# Powering Electric Water Heater w/Generator



## thinkxingu (Oct 4, 2010)

OK, so I recently installed an interlock kit on my main panel (no room for transfer switch/wanted access to all circuits) and I'm wondering what the 411 is on running an electric water heater.  

1. I've got a 5500 watt genny; am I right in assuming that, as long as I'm not running many other things, that it'd be ok to run my water heater?  
2. Also, does the h20 heater always pull 4500 watts or only upon turn-on?
3. Would it be best to keep the h20 heater off and only run at night/when needed or would it be best to run continuousally to maintain the temp?

Thanks,

S


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## vvvv (Oct 4, 2010)

thinkxingu said:
			
		

> OK, so I recently installed an interlock kit on my main panel (no room for transfer switch/wanted access to all circuits) and I'm wondering what the 411 is on running an electric water heater.
> 
> 1. I've got a 5500 watt genny; am I right in assuming that, as long as I'm not running many other things, that it'd be ok to run my water heater?
> 2. Also, does the h20 heater always pull 4500 watts or only upon turn-on?
> ...


2-yes
3-if u can coordinate ur hot water needs with the heater u can save some. heater only experiences standby loss when water is hot
1-goes to theory, but i run a mini oven & exhaust fan on same plug & when the oven heats, the fan slows down- i can hear it


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## thinkxingu (Oct 4, 2010)

~*~vvv~*~:
     What do you mean coordinate hot water needs with heater?  Do you mean to only run it when I'm using hot water?

S


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## nate379 (Oct 4, 2010)

You would have to run that just on it's own, as you would not have enough generator for anything else really.  Maybe a couple lights, but that's it.

Run the heater enough for whoever to take a quick shower and then shut it off.


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## thinkxingu (Oct 4, 2010)

It sounds like I should run it overnight to re-heat whatever was used.  I have a 50-gallon, and we had warm water the last time we lost power for two days.  I was just thinking that it would take less power to maintain water at temp than to re-heat after cooling down, but it sounds like it's all-or-nothing as far as power draw.  Of course, it would take less time to re-heat a small amount of new, cool water than to re-heat both cooled down water and new, cool water.

S


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## BrotherBart (Oct 4, 2010)

Yep it is all or nothing. I have a Blue Line power monitor. The house usually is running at half a Kwh or so during the day and anytime that water heater kicks the meter goes straight to over five Kwh until it shuts off. You would knock a five thousand watt generator to its knees.


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## thinkxingu (Oct 4, 2010)

Bart, that would only be if I was running other things.  At night, what's the draw--a couple watts for displays and the fridge kicking on once or twice?

S


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## nate379 (Oct 4, 2010)

All depends on the fridge.  Mine seems like it's almost always running.  One of them fancy $2300 digital display opens your beer for you units.


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## Highbeam (Oct 4, 2010)

When using my genset with interlock I shut off the water heater and hot tub. The fridge and freezer cycle and are on different "legs" of the panel so all is well. The water heater certainly can be powered by a genset through an adequately sized generator circuit that matches or exceeds the circuit rating of the water heater circuit but you need enough balls from your genset. I would be okay running a 4500 watt load from a 5500 watt genset since the water heater is a resistive 240 volt load with no big surge at startup. Your 5500 is rated continuous at 5500 right? None of this 5500 watt surge rating business? Be sure that other devices with sensitive electronics are not hooked up just in case you get a voltage dip.


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## thinkxingu (Oct 4, 2010)

Highbeam,
     The generator's rated at 5550 running watts and 8250 start-up.  If running the water heater, only the fridge and displays, etc. would be running (at night/morning =  no lights, tv, computer, etc.).  In talking to the local inspector, it sounds like it's all about managing usage when using a smaller generator.

NOW: what's the largest generator I could run with the 30 amp box, breaker, and 10 awg wire I used?

S


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## ROBERT F (Oct 5, 2010)

If the water heater was drawing on both elements at the same time, and the fridge's compressor went to start up, you would be short on power for just long enough to do damage to the fridge over time.  might not happen the first time, but repeat a few times and ????


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## thinkxingu (Oct 5, 2010)

Two things:

1. I've read that water heaters only use one element at a time, which is regulated by the thermostats.
2. My heater says 3,800 is the draw for each element.

S


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## maverick06 (Oct 5, 2010)

the water heater wont have a *peak* draw like a ac motor has, just a heavy load. 

