Guys, How long do you think an Electric H20 Heater needs to be turned off in order to save electricity. Obviously, I know if you go on vacation, there's no point in leaving the heater on. But is there any efficiency in turning it off for 8 hours - Or are your savings lost when you heat the water back up?
Saving electricity
- Thread starter rgood
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Bird
Rest in Peace
An interesting question. I never turn ours off unless I am turning off the water to the house. Am I wasting electricity? I don't know.
MossRoad
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I think a water heater blanket for an electric water heater will save more $ over an 8 hour time span than turning it off and no blanket.
Egon
Epic Contributor
If you are living in a cold area and the heat emanating from the water heater goes toward heating the house would it be considered a heat loss during the heating season?
thatguy
Elite Member
That is a good question.. I bet the only way to really get a good idea is to put one of the kilowatt meters on it and record usage for a few days.. If you find out it runs quite a bit between say 9am and 4pm OR 9pm and 5am (when hot water usage is probably pretty low) then you can calculate and see if you can save anything
Brian
Brian
thatguy
Elite Member
edited - double tap somehow
Highbeam
Super Member
Kill-a-watts work on 100 volt appliances only. Maybe spend a month manually flipping the breaker off at night and check your bill.
I would think that if I had a pan of water on the stove and maintained that at 120 for 8 hours, that would take more energy then heating it from from cold when I needed it - But I don't know the details on hot water heaters.
RonMar
Elite Member
I would say it probably has to be off quite a while. Some tank heat loss tables I have used for other calculations say a steel tank with 1" of insulation, filled with 120F water in 60F still air will loose about 25 BTU per SQ/FT per hour. A 50 gallon water tank has about 21.3 SQ/FT of surface area, so that is about 532 BTU of heat loss per hour. It takes 4000 BTU of loss to drop the tank temp on 400# of water 10F. So the tank would probably only be down about 10F in 8 hours. An electric heating element delivers about 3413 BTU per KW per hour, so a standard 4.5KW heating element would heat at a rate of 15,359 BTU, which would put the tank back up to 120F in about 15 minutes, at a cost of around 1 KW hour(multiply by your local power rate). If you use hot water in the morning and the tank warms to shutoff temp, it probably dosn't run again all day unless it is in a drafty unheated basement space. Most tanks also have more than 1 inch of insulation around them, and more is better in this case.
It should take about 1.56 hours for the 4500W element to heat a tank from 60F to 120F. That is a little over 7KW hours of energy(again multiply by your local rate). If your power rate is say 10 cents per KW/HR, then it would take 70cents to heat that tank of water from 60F to 120F. If not being used, and the tank only re-heats say 2.5 times a day at 10 cents per re-heat, you would have to turn it off for about 3 days to equal that 70cents to fully re-heat a tank that has cooled to room temperature. Under the above conditions, I would guess that any day after 3 days, you are saving about 25 cents per day... These numbers are very rough, so YMMV.
It should take about 1.56 hours for the 4500W element to heat a tank from 60F to 120F. That is a little over 7KW hours of energy(again multiply by your local rate). If your power rate is say 10 cents per KW/HR, then it would take 70cents to heat that tank of water from 60F to 120F. If not being used, and the tank only re-heats say 2.5 times a day at 10 cents per re-heat, you would have to turn it off for about 3 days to equal that 70cents to fully re-heat a tank that has cooled to room temperature. Under the above conditions, I would guess that any day after 3 days, you are saving about 25 cents per day... These numbers are very rough, so YMMV.
PA hayseed
Platinum Member
I won't qoute you any specifics, because I have none to give you. My grandfather (plumber) and my brother (plumber) both have taught me to wrap my pipes, wrap my heater, and install a little gray box, water heater timer. It isn't how long it needs to be off to save money, it really is how much are you paying to heat water 24 hours a day 7 days a week. The avg heater will kick on and off (depending on all sorts of variables) all day constantly heating the water to the same temperature whether you use it or not.
I heat my water twice a day, all year long. It has a manual override, so when I have company over and they take 30 minute showers I can turn the water heater on ...or off (depending on whether or not I care for the person).
