Should I keep water heating turned on all the time?

yygaurav · 19-01-2024 11:57pm #1

Hi

We have 3 zone heating in our house.

Zone 1: Heating downstairs - connected to nest

Zone 2: Water - connect to nest

Zone 3: Connected to EPH timer based system ( 3 zone, but 2 zone are not connected since i got nest installed)

For water we are using nest time schedule to turn on/off and specific times but we find it frustrating as water heating schedule does not match our life style so we have to turn on water on demand during the day. We have been recommended that we should keep the water heating on all day and there is a thermostat installed on the water cylinder which will only heat water when it drops below the thermostat specified value ( currently set to 65 degrees)

Is this correct? Should we keep water on all day?

Thank you

10-10-20 · 22-01-2024 2:38pm

Hi! You could leave it on all day if you wanted to but it's not usually recommended that the water be left on all day unless there is a specific demand all day. To leave it on all day would be inefficient and your bills would be considerably higher than they are now. Normally you would have the timer heat the water before you need it, so perhaps two schedules: one in the morning before showers and maybe one in the evening before washing/baths. You could set longer heating periods in each of these windows (such as 3hrs) and let the thermostat do it's job and turn off the boiler once it's up to temp.

Hope it helps.

Squatman · 22-01-2024 2:53pm

https://www.boards.ie/discussion/comment/121654465#Comment_121654465

Is this statement factual or speculative? If the heater is active continuously throughout the day, the temperature is likely to stabilize closer to the setpoint. In contrast, if the heater operates intermittently, it has to respond to peaks in demand, leading to higher current draw for shorter periods. Keeping the heating on throughout the day would result in more frequent modulation but for shorter durations. There's no definitive answer; it likely depends on demand and temperature setpoints. The best approach is to experiment with both methods and observe the results.

In my case, the heater is on all day, and I can be confident that the hot water temperature is sufficient to eliminate bacteria at any time, day or night. Relying on timers may result in tepid water during certain periods.

10-10-20 · 22-01-2024 3:27pm

https://www.boards.ie/discussion/comment/121654578#Comment_121654578

I'm not in full agreement. Keeping a cylinder heated causes increased loss of energy as the cylinder is being constantly maintained at a higher temperature (heat flux), possibly unnecessarily. Additionally, cycling the boiler outside of times of demand once the stat has called for heat (with reasonable hysteresis) is creating additional losses within the system (pipework, pump, heat exchanger).

Hence my statement "unless there is a specific demand all day". If there is a continuous demand then leave it on, fine; otherwise only have it on in and around the crucial demand times. It's basic physics.

Squatman · 23-01-2024 2:23pm

https://www.boards.ie/discussion/comment/121654777#Comment_121654777

the losses in the system exist if the heating is on or not, I would expect the delta in flux at 50 degrees or 60 degrees would be minimal. open to correction, obviously the higher the water to ambient temperature delta, the higher the flux, but as the temperatures are so low to begin with, I hypothesize that the difference in flux would be minimal/academic. So the next point is the insulation quality, or the ability of the system to maintain the heated water, if that is well insulated, I would recommend all time on (as is the case for my system).

if your aim is efficiency, and not water temperature then timer, 1 hour per day for the heater. best case you will have tepid water for a short period. if you need hotwater thru the day, a well insualted water tank, on a thermostat is the only gig In town... .its basic physics 😴

coylemj · 23-01-2024 2:35pm

There is no such thing as perfect insulation. If there was, it would make no difference in cost if you kept the immersion on all day. And the amount of energy you'd consume would be in direct proportion to the amount of hot water you draw i.e. there would be no wasted energy.

But the absence of perfect insulation means that if you leave the immersion permanently on, you will be losing heat and that evaporating energy is money wasted. When left on, every time the thermostat cuts in to top up the heat, it's replacing energy which has floated into the ether, along with your money.

Calahonda52 · 23-01-2024 2:35pm

on this "its basic physics 😴" The longer the tank is at 65 +/- the stat spread, the greater the heat loss.

If the tank its only heated as required. then as it cools the heat loss delta T is less so less heat loss

10-10-20 · 23-01-2024 2:50pm

https://www.boards.ie/discussion/comment/121659636#Comment_121659636

So I'll respond with this: it's like boiling a kettle all day long for two cups of tea in a day... putting aside the amount of steam caused - it's the same point about energy loss. You only needed the water boiled for two points in time, so why suffer the loss of energy all day?

This example is abstract I know - but have a look at the spec for a Burko boiler - they have a sustained loss of 1kW per hour, every hour; while a 2.8kW kettle boiled for 5 mins has a consumption of 233Wh for that boiling session. If you don't need the boiling water after that point then there is no need to keep the water boiling. I see it the same way with a boiler system and cylinder if you count all of the losses into the loop then it's inefficient to have the water continually heated up to 65 degrees C outside of the demand time.

Lenar3556 · 23-01-2024 4:20pm

My own view would be the benefit/convenience in having hot water available at all times outweighs the energy savings of adding timed periods top of the temperature controls.

Modern cylinders are very well insulated and have published loss factors per 24HR’s at a given temperature. Most are less than 1.5KW/h @ 60oC and you have to consider that this is being lost into the house as additional space heating - not simply discarded outside.

There will be some additional boiler cycling, I agree - but I think it’s a small price to pay.

Squatman · 23-01-2024 8:52pm

https://www.boards.ie/discussion/comment/121659887#Comment_121659887

yea, i agree re the boiling the kettle analogy, provided boiling water is the desired state. and if it is, then on all day is the way to go, but if the water temp drops to 5 degrees for example, in a 3 hour timed heater due to the volume in the hot water cylinder, it may only rise to 40 degrees. and that too might be desirable to some,... note, in you 1kW per hour example. on a thermostat controlled modulating system this will take several hours to cost the 30ish cent of the 1kW charge

10-10-20 · 24-01-2024 11:02am

Anyway, I think that the heel of the hunt is that a decision around heating water is best made by looking at the demand.

I'm a bit of an energy zealot so I have a setup where I have two main demand times: around 7am to 8am and then 5pm to 8pm. I setup the boiler to come on every weekday at 05:30 to meet the initial demand, then I have a timer and stat on the tank (well, it's Home Assistant and some temperature sensors) which will only boost the tank between 8am and 7pm and only if the temperature drops below a set-point.

My reason for this? I have a 13m pipe-run between the boiler and cylinder (26m round-trip - dumb previous owner) so the thermal losses on that pipe alone are significant (in addition to the 5L volume of wasted water).

Anyway, always fun to compare notes.

Squatman · 24-01-2024 4:36pm

https://www.boards.ie/discussion/comment/121664136#Comment_121664136

would you switch it for a month for brass tacks, would be good to see what it costs from someone with their head screwed on

Should I keep water heating turned on all the time?

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