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Gary_602z 11-15-2008 04:52 PM

Hot water heater electrical usage.
Hello There!
On a hot water heater where the upper and lower element are each 3380 watts at 204vac and total is 3380 what would be my kw usage if it ran straight for 1 hour? 3.380kw or double that?
Thanks in advance!

Also are both temp controls to be set at the same temp or slighty different?


micromind 11-15-2008 05:37 PM

A water heater that has two elements uses only one at a time. If the tank is cold, the top one will heat about 5 gallons of water quickly, then it'll transfer to the bottom one to heat the rest of the tank.

Both thermostats should be set to the same temperature.

In your case, if the heater was on for 1 hour, the power consumed would be 3.38 kilo-watt hours. if your power costs $0.10/kilowatt hour (KWH), then you'll pay 33.8 cents per hour of operation.

Note that the heater only consumes power when it's actually heating water. If the water is already hot, it consumes absolutely nothing.


Gary_602z 11-15-2008 05:55 PM

Thanks! I learn something new every day! I thought both elements ran together.


Gary_602z 11-16-2008 09:17 AM

Hello There!
I am Back!:thumbup:
A couple more questions. What determines when the upper coil comes on? Is it at a preset temp or is at so many degrees under what it(the upper element) is set at?
Would it be possible to run both elements at the same time? Can't you tell that I am about to MacGyver something?
Any links or info about temp rise with inlet temps,gph and wattages?

Gary (Building my first Rocketship)!:laughing:

Billy_Bob 11-16-2008 09:49 AM

The upper element has a different thermostat on it than the lower. When the upper thermostat detects that the water is colder than the temperature set, it connects the electricity to the upper element only.

When the upper thermostat reaches the set temperature, it switches the electricity to the lower element thermostat.

The lower element thermostat just turns on/off the lower element as needed.

In practice the lower element is the only element used. Rarely is the upper element used. If you are running out of hot water, set the temperatures higher or get a larger (more gallons) water heater.

You can't get both elements to work at the same time because you would need much larger wiring and a higher amperage rated thermostat/connections on the upper thermostat, larger wires going to the water heater, and a larger breaker.

Water heaters are designed this way intentionally so there will not be a big surge of electricity used all at once. Something to do with everyone taking a shower at the same time in the morning and there being a big surge of electricity needed by the power company to reheat all that water!

Gigs 11-16-2008 06:16 PM


Originally Posted by Gary_602z (Post 185772)
Would it be possible to run both elements at the same time? Can't you tell that I am about to MacGyver something?

If you aren't talking about a home installation, and instead some crazy project, then yes it is possible to run both at once. Like was mentioned, you'll need bigger wires and a breaker that is twice as large.

An exploding water heater can easily kill you. Be safe.

Gary_602z 11-16-2008 07:51 PM

Thanks Guys!
I am trying to help out a buddy with a infloor radiant heat system in his garage. He didn't really research it much when he put it in and just put in a 40 gallon heater. I am just trying to get a little more umph out of his current system,but am not going to run bigger wires (already run in EMT).
I have a hard enough time convincing him to finish his insulation first!

Thanks Again!

kennzz05 11-16-2008 08:04 PM

:)thats what they make boilers for. im sure even a gas tank couldnt handle that load bet he will replaceing elements and tstats on a reg basis could look into tankless heaters but there expensive mythbusters exploded a 40 gal tank by overheating it and removeing the p/t valve it shot 500 feet in the air and was airbourne for 13 seconds anotherone leveled a 10x10 wooden shed they built as it shot thru the roof search on youtube perhaps you could put a timer on the pump and cycle it every five min to alloy the tank to heat he did make a manifold system on the pipes correct

Gary_602z 11-16-2008 08:25 PM

Yeah! Like I said he didn't research it and somebody told him he could heat it with a hotwater heater. He was/is on a limited budget also.
So for now we are just trying to get the most out of it,but he keeps turning it off at night because he is afraid of his electric bill. I tell him that he has to keep a steady heat to it to warm the mass of concrete.
Oh well at least we can pick our friends unlike our relatives!:laughing:


Gigs 11-16-2008 09:30 PM

Hrm. Well since you have a lot of thermal mass in that concrete floor, I'd say you have a good start to a closed loop solar heating system. Have it heat the concrete and water during the day, then at night it'll stay warm for a long while.

Sell the water heater and look into that maybe. :)

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