/l/C

30 gallons = 136 litres

If starting temperature is say 20°C (ambient house temp) and you want to heat it to 60°C = 40°C rise in temp.

136 Litres x 4.1813 x 40 = 22746.272 kJ

22746.272 kJ / 3kW = 7,582 Seconds = 126 minutes = 2 hours 6 minutes.

That does not allow for heat losses but it does look as if your two hours is about right.

If the tank is poorly insulated or is in a loft or other unheated room you will need to increase the heating time in colder weather.

Trial and error should get it right eventually.

Adjust my calculation for other temperatures. For example you might only need water at 55°C.

Edit: At times, especially in winter, the incoming water will be very cold so the water in the tank may be well under 20C. Again that means longer heating times to bring it up to 55C or 60C.