Heating Hot water all the time or when needed

[Janice]

I have warm air heating and a Janus gas water heater which heats the water for a hot water tank in a cupboard. The ONLY way to control the heater is a black thermostat knob behind a panel in the heater. Therefore it is left on all the time. This uses about 33Kwh of gas a day for one bath and two 5 minute power showers. Plus dishwashing etc.

There is NO immersion heater or thermostat on the hot water tank or a timer. It even works if the electricity is turned off. (the heating doesn't though) So how much would it cost if I was to turn off the gas every day and heat up a tank of water from cold or will it cost about the same?

It presently costs me £1.10 to keep the water hot all the time.

Thank you, Jan

[Doctor Drivel]

The Janus has an integral thermostat that control she cylinder temperature. You are right it is a non-electric unit. The later models had electric control. It may be possible to have it converted and a switch then turns it off-on or a timer added switches it on-off.

[meow2222]

33kWh seems very high. 3kWh is more than enough for a bath plus dishwashing.

NT

[TheScullster]

"Janice" wrote

The cost will be dependent on the efficiency of the heat source (and any associated controls) and the level of insulation around the hot water store tank/interconnecting piping. Sounds like the best thing you could do initially is to ensure that insulation is good. If it isn't, then record your gas usage now and then lag the tank/piping to compare before and after costs.

As others have said, the next step is introducing control. But if your insulation efficiency is high, then the argument for intermittent heating vs constant becomes less of an issue.

Phil

[Janice]

Hi I did a reading on my meter for a second day and discovered that I did not use 33Kwh for one days hot water. I had rounded up the reading as it was less that 1 unit. Today it was less than 1 unit used so I looked for a gas bill from last year when the heating was not on and I am using on average

16Kwh so at 3.6p per Kwh it is costing me about 60p per day to heat the hot water.

Is that a more reasonable cost? What do other people pay per day to heat their water?

The hot water tank has foam insulation plus an extra jacket and most of the hot water pipes are lagged with foam.

Jan

[Harry Bloomfield]

Janice explained on 21/04/2009 :

I would suggest that is quite reasonable for constantly hot water.

[auctions]

You can do a basic calculation of the wasted energy quite easily. litres of water x degrees celsius heated x 1000 =3D calories needed to heat. Convert to kWh using an online calculator.

Example: bath @100l +2 x showers @50l + washing. Say 250 litres per day. Average temperature of the water used, say 45 degrees, so about

40 degrees increase. 250 x 40 x 1000 =3D 1000000. Converts to 11.63kWh.

Obviously you can get a better estimate if you know how big your bath is and the flow rates of your shower, but based on this, you're getting about 12kWh of useful heat output for 16kWh of heat input, which is quite reasonable. By not having the heating on constantly, you'll save part of the wasted energy, but nowhere near all of it.

A

[Doctor Drivel]

You can't do better unless you change the control system on the Janus.