Heating hot water tank all day
Discussion
We have a new condensing boiler on a sealed system. Our heating controls are quite basic and only allow heating + hot water on and off on 2 timed cycles per day but not individually (i.e. we can’t have heating times different to hot water times). What we normally do is manually switch off the hot water after it’s been on a while as we need heating to remain on.
I realise that once the hot water tank is to temperature it stops calling for heat anyway, but I wondered whether we should just leave it on all the time and us switching it off is pointless? The tank is in the middle of the house upstairs and lagged with a some sort of solid foam.
I also realise we should get a more sophisticated timer but we’ve just had lots of work done and I’d like a break from tradesman visits!
I suppose what I don’t know is how much heat the tank loses and therefore if we’d be wasting heating the tank say in the evening when the water won’t be used until the next morning?
I realise that once the hot water tank is to temperature it stops calling for heat anyway, but I wondered whether we should just leave it on all the time and us switching it off is pointless? The tank is in the middle of the house upstairs and lagged with a some sort of solid foam.
I also realise we should get a more sophisticated timer but we’ve just had lots of work done and I’d like a break from tradesman visits!
I suppose what I don’t know is how much heat the tank loses and therefore if we’d be wasting heating the tank say in the evening when the water won’t be used until the next morning?
I think you need to do a test.
Have your hot water tank heated up to temp, and not heating. Do a task such as washing your hands with hot water, washing up etc, see how long the tank then starts calling for heat.
I leave mine on continuously - its about 5 minutes for the tank to come on, call for heat and turn off in the scenarios I described above.
Have your hot water tank heated up to temp, and not heating. Do a task such as washing your hands with hot water, washing up etc, see how long the tank then starts calling for heat.
I leave mine on continuously - its about 5 minutes for the tank to come on, call for heat and turn off in the scenarios I described above.
devnull said:
I think you need to do a test.
Have your hot water tank heated up to temp, and not heating. Do a task such as washing your hands with hot water, washing up etc, see how long the tank then starts calling for heat.
I leave mine on continuously - its about 5 minutes for the tank to come on, call for heat and turn off in the scenarios I described above.
That's an option I can try. I've always thought that was less efficient than heating the tank in one go but now wonder if there is any difference.Have your hot water tank heated up to temp, and not heating. Do a task such as washing your hands with hot water, washing up etc, see how long the tank then starts calling for heat.
I leave mine on continuously - its about 5 minutes for the tank to come on, call for heat and turn off in the scenarios I described above.
OK, not exactly your situation due to boiler type but here goes.
When in uni we were doing mathematical modelling. One of the simple models was comparing heating into a storage tank. Based on the copper cylinder type normal in those days.
Basically the key to best economy was good insulation of the tank and leaving the heater switched ON to maintain the water temperature. The initial heating to temperature was the main cost, a thermostat to compensate for small heat loss through insulation was minimal. Of course, this was for a system where water was not being drawn out by taps, showers, dishwashers etc. And little need for reheating. If you are out all day or sleeping at night then that is where the savings were being made.
No insulation meant heat lost was costly. Repeated heating then losing the heat lost whilst switched off was also costly.
Your system might behave in a similar way in principle but as you have a small tank your demand for heat is different.
When in uni we were doing mathematical modelling. One of the simple models was comparing heating into a storage tank. Based on the copper cylinder type normal in those days.
Basically the key to best economy was good insulation of the tank and leaving the heater switched ON to maintain the water temperature. The initial heating to temperature was the main cost, a thermostat to compensate for small heat loss through insulation was minimal. Of course, this was for a system where water was not being drawn out by taps, showers, dishwashers etc. And little need for reheating. If you are out all day or sleeping at night then that is where the savings were being made.
No insulation meant heat lost was costly. Repeated heating then losing the heat lost whilst switched off was also costly.
Your system might behave in a similar way in principle but as you have a small tank your demand for heat is different.
Edited by sospan on Thursday 27th February 18:50
ro250 said:
Alucidnation said:
ro250 said:
Sure, I know we could get a new timer, I'm asking in relation to our current setup.
That’s why I asked what programmer you have gotsospan said:
OK, not exactly your situation due to boiler type but here goes.
When in uni we were doing mathematical modelling. One of the simple models was comparing heating into a storage tank. Based on the copper cylinder type normal in those days.
Basically the key to best economy was good insulation of the tank and leaving the heater switched ON to maintain the water temperature. The initial heating to temperature was the main cost, a thermostat to compensate for small heat loss through insulation was minimal. Of course, this was for a system where water was not being drawn out by taps, showers, dishwashers etc. And little need for reheating. If you are out all day or sleeping at night then that is where the savings were being made.
No insulation meant heat lost was costly. Repeated heating then losing the heat lost whilst switched off was also costly.
Your system might behave in a similar way in principle but as you have a small tank your demand for heat is different.
Heat loss is proportional to the log mean temperature difference. Therefore it will always be more efficient to only heat the tank when needed, not constantly. You either didn’t do your modelling correctly or you have since forgotten the result.When in uni we were doing mathematical modelling. One of the simple models was comparing heating into a storage tank. Based on the copper cylinder type normal in those days.
Basically the key to best economy was good insulation of the tank and leaving the heater switched ON to maintain the water temperature. The initial heating to temperature was the main cost, a thermostat to compensate for small heat loss through insulation was minimal. Of course, this was for a system where water was not being drawn out by taps, showers, dishwashers etc. And little need for reheating. If you are out all day or sleeping at night then that is where the savings were being made.
No insulation meant heat lost was costly. Repeated heating then losing the heat lost whilst switched off was also costly.
Your system might behave in a similar way in principle but as you have a small tank your demand for heat is different.
Edited by sospan on Thursday 27th February 18:50
Some interesting comments here.
We changed our controls earlier this year so we have better control of DHW heating.
We heat the water up to 65 degC in the morning before showers and then draw on it all day. We still have enough for showers at night but the water is obviously noticeably cooler, mainly as cold has been added to it during the day through hot water use.
We will turn the heating on if we want a bath in the evening.
We have noticed about a 5% reduction in gas use but can't be sure that this is due to the new DHW timings.
What I am amazed at is how quickly the tank warms up from being stone cold if we've been away.
Any observations would be interesting.
We changed our controls earlier this year so we have better control of DHW heating.
We heat the water up to 65 degC in the morning before showers and then draw on it all day. We still have enough for showers at night but the water is obviously noticeably cooler, mainly as cold has been added to it during the day through hot water use.
We will turn the heating on if we want a bath in the evening.
We have noticed about a 5% reduction in gas use but can't be sure that this is due to the new DHW timings.
What I am amazed at is how quickly the tank warms up from being stone cold if we've been away.
Any observations would be interesting.
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