Hot water costs

voyagerbear

I am having a 'dispute' with my son regarding the cost of heating water. I believe it is cheaper to have the water heating on a timer morning and evening as no one is home during the day. But my son insists that it costs no more having it on constant as it remains hot and the gas boiler only fires up when the thermostat kicks in.

Please advise who is right here....... am I wrong?

thanks

macman

Constant is more expensive, as it's then losing heat as soon as it comes up to temp-if no -one's using it there is no point in heating it in advance.
Even if your hot water tank is well lagged it still loses some heat all the time.
This question is usually asked at least once a week in relation to leaving the CH on all day, and the answer is always the same.

st999

the answer is always the same

No it's not, It depends!

I went on holiday so turned my gas off. when I came back the hot water in the hot water tank was cold, what do you expect after 14 days?

I normally use 17 kWh of gas a day, to heat water and the pilot light, the pilot light uses 3 kWh. So actually 14 kWh to heat the water.

So I turned the gas back on at the meter and took a reading, it was the same reading when I turned the gas off 14 days previously.

Next day, 24 hours later, I read my meter and calculated my usage and I had used 34 kWh of gas, so I calculate that I used 17 kWh of gas to heat the tank up.

So if I was to turn my pilot light off, use all the hot water in the tank in a day then turn the pilot light on 24 hours later I would use an extra 17 kWh of gas a day to heat the cold water up again than what I am using by leaving it on all the time.

So as I said at the start, IT DEPENDS!

I should add that my hot water tank has foam insulation then an extra lagging jacket and when I added that my wife complained that the towels were no longer hot in the cupboard.

So me it costs less to leave it on all the time

voyagerbear

Thanks for your replies, although, I'm not talking about turning it off for any great length of time, it would come on for a couple of hours a.m. morning showers and then p.m for the evening and off again overnight. Say 2 hours a.m. 2 hours p.m. So it shouldn't get cold.

KG-THPP

Depends on how well your house is insulated. In poorly insulated houses cranking on the heating only when 100% needed is cheaper. In a well insulated house that has minimal heat losses then trickle heating is better.

macman

voyagerbear wrote: »

Thanks for your replies, although, I'm not talking about turning it off for any great length of time, it would come on for a couple of hours a.m. morning showers and then p.m for the evening and off again overnight. Say 2 hours a.m. 2 hours p.m. So it shouldn't get cold.

It doesn't matter how long it's on or off for. The amount of energy needed to raise the temp of x litres of water by y degrees is a constant, everything else being equal. As long as the system is on and the stat is calling for heat, it will burn gas and cost money. If heat is then lost before actual usage (as it will be) then part of that cost is wasted.
On the basis of what st999 said, it would make sense to keep your kettle near to boiling all day to make a cup of tea some time in the future.

st999

it would make sense to keep your kettle near to boiling all day

Why? This keeps being brought up.

It is not a fair comparison as the kettle is not insulated.

How much heat would a kettle lose if it was insulated to the same level as a hot water tank and if there was no spout for heat to escape from?

Exactly the same as a hot water tank as then that is what the kettle becomes.

Anyway it works for me so there!

I am just waiting for the gas monitor equivalent of the electricity monitor to become available and then gas usage can then be monitored every 6 seconds like electricity is at present monitored.

st999

The best solution for the OP is to do what is often suggested. Read the meter, leave the water on all the time for a couple of days, read the meter again, then put the water on timed for a couple of days and read the meter again.

Then compare the results.

At least with hot water the weather and temperature should not make a significant difference.

voyagerbear

I think if i can get passed the 'dispute' stage, he should do some monitoring regarding the usage and see for himself if it makes any difference. I don't suppose anything I have to say will matter!!!!

Thanks everyone....appreciated.

macman

It is not a fair comparison as the kettle is not insulated.

That's why I said 'everything else being equal'...
You don't need a physics degree to work out that leaving it on when it's not needed must cost more, unless you can prevent any heat loss whatsoever.

st999

That's why I said 'everything else being equal

that is what is said all the time but it is not equal so why is it often stated as fact?

I will give you a fact

It costs me less money in gas to leave my hot water on all the time than if I turn off the pilot light, use all the hot water in the tank, then turn on the pilot light to heat a tank full of cold water back up to 60 deg C.

that is why I said IT DEPENDS.

Not all circumstances are identical.
Another fact, not relevant to this discussion, although another poster mentioned heating, If I leave my central heating on 24 hours a day it uses more gas than just having it on 12 hours a day.