If you just heat up the tank overnight it will be plenty good. i have my home water heater on the "off peak" meter, so it is only energized from about 6pm until 6 am. But if you go to take a shower at 5pm, the water is still nice and hot since it hasnt been used much durring the day. 

I looked into this, and told my wife that if power is out, so is the hot water... my generator wont run that, the AC or the stove... everything else is fair game.


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## vvvv (Oct 5, 2010)

thinkxingu said:
			
		

> ~*~vvv~*~:
> What do you mean coordinate hot water needs with heater?  Do you mean to only run it when I'm using hot water?
> 
> S


turn it on 1 hr be4 using hot water, then turn it off be4 u using hot water. drain the tank from usage & leave it full of cold water until next episode= minimal standby heatloss


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## vvvv (Oct 5, 2010)

thinkxingu said:
			
		

> Two things:
> 
> 1. I've read that water heaters only use one element at a time, which is regulated by the thermostats.
> 2. My heater says 3,800 is the draw for each element.
> ...


3800 X2 = 7600 for cold water startup, i think


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## Highbeam (Oct 5, 2010)

3800 times two elements would be 7600 watts at 240 volts would be 31.66 amps. All of the water heater circuits that I have seen are fed by 30 amp breakers. How can you know if both elements fire at once? It would seem as though they can't without blowing the breaker.

If both elements are on and you want to run them from a genset then you would need at least 7600 watts of honest generator capacity and you would need more than the 30 amp generator circuit can provide. As such, unless you can disable or be certain that only one element fires at a time, you can't run that water heater with the 30 amp generator circuit.

Given that your water heater circuit has a 30 amp breaker and that your generator circuit has a 30 amp breaker AND if you can acquire a genset that can make the full 7600 continuous watts I would try it. I would shut off all other circuits including the fridge during this loading. Your fridge will stay cold overnight if you don't open the door.


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## Highbeam (Oct 5, 2010)

If having hot water at all times is this important to you, perhaps it is time to switch to a gas water heater? 

I've just decided that we won't have hot water during an outage and if I need it really bad then I can go out into the RV and fire up the 6 gallon LPG water heater, furnace, and take a shower out there. It is good to have a second home that needs no utility power.


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## Cowboy Billy (Oct 5, 2010)

Highbeam

Thats what we are planing on doing at the farm for a outside shower in the summer. My brother found a tank less propane hot water heater for $150 on epay. But I haven't got the wood cut to build it yet.

Billy


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## thinkxingu (Oct 5, 2010)

As mentioned, it's not a huge deal since the water stays warm for a few days without power anyway.  I was just thinking that since it's all hooked up, why not keep the h20 hot?

S


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## vvvv (Oct 5, 2010)

critical q= caN THE WHEATER SLOW DOWN THE GENERATOR? i know a motor can but dunno if electric elements can.......& i'm betting they cant.................ya , overloaded my gen with a circ saw   but it didnt work under cutting load== bla bla===it will work, no prob..................any bets?    1-1 odds


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## begreen (Oct 6, 2010)

No, both elements do not come on at once. The upper will come on if the tank is cold. Lower if it is warm.


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## thinkxingu (Oct 6, 2010)

Right, so 3800 watts on a 5500 watt generator should be no problem.  As for gas, that's out: I have it at the street, but I'd never recoup the costs associated with changing heating systems.  The question is still: what would be the best time to run the h20 heater?  At night, after using it, just leave it on because keeping it warm doesn't take as much energy as heating it up?

S


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## vvvv (Oct 6, 2010)

thinkxingu said:
			
		

> OK, so I recently installed an interlock kit on my main panel (no room for transfer switch/wanted access to all circuits) and I'm wondering what the 411 is on running an electric water heater.
> 
> 1. I've got a 5500 watt genny; am I right in assuming that, as long as I'm not running many other things, that it'd be ok to run my water heater?
> 2. Also, does the h20 heater always pull 4500 watts or only upon turn-on?
> ...


dunno where the 4500w came from? last i worked on heater there were 2 elements & each had its own thermostat, i assume that when full of cold water both elements will burn because each thermostat will be calling for heat


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## vvvv (Oct 6, 2010)

thinkxingu said:
			
		

> Right, so 3800 watts on a 5500 watt generator should be no problem.  As for gas, that's out: I have it at the street, but I'd never recoup the costs associated with changing heating systems.  The question is still: what would be the best time to run the h20 heater?  At night, after using it, just leave it on because keeping it warm doesn't take as much energy as heating it up?
> 
> S


standby heatloss from water heater can only happen when full of hot water. if tank is cold it loses no heat & heating cold tank uses no more energy than constantly reheating warm water. I still think heater will work if both elements fire at the same time but i aint sure. member Cozyheat is an electrical engineer ithink


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## kabbott (Oct 6, 2010)

~*~vvv~*~ said:
			
		

> thinkxingu said:
> 
> 
> 
> ...