I heat my water for 4 hours in the morning (wife and I hit the shower at different times), and for four hours at night. I set mine up to come on about 30 minutes before our day begins, and to shut off about and hour after we normally leave for work. I have it set to turn on about the time I leave from work to go home. We rarely use all the water, or the water gets cold. If it does, about 10 minutes will get you a new hot tank.
Wiring it up is easy, as you will already have electric running to an electric one.
Don't know if this long winded diatribe has helped or not.
Hee is a link so you can see what I am talking about. You can buy other versions of this if you choose. I also think you can get a better price than the one offered here. I just pasted this link cause it was the first one I opened with a pic. http://www.science-city.com/ligrboxinmow.html
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BobRip
Elite Member
It will save you money, but not a lot and it adds inconvenience. Ronmar's analysis was pretty good. However if you can time it so that the power is turned off before it fully reheats from your showers then you will save a little more since the average water temperature in the tank is lower and loss will be lower.
Definitely insulate the pipes, both the hot and cold. Touch the cold pipe when you have not run any hot water for a while and you will see that it is hot. You are paying for this loss. Also insulate the tank. I have a Marathon hot water heater and it has foam insulation. Also a life time tank warranty. It will hold the heat much better.
Losses to a heating space do add heat, but if you have a heat pump then it will heat 2 to 4 times more efficiently. Also the heat loss in the summer will add to your air conditioning bill.
I have used a timer for 20 years and finally disabled it because of the inconvenience and the Marathon water heater.
Definitely insulate the pipes, both the hot and cold. Touch the cold pipe when you have not run any hot water for a while and you will see that it is hot. You are paying for this loss. Also insulate the tank. I have a Marathon hot water heater and it has foam insulation. Also a life time tank warranty. It will hold the heat much better.
Losses to a heating space do add heat, but if you have a heat pump then it will heat 2 to 4 times more efficiently. Also the heat loss in the summer will add to your air conditioning bill.
I have used a timer for 20 years and finally disabled it because of the inconvenience and the Marathon water heater.
ctpres
Gold Member
Ronmar proves that this is the place of higher lerning. Wow I love this place.
--------------------------------------------------------------------------------Thatguy
"Kill-a-watts work on 100 volt appliances only."
True. But 220 is really 2 110's. If you wanted to you could use two Kill-o-watts. One on each 110 leg. Also using just one on one half of the 220 would give you a reasonabbly good answer. BUT Kill-o-watts will have a maximum wattage rating and I would guess that to be 1500 watts so you could only use it (one or two) if heater is rated at 3000 watts or less.
--------------------------------------------------------------------------------Thatguy
"Kill-a-watts work on 100 volt appliances only."
True. But 220 is really 2 110's. If you wanted to you could use two Kill-o-watts. One on each 110 leg. Also using just one on one half of the 220 would give you a reasonabbly good answer. BUT Kill-o-watts will have a maximum wattage rating and I would guess that to be 1500 watts so you could only use it (one or two) if heater is rated at 3000 watts or less.
Egon
Epic Contributor
There are "On Demand " units that will mostly eliminate the "Heat Lost" during no usage times.
RonMar
Elite Member
Bob touched on a good point. I didn't account for any plumbing losses in my example. It assumed that all the pipes connected to the hot water heater were insulated to the same standard as the tank. Any plumbing losses would greatly accelerate the heat loss from the tank.
The pipes do not have a lot of surface area compared to the tank, but they are probably copper, which is way more thermally conductive than the steel tank. A bare pipe connected to the top of a water tank will act like a heat pipe and and will have internal convection currents. The water cooled against the skin of the pipe being more dense will fall back into the tank. Warmer water from the tank will replace this falling cool water up thru the center of the pipe. This is a form of thermal siphon. It is also the same principal the engineers used to keep the perma-frost frozen under the heated alaskan pipeline without requiring any power...
Insulation is your friend when storing heat in water. That heat loss figure for 120F water in a tank with 1" insulation of 25 BTU/SQFT/HR drops to 12BTU/SQFT/HR with 2" of insulation. It drops to 9 BTU/SQFT/HR with 3" of insulation... Insulate, insulate, insulate. It is the biggest bang for the buck IMO.
