Is it best to turn a hot water system on and off or leave it on continually?
Image by gordontour
Tengboche, guest house
Question by ST K: Is it best to turn a hot water system on and off or leave it on continually?
We are running a 125 litre hot water heater for only two people. Its 15amp and single element I think. When we had solar heating, we got into the habit of turning the booster on and off accordingly. I’m wondering now, if we are energy saving by turning the current system off during the day and only flicking it on at night for a time? Or would it work out less expensive to let the thermostat regulate a permanent hot water temperature and in so doing, be using less energy overall? Its a balancing or juggling act I know but over a period of time, which approach makes more sense as far as costing less in power? Hot water usage is generally fairly conservative too and we don’t really need the scalding temps when its on all the time, even in the middle of winter. (Thermostat not adjustable)
Give your answer to this question below!
6 Responses to Is it best to turn a hot water system on and off or leave it on continually?
Leave a Reply
I think its best to leave it on, because if you turn it off, the water will get cold again and then take more energy to heat it up again… just a thought.
designerista
December 13, 2013 at 4:17 am
leave it on. that way you don’t have to keep reheating the entire tank. make sure you insulate the tank and the hot water pipes if you can. they also have a circulation system now that supposedly saves money and gives you instant hot water at all the faucets. i have seen it at lowes.
lmcmmason
December 13, 2013 at 5:14 am
you use less energy leaving it on……….. period. Any storage device uses less energy to maintain temperature. An on demand water heater is a different story.
lowracer1
December 13, 2013 at 5:51 am
this one actually sounds good for the energy company you use. my neighbors called srp and got on a time of day savins plan which they can help you set a program for t-stat, when to do cloths, high efficent light bulbs,& your water heater. it also depends on the volume of water you are using in one shot.
hotrod
December 13, 2013 at 6:40 am
Turning it off when you don’t need it, and turning it on when you do need is will save money.
The heater loses heat fastest when the temperature difference between the water inside and the air outside is the greatest. The hotter it is, the faster it loses heat.
The heater has some kind of set point…and you say it’s “scalding” so lets say it’s 140F. The air around it is 70F, so you have a “delta-t” or temp difference of 70F. There is a lag between when the heater turns on and shuts off. Let’s guess…and say your set point if 140F, and the thermostat turns it on at 136F, and heats till it’s 140F.
The minute the element goes off, the water starts losing heat…it goes from 140F to 139F faster than from 139F to 138F, and so on…the greater the temp difference, the faster the loss.
The heater will turn on several times per day, heating it back up. If you just let it fall, and then turn it on and heat it all the way back, it will take less energy. The longer it is off, the more you will save.
As the delta T become less, the rate of loss becomes less. Finally, you reach 0 delta-t, and have no loss at all.
For some reason, this idea that it will take more energy to “heat it all the way back up” is a popular, yet totally wrong idea. When you leave it on when you don’t need to, it’s losing heat at the highest possible rate, constantly. It does not take more energy to heat it all the way back, as it does to keep it hot all the time.
This is a law of physics, and public opinion won’t change that!
roadlessgraveled
December 13, 2013 at 6:53 am
Get a timer for the immersion heater fitted and set the boost for about two hours before you get in from work, ie after the solar has has chance to work on the cylinder for as long as possible.
This way if the solar has heated the water to 60*C then the thermostat inside the immersion heater will keep it off.
If the solar has heated the water to 30*C then the immersion heater will top up by 30*C, this is assuming that both solar and immersion heater are set for 60*C.
DON’T leave the immersion heater on all day. Your wasting your money and over-riding the solar system.
greensystemsuk
December 13, 2013 at 7:25 am