I am pretty sure that when the top thermostat comes on it cuts the bottom element off. That lets the top element heat up top half of tank
so you get your hot water back faster. I 'think' my top element is 4500 watt but my bottom element is only 1500???

Kris


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## thinkxingu (Oct 6, 2010)

The 4500 was quoted somewhere online as the power required for a hot water heater, but my actual heater says 3800 top and bottom.  Looks like there was an option to have 3800 bottom and 4500 top.

S


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## Cowboy Billy (Oct 7, 2010)

thinkxingu said:
			
		

> Right, so 3800 watts on a 5500 watt generator should be no problem.  As for gas, that's out: I have it at the street, but I'd never recoup the costs associated with changing heating systems.  The question is still: what would be the best time to run the h20 heater?  At night, after using it, just leave it on because keeping it warm doesn't take as much energy as heating it up?
> 
> S



We are going to hook up to either a 2lb or 100lb propane tank. No need to hook up to city gas or listen to a generator run long enough to heat a tank of water.

Billy


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## vvvv (Oct 7, 2010)

http://electrical.about.com/od/heatingairconditioning/qt/electricwaterheaterelements.htm


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## Tarmsolo60 (Oct 7, 2010)

2 element tanks have only one element at a time operating, the top element always priority over the bottom element. This gives the user faster recovery for useable hot water when the tank is depleted of hot water.

3800 watt elements are for a 20 amp 240 volt circuit

4500 watt elements are for a 30 amp 240 volt circuit

If it were me, I would start the water heater an hour before I need it for showers, then let it run until the load is off the generator after the showers(you should be able to hear that on your generator). That would probably provide you with enough hot water until you start it again an hour before showers the next day.


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## vvvv (Oct 7, 2010)

Tarmsolo60 said:
			
		

> 2 element tanks have only one element at a time operating, the top element always priority over the bottom element. This gives the user faster recovery for useable hot water when the tank is depleted of hot water.
> 
> 3800 watt elements are for a 20 amp 240 volt circuit
> 
> ...


 so whats the swithing mechanism which tells top element to burn & not the bottom?


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## Tarmsolo60 (Oct 7, 2010)

The top thermostat must be satisfied temprature wise before it will transfer power to the bottom thermostat.


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## vvvv (Oct 7, 2010)

Tarmsolo60 said:
			
		

> The top thermostat must be satisfied temprature wise before it will transfer power to the bottom thermostat.


& so a "quick recovery" is better acheived by fewer watts from 1 element?


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## Tarmsolo60 (Oct 7, 2010)

a 2 element (quick recovery) tank will heat the top third of the water heater first to give the user access to hot water faster, then transfer the power to the lower element to heat the remainder of the tank.

If you have a 2 element or a single element tank and the thermostats  settings are equal then when both are done heating they will have used the same amount of energy. given the starting water temp, insulation are equal.

The only benefits to a two element tank is giving the user faster access to hot water when the tank is depleted of hot water. Or maybe some access to hot water when the lower elenet burns out.


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## vvvv (Oct 7, 2010)

Tarmsolo60 said:
			
		

> a 2 element (quick recovery) tank will heat the top third of the water heater first to give the user access to hot water faster, then transfer the power to the lower element to heat the remainder of the tank.
> 
> If you have a 2 element or a single element tank and the thermostats  settings are equal then when both are done heating they will have used the same amount of energy. given the starting water temp, insulation are equal.
> 
> The only benefits to a two element tank is giving the user faster access to hot water when the tank is depleted of hot water. Or maybe some access to hot water when the lower elenet burns out.


ignored this?& so a “quick recovery” is better acheived by fewer watts from 1 element? say so dont make it so! water heater will recover quicker from 2x the wattage, duh, u can reset the thermostats to whatever temp & they"ll react accordingly & INDEPENDENTLY...........your mechanical switching mechanism is yet to be revealed too


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## Tarmsolo60 (Oct 7, 2010)

Top thermostat only allows one element to heat at a time.
Qick recovery is better achieved by heating 1/3 of the water to usable temp first.Duh


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## vvvv (Oct 7, 2010)

Tarmsolo60 said:
			
		

> Top thermostat only allows one element to heat at a time.
> Qick recovery is better achieved by heating 1/3 of the water to usable temp first.Duh


thanx, new 2me. still, if both elements came on it would heat faster even with this setup, though it might trip the circuit breaker.