The pipes do not have a lot of surface area compared to the tank, but they are probably copper, which is way more thermally conductive than the steel tank. A bare pipe connected to the top of a water tank will act like a heat pipe and and will have internal convection currents. The water cooled against the skin of the pipe being more dense will fall back into the tank. Warmer water from the tank will replace this falling cool water up thru the center of the pipe. This is a form of thermal siphon. It is also the same principal the engineers used to keep the perma-frost frozen under the heated alaskan pipeline without requiring any power...
Insulation is your friend when storing heat in water. That heat loss figure for 120F water in a tank with 1" insulation of 25 BTU/SQFT/HR drops to 12BTU/SQFT/HR with 2" of insulation. It drops to 9 BTU/SQFT/HR with 3" of insulation... Insulate, insulate, insulate. It is the biggest bang for the buck IMO.
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BobRip
Elite Member
I understand that some tanks have a check valve to stop the thermal siphon. I have no idea how well this works. Insulation as usual will help.
BobRip
Elite Member
There are "On Demand " units that will mostly eliminate the "Heat Lost" during no usage times.
I think the on demand is OK if you have gas. The electric takes a lot of electrical service to operate and will probably not allow several faucets to be used at one time. It would also require a big generator if you are running on one of these. Does anyone have one of the electric on demand units? How well does it work and what are the restrictions? My knowledge on these is only theoretical.
RonMar
Elite Member
A check valve on the tank outlet would stop the type of siphon loss I described, but you would need one on both the hot and cold water lines if both run upward from the tank. Heavy insulation will also stop the process, as the thermal siphon process is powered by heat loss/transfer.
You can also sometimes get siphon losses if the hot and cold are connected somewhere in the home(malfunctioning mixing faucet valve?). I recall reading about a product called a thermal lobster or hot water lobster. It is I believe a thermally actuated valve, that allows the siphon process to bring hot water to a sink and maintain the water temp at that sink so you have instant hot water. It basically connects the hot and cold lines together and allows the water to flow up the hot line to the valve. When it senses warm water, it closes and stops the process. As it cools it opens and again allows flow. Since plumbing is typically not as well insulated as the tank, it looses a lot of heat, so this type of constant availability instant hot water, although convenient, is very wastefull of heat(saves water though
).
buckeyefarmer
Epic Contributor
My house has a 240V KWH meter, and I suspect yours does also.
buckeyefarmer
Epic Contributor
Most Hot water heaters are 240V, 1ph, 2 wire. There is no neutral, so you would have to use a 240V, 1ph meter.
I cheat.
I've got a water-source ("geothermal" these days, I guess...) heat pump that uses a desuperheater to shuttle heat to the DHW whenenver it runs.
During the winter, when heat pump's running a lot, it will consistently keep the DHW tank at around 90 degrees. I also have off-peak billing.... so I turn on the water heater disconnect in the early AM, shut it off when I leave the house for work. Best of both worlds, I'm thinking! DHW pressure tank is also covered with 1" Armaflex, 80-gallon electric water heater purchased with heavy insulation package.
Oh- and in the summer, I can flip a switch for A/C.... (shhhh...whispering here...and if it's laundry day the system will take house heat and put it directly into DHW.) Never regretted the additional installation expense 23 years ago!
I've got a water-source ("geothermal" these days, I guess...) heat pump that uses a desuperheater to shuttle heat to the DHW whenenver it runs.
During the winter, when heat pump's running a lot, it will consistently keep the DHW tank at around 90 degrees. I also have off-peak billing....
so I turn on the water heater disconnect in the early AM, shut it off when I leave the house for work. Best of both worlds, I'm thinking! DHW pressure tank is also covered with 1" Armaflex, 80-gallon electric water heater purchased with heavy insulation package.Oh- and in the summer, I can flip a switch for A/C.... (shhhh...whispering here...and if it's laundry day the system will take house heat and put it directly into DHW.
) Never regretted the additional installation expense 23 years ago!
