Timed or internet-controlled thermostats for home heating/air conditioning systems have become quite popular for energy-saving reasons. In many households no one’s home for 8 hours a day, plus, in the wintertime when we’re asleep under all those blankets, we don’t need the house to be kept at 68. (This is assuming, of course, that it actually is cheaper to turn your heat down/AC up for those hours you’re not using it, rather than leaving it running so it doesn’t work as long when you do turn it back on. I understand that experts have done the calculations and shown that under typical conditions, it is.)
This morning, at the end of a shower long enough to nearly deplete my hot water, I started wondering: would the same thing be true for water heaters? I live alone and am gone for at least 10 hours straight each day. Would it be cheaper to turn off the water heater and let the water come to room temperature, and have it turn back on an hour before I get home, than it is to have it keep the water at 130 degrees all day? If so, why aren’t timed or internet-controlled water heaters more popular?
We shut off our water heater (more precisely, we set its temperature dial to “vacation”) whenever we go away for a week or more. Takes an hour or more for it to get the water hot after we get back and turn it back on. But I don’t think I’d bother shutting it off for half a day. The heat jacket on those things is pretty efficient.
(We also shut off the water by turning off the main water valve inside the house when we leave for vacation. Don’t want to risk coming home to a basement full of water.)
:eek: Are you me? I do the exact same thing. Worry is not so much a basement full of water, but a leak somewhere higher up in the house.
I leave a faucet cracked open somewhere in the house so that the piping can’t develop a vacuum as the water heater cools down. The pipes themselves would be fine, but without vacuum relief I think there’s the potential for buckling the tank if the hot water contracts enough as it cools down to room temperature.
To the OP: I can’t see how it wouldn’t be more efficient, unless the insulation is so good that there would be no significant heat loss over a typical 8 hour workday.
You can get a 240 volt programmable water heater timer (electric water heaters only). And with that, you can set it to make hot water for morning showers, then turn off the rest of the day and you would have residual warm water.
If you are using warm water (instead of hot) for dish washing, hand washing, and clothes washing, THAT can save a lot on the electric bill! Note an electric water heater can be 30% of an electric bill typically.
It depends on how long you’re gone. Since a water tank is a better holder of heat than a house, it’s almost certainly not worth it just for one day like it usually is with heat and AC.
A tankless heater only heats water when needed, so it’s already turned off all the time except when you need hot water. It doesn’t hold any heat in reserve like a tank, or a house, does, and so doesn’t leak any heat.
I’d question whether it’s more efficient to let the water cool down and then heat it back up to temp every day… it takes a LOT of energy to heat water, so it is probably more efficient to heat it up and keep it there over the course of the day- how often does your water heater really cycle on and off over the course of the day if you’re not using hot water? Mine cycles very, very infrequently unless I’m running the dishwasher, washing machine, or someone’s showering.
That said, it’s almost certainly more efficient to dial it down if you’re not going to be there for an extended period. I don’t have any idea where that break-even point is though- 3 days? 1 week? 9 days?
However, water cools off really slowly. I used to have my water heater timer turn on three hours per day. It cut on at 5:30 and off at 7 in the morning and evening. If I wanted a shower before bed instead of at 6:30 AM or PM it was fine. I just used less cold in the mix.
No, maintaining a certain temperature will always require more energy than just letting it cool. The hotter is it, the faster the energy is lost and the more you need to put in to keep it hot.
Wow … you use 30 gallons of hot water for just one shower?
I’d say you’ll not notice anything if you turn off your hot water heater during the day, except you’ll have to wait for the tank to warm up when you do get home.
Try this first: Step into the shower and get yourself all wet, then turn the water off while you soap up and scrub, then turn the water back on to rinse off. That’ll save you money on your electric and water bill. Work on trying to use only three gallons of hot water per shower.
I’m currently staying in a vacation rental which I think has a relatively small water heater. They also seem to have the temperature set low (probably for liability concerns) so I literally have the handle all the way to the hot side; it’s comfortable with 0% cold. Those two facts are probably why I’m using up almost the whole tank.
This. A hot water tank is, what, about 5 feet tall, and 3 feet across, and well-insulated.
Your house is maybe 12-30 feet tall, 40 feet across, and very mixed levels of insulation.
Sure, the temperature difference at the heater is higher, but not enough to make up for the vast difference in size.
If you’re gone for a season, turn off the hot water, but for a day, I doubt it’s going to be worth the trouble (though I will bow to anyone who does an actual calculation…)
That’s not what I was saying. I was saying that heating 55 gallons to say… 140 degrees would probably be less expensive to keep at 140 for 9 hours, rather than letting it cool to 95, and then heating it back up to 140 as fast as possible.
Of course it’s dependent on the insulation, ambient temperature in the water heater’s environment, etc…
Which is what Quercus and **lance strongarm **are also saying…
No, you are constantly losing energy to the surrounding environment, there is no way to avoid this as long as the water’s temperature is above ambient. Letting the water cool for 9 hours and reheating it will use less energy than keeping it at 140 for those 9 hours because the lower temperature reduces the loss rate.
It may not make much practical difference, but that doesn’t change the physics involved.
Correct, the higher the temperature difference, the greater the energy flow and loss.
However, the tank should be insulated and wrapped. This is actually really effective and would save far more money than flippin’ the power on and off. From the OP’s reply to my earlier post, I’m thinking a low-flow shower head is in order as well. If it’s a rental unit, then the landlord sure as hell doesn’t care.
Heat loss will be proportional to the delta T between the tank and the surroundings. Technically the log mean delta T, because as the tank cools the house warms up, but the house warms very little, so we can ignore that.
With that in mind, if I’m looking for efficiency I turn off the heater before my shower, leaving cold water in the tank when I’m done. That’s how I do it when I leave the house for more than a couple of days.