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## Highbeam (Oct 7, 2010)

Sure, if both elements fired simultaneously you would be providing more btus per hour and tank tamp would rise faster. However, you would overload the circuit. You could put ten elements in and really get hot water fast, instantly even. Heck, get rid of the tank and use an instant electric tankless water heater if you have that much power to spare.

If you know that only one element fires at a time, then your 5500 genset can heat the water. It doesn't matter when you run the genset but nobody likes to hear one all night. I would tend to heat the water right before use but would rather allow two hours for heat up if the tank is full of cold water. You'll hear a 3800 watt load turn on and off.


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## thinkxingu (Oct 7, 2010)

I actually hadn't thought about shutting the generator off at night, but I suppose there's no real reason to run it other than the fridge and lights if we need to get up.  Anything I'm missing?

S


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## Highbeam (Oct 7, 2010)

We always shut down at night. Nothing quite like the silence of a house with no power. Your gas 5500 watt genset will be consuming a LOT of gasoline when running whether it is loaded or not. No sense in running the genset and wasting that gas all night. Keep the fridge closed and do all your business before shutting off the genset and enjoying the evening watching the fire or sleeping soundly. Start it up in the morning to cool the fridge and to run the lights for your morning chores. You will have saved 8-10 hours of run time which is at least 5 gallons of gas, no ill effects. Honestly, I'll even shut down the genset in the middle of the day if there is no need for it. Conserving fuel can be extremely important if the outage might last more than a day. What if it was for a week and you only had 20 gallons of gasoline (not many have more than 5)? You'll want to ration your usage.

These things suck lots of fuel. Really, lots of fuel so don't just run the genset for fun.

Oh, and you'll need to look outside at your neighbors or check your own panel to see if the grid is back up.


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## thinkxingu (Oct 7, 2010)

Highbeam,
     Makes sense, thanks.  I think I'm gonna look into that device that indicates power has come back--there's a wire that wraps around the main in or something?

S


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## daveswoodhauler (Oct 7, 2010)

Same thing Highbeam said.
Run it during the day when needed, and shut down at night...don't wanna hear that thing purring at 3:00am 
During the Icestorm of Dec 2008 we lost power for 8 days....up here in NEw England thats tough....especially when you are on well water.


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## fbelec (Oct 12, 2010)

they do make fast recovery electric water heaters for commercial use. they are usually 120 gallon tanks with 3 upper elements and 3 lower. they are setup on a 70 amp circuit for single phase (residential) power or 30 amp 3 phase. they recover quick with 3 elements. stone cold 3800 watt elements heaters take a month of sundays to heat. 4500 watt which is standard wattage take 45 minutes to come up. commercial 3 element heaters take 15 to 20 to heat. and that's 120 gallons.


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## thinkxingu (Oct 20, 2010)

Interlock installed, outside outlet installed, water heater changed from second-meter-disconnect to main panel, inspection tomorrow.  Inspector said to just leave the H20 heater on when genny running--will not draw like a motor and the rest of the stuff I'll be running (fridge, couple lights, etc.) won't pull enough to tax the generator.  Finally, 'it takes more power to heat up a cool tank than it does to maintain a hot one.'

S


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## vvvv (Oct 20, 2010)

thinkxingu said:
			
		

> Interlock installed, outside outlet installed, water heater changed from second-meter-disconnect to main panel, inspection tomorrow.  Inspector said to just leave the H20 heater on when genny running--will not draw like a motor and the rest of the stuff I'll be running (fridge, couple lights, etc.) won't pull enough to tax the generator.  Finally, 'it takes more power to heat up a cool tank than it does to maintain a hot one.'
> 
> S


no way it takes more power to heat a cool tank than to maintain!.........whered u get that?


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## thinkxingu (Oct 20, 2010)

Maybe that was worded wrongly: 'Heating up a cold tank will draw the same power, 3,800 watts, but for a longer time than if the tank heat was maintained.'  Do you disagree with that?  I know it takes more overall power to heat up a cold house than to keep one warm.

S


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