Turning off electric hot water heater when not home?

[Ryland]

even if it does retain most of it's heat there is no reason that it needs to come on after you used your hot water for the day, it would be like turning your tea kettle back on after you pour your tea, if you did that, even with a well insulated tea kettle people would say you were kind of dumb, so why have your water heater automatically come on after you've taken a shower and gone to work?

I have yet to hear of someone that hasn't seen a noticeable drop in there electric bill after installing a timer.

[fshagan]

Originally Posted by Ryland

even if it does retain most of it's heat there is no reason that it needs to come on after you used your hot water for the day, it would be like turning your tea kettle back on after you pour your tea, if you did that, even with a well insulated tea kettle people would say you were kind of dumb, so why have your water heater automatically come on after you've taken a shower and gone to work?

I have yet to hear of someone that hasn't seen a noticeable drop in there electric bill after installing a timer.

Your analogy falls apart in that an electric water heater is more like a thermos than a teapot.

It takes a certain amount of energy to raise the water a degree ... 2.42 watts per gallon. If you have to raise it 10 degrees, it doesn't matter if the heater comes on ten times to raise it one degree, or if it comes on once to raise it ten degrees. You use the same energy to recover the 10 degrees of heat you lost.

If you are getting standby losses through the jacket and save money by turning it off for 8 hours, you should definitely take the other, cheaper measures anyway. No matter when you heat the water, the heat loss is still happening. There's a good chart with formulas and facts at this PDF file link

Here's a quote from another website:

Use a timer on older electric heaters. A $40 timer can automatically turn off an electric heater when you go to work, then back on right before you come home, off after you go to bed, and on again right before you get up. These don't save as much money as you'd expect, though. That's because a typical electric water heater only runs about three hours a day anyway, and modern energy-efficient water heaters run only 1.3 hours or so. Standby losses (how much heat the tank loses by just sitting there) aren't that great, especially for modern heaters. (In fact, if your heater was made after 1998, it's probably not worth using a timer at all.) And even with a timer you'll still have standby losses as soon as you leave for work and after the tank shuts off for the night. A timer for an old (pre-1998) heater will save about 25kWh/mo. for a family of two using 40 gallons a day with the heater off four to six hours a day, but only 14kWh/mo. for a family of four using 80 gallons a day. (Florida Extension Service) (See below about how to install a timer.)

From http://michaelbluejay.com/electricity/waterheaters.html

You pay for electricity by the kWh, so if you are paying .08 per kWh, your monthly savings with a newer heater is only 1.12 per month. A $40 timer has a payback of about 3 years, and much longer if you pay an electrician to put one in ($80 to $120 in my area).

There is a point where turning it off will save money even with a well insulated tank, but that shouldn't be within 8 hours. If your friends are saving money over that short a period of time they still have a great opportunity to save money (and energy) by insulating the tank and pipes.

[bhazard]

"The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at 60°C (140 °F) and distributed such that a temperature of at least 50°C and preferably 55°C is achieved within one minute at outlets."

[ttoyoda]

Your analogy falls apart in that an electric water heater is more like a thermos than a teapot.

Well somewhere in between, but closer to the teapot. The thermos does not have copper pipes sticking out thru the vacuum jacket.

If you have the parts for free to turn the heater off sitting in your junk boxes, it makes sense to do so. If you have to buy them, then do a payback calculation.

[fshagan]

Originally Posted by bhazard

"The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at 60°C (140 °F) and distributed such that a temperature of at least 50°C and preferably 55°C is achieved within one minute at outlets."

Yep, and in the US, many local codes require water heaters to be set at no more than 120°F (or 125°F). The state of California has a requirement for that temp at all nursing homes, for instance.

Many codes waive the lower temperature if anti-scald mixing valves are used.

[fshagan]

Originally Posted by ttoyoda

Well somewhere in between, but closer to the teapot. The thermos does not have copper pipes sticking out thru the vacuum jacket.

Exactly ... which is why the first thing you should do is minimize heat losses! Fixing a dripping hot water faucet will save you more than a timer, as will insulating. But if the timer is free ... then its a no brainer.

I shudder when I see people spend $5,000 for a tankless water heater to save $130 a year on hot water. A lot of energy saving projects are that way, and that's fine if you want to spend the money. But for most of us, we should do the "biggest bang for the buck" stuff first.

[ttoyoda]

Minimize, sure, but with those copper pipes sticking out, there are serious limitations on how much you will be able to reduce the heat loss.. The best you can do is to insulate the inlet all the way to where the water pipe comes into the house, and the insulate the outlet pipe till it goes into a wall.. That is still not very good.

I shudder when I see people spend $5,000 for a tankless water heater to save $130 a year on hot water. A lot of energy saving projects are that way, and that's fine if you want to spend the money.

Absolutely agree with you here. But making a timer for water heater should cost very little. I got a lot of fuji relays, 3 pole, 52 amps at 240 volt rated, with 120 volt coils, for free at the scrap yard. How much could they be surplus? Here is a brand new one with reasonable ratings for 13 bucks.
http://search.digikey.com/scripts/Dk...name=PB1007-ND
Add to this a inexpensive programmable electronic lamp timer for $15, to run the relay, a metal box, and its done.

[fshagan]

Originally Posted by ttoyoda

Minimize, sure, but with those copper pipes sticking out, there are serious limitations on how much you will be able to reduce the heat loss.. The best you can do is to insulate the inlet all the way to where the water pipe comes into the house, and the insulate the outlet pipe till it goes into a wall.. That is still not very good.

Thermal traps are the order of the day, with insulation extending to the thermal trap. That reduces the radiation losses dramatically. Some heaters incorporate thermal traps into their instructions.

A thermal trap can be thought of as an upside-down sink trap; after exiting the water heater, loop the pipe down below where it exits the water heater by 6 - 12", then back up. Insulate. Heat rises, so the hot water from the tank will only go up into the pipe to the top of the "trap" you just plumbed. Its amazing how much difference you can feel between the portion of the pipe between the high point and the heater and the portion after the high point. You will save more doing this than installing a timer, but as with a timer, the cost gets too high for reasonable payback unless you are doing the work yourself.

[ttoyoda]

Thermal traps are the order of the day, with insulation extending to the thermal trap. That reduces the radiation losses dramatically. Some heaters incorporate thermal traps into their instructions.

That is very clever. Thanks for the info.

[COMP]

Originally Posted by fshagan

Your analogy falls apart in that an electric water heater is more like a thermos than a teapot.

It takes a certain amount of energy to raise the water a degree ... 2.42 watts per gallon. If you have to raise it 10 degrees, it doesn't matter if the heater comes on ten times to raise it one degree, or if it comes on once to raise it ten degrees. You use the same energy to recover the 10 degrees of heat you lost.

If you are getting standby losses through the jacket and save money by turning it off for 8 hours, you should definitely take the other, cheaper measures anyway. No matter when you heat the water, the heat loss is still happening. There's a good chart with formulas and facts at this PDF file link

Here's a quote from another website:


From http://michaelbluejay.com/electricity/waterheaters.html

You pay for electricity by the kWh, so if you are paying .08 per kWh, your monthly savings with a newer heater is only 1.12 per month. A $40 timer has a payback of about 3 years, and much longer if you pay an electrician to put one in ($80 to $120 in my area).

There is a point where turning it off will save money even with a well insulated tank, but that shouldn't be within 8 hours. If your friends are saving money over that short a period of time they still have a great opportunity to save money (and energy) by insulating the tank and pipes.

cool link