Turning the hot water off to save energy

December 24, 2011 2:51 AM

Can I save energy by turning the hot water off?

So, my family and I went away for 5 days this week, and the morning of departure (Monday) I turned the hot water off at the mains to save energy/money. We returned on Friday, and after having the hot water switched off all that time, on Friday night the water was still warm enough to have a comfortable shower. I turned it back on on Friday night, and this morning (Saturday) it was as hot as ever - ie it had completely heated up overnight.

So I'm thinking, why wouldn't I just turn the hot water on overnight, and then turn it off for 5 days, and then turn it on for a night again, and then off for 5 days, etc? Will I save energy and money by doing this? Is there a flaw in my logic?

Some extra info:

- I live in a sub tropical climate and it's summer here (Newcastle, Australia)

- The hot water system is electrical rather than gas

- The hot water tank is pretty big...

Some have argued that the energy that the system will expend getting the water back up to temperature will possibly equal the amount of energy saved... but I don't know if I buy this.

Anyone got any informed thoughts about this?

posted by saturn~jupiter to Home & Garden (12 answers total)

If you turn it off while you're home, you will quickly use up the water that has been heated and will only have cold water left. The reason it worked while you were away is because no one was there using water from the hot water heater. (Unless your hot water tank is VERY large and you also never shower.)
posted by anaelith at 3:01 AM on December 24, 2011 [3 favorites]

Also, legionella.
posted by anaelith at 3:03 AM on December 24, 2011 [3 favorites]

The energy lost from storing water at temperature in a modern, well-insulated hot water tank is pretty low. You can work out the calculations for yourself. If you really want to avoid that, what you want is a tankless water heater, not a manually-cycled one.
posted by lantius at 3:10 AM on December 24, 2011 [2 favorites]

The only reason the water was warm when you got back is because no one had been using any. If you don't turn your hot water on while you're home, you've probably got enough capacity for two or three showers, max.

However, there probably is a way you can save some money here. When I was in law school, I lived with a family who had signed up for their utility's time-shifting plan, where power was like $0.02/kWh from 9PM to 6AM and on weekends, and like $0.12/kWh the rest of the time. They had their hot water heater set to run overnight and shut off just before 6AM. We all had enough hot water for showers, but only just, and you really wanted to get yours done in the morning.

Even if your electric company doesn't offer something like this, you can still save money by not running the thing 24/7. Even just setting it to run twelve-on/twelve-off would cut its consumption significantly.
posted by valkyryn at 3:25 AM on December 24, 2011

My parents have wired theirs on a 24 hour cyclic timer. Two times a day (times when they normally use hot water for showers or dish washing) the hot water heater kicks on and warms the water in the tank, and then about an hour later it shuts off. Mom said that all other things equal, it has saved them about US$40 a month on the electric bill, and that's at some of the best rates in the country.

Here is an instructable to follow if you feel comfortable doing the wiring. You're not crazy for wanting to save electricity, and this is a great way to do it.
posted by deezil at 3:28 AM on December 24, 2011

If it was still hot enough to take a comfortable shower after five days, I would guess that when it's just sitting idle for relatively short periods and no one is drawing hot water from it, it's not using a lot of energy. So in the grand cosmic scheme of things, you can probably save some energy this way, but there are probably more convenient ways to save more energy that won't involve you taking a cold shower because you forgot to turn the hot water back on.
posted by Kid Charlemagne at 3:34 AM on December 24, 2011 [1 favorite]

Response by poster: "is there a flaw in my logic?"

...clearly YES! obviously the water wouldn't stay warm if we were using it... thanks for pointing this out to me, I feel a little foolish for not thinking of this obvious factor. however, I am not a daily shower-er, so I still think it could work.

thanks for weighing in, peeps.
posted by saturn~jupiter at 4:25 AM on December 24, 2011

If you use the hot water and empty the tank, heating up the new batch of water is not different than if you turned off the water heater and heated it up for the first time.

A common thing where I live (Florida), is for people to install timers on their electric hot water heaters. Let it run for only 3 hours a day. People definitely see energy savings by doing this.
posted by Flood at 4:56 AM on December 24, 2011

In the long term, if you don't use a great deal of hot water, you might save money by having a gas powered water-on-demand boiler. I have one of these: it takes a few seconds for the water to start coming through hot, but once it does I can have full mains power hot water whenever I want for as long as I want. Three baths in a row? No problem! No baths for a week? Costs nothing!

Gas heating is cheaper than electric too, or at least it is where I am.
posted by emilyw at 7:04 AM on December 24, 2011 [1 favorite]

I turn my hot water way back when I'm away. In your case, turn it off 8 hours or so before you leave for more than a day. The timer sounds like a great idea. And, since it's a large tank, turn it down a bit - no need to get it really hot.
posted by theora55 at 7:12 AM on December 24, 2011

The warm water after 5 days shows that your water tank is well insulated. It wouldn't have taken much extra energy to keep the water at full heat, because the tank holds energy so well. It's a small expense compared to heating up cold water after you use the hot.
posted by scose at 8:18 AM on December 24, 2011

"Some have argued that the energy that the system will expend getting the water back up to temperature will possibly equal the amount of energy saved... but I don't know if I buy this. "

Don't buy it; heat gain and loss don't work that way.
posted by Mitheral at 11:23 PM on December 24, 2011