How much gas to heat hot water for 1 hour ?

Jimatalveston

Hi all
How much KWh gas do you use to heat your hot water only for 1 hour ?
Using a conventional gas boiler with hot water cylinder.

Just got a smart meter fitted and we’re using betweeen 10-13 KWh

Thank you.

Cardew

Depends on:

1. Capacity of HW tank.

2. Temperature of water in tank before you start boiler.

3. Temperature you want to reach - set by thermostat.

4. Output of boiler in kW during the hour.

I have a large HW tank and a large boiler. If water in tank was cold, in an hour I could use much more than 13kWh.

System

Cardew wrote: »

Depends on:

1. Capacity of HW tank.

2. Temperature of water in tank before you start boiler.

3. Temperature you want to reach - set by thermostat.

4. Output of boiler in kW during the hour.

I have a large HW tank and a large boiler. If water in tank was cold, in an hour I could use much more than 13kWh.

I would agree with all the above but add some further variables:

a. No of people in the home.

b. Bath or shower and frequency.

c. Height of temperature probe in cylinder.

d. HW programmed ON time.

This month, so far, I have used 168.3kWhs of gas for HW heating, cooking and one day of CH, My cylinder is a 250Litre Oso unvented cylinder with a temperature probe about 1/3 up from the cylinder floor. HW is maintained in the temperature range 60 to 55C.

When HW only is being heated, daily usage is in the range 5.6kWhs to 7.9kWhs. The latter is when my wife runs a bath.

Ectophile

My boiler is only on for 40 minutes, as that's enough to heat the tank back up from warm.

I reckon that takes between about 3 and 6kWh. I can't measure it any better than that, as it's one, or sometimes two, units on the lowest digit on the gas meter.

Gloomendoom

Jimatalveston wrote: »

Hi all
How much KWh gas do you use to heat your hot water only for 1 hour ?
Using a conventional gas boiler with hot water cylinder.

Just got a smart meter fitted and we’re using betweeen 10-13 KWh

Unless somebody else has exactly the same installation as you, a comparison is pretty meaningless.

If I ran my boiler for an hour to heat the hot water cylinder it may use the same amount of gas as yours, however, for twenty minutes the gas would be heating the mass of the boiler and the water in it, then the hot water would have to make its way by gravity from the boiler room into the main house and upstairs to the bathroom where the hot water cylinder is. An hour wouldn't be long enough to heat much water in the tank. In fact, unless the central heating is required at the same time, we just use the electric immersion heater. It works out cheaper than running the boiler.

[Deleted User]

Also depends on how well its insulated