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color me stupid somebody want to edumacate me?

Daddy Tanuki

Solar Wizard
Joined
May 11, 2021
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Flanks of Mount Fuji
so if I have two (2) 4500 watt 240 volt elements in series, then I get 120 volts across each, and roughly 1000 watts of heating from each? if so what would be the amps draw? sorry Ohms got my head messed up at the moment.

conversely, if I had two (2) 4500 240 volt elements in parallel then i get 240 volts across each and roughly 9000 watts of heating?

how does a normal US water heater wire the elements? i know they have separate thermostats but do they end up in parallel using 9000 watts, or do they end up in series using about 2000 watts?

the reason i ask is my soon to be dedicated to water heating inverter offers 5000 watts at 230 volts, its one of the euro type sigineer units. if one element is 4500 watts that maxes out the inverter with one element would it be better to use two and half (or quarter?) the heat output?

guessing it might be better to use just one.
 
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W = Vsquared/R

4500 = 240 squared/R then R = 57,600/4500

R = 12.8 ohms: when 2 are connected in series its 25.6 ohms.

120V = I x 25.6 so I = 120/25.6 = 4.69A
 
Heh, i was annoyed at the slow recovery times on a water heater, and in my youth I decided to tie both elements to the upper thermostat...

Yeah... bad things happened.

Ya know, i think the wiring in the heater is only #12, possibly thinner... it didnt like nearly 40A flowing through it...
 
If you halve the voltage, the power is reduced by a factor of 4.

Due to V^2/R, as @BentleyJ showed above.
So 4500W becomes 1125W

So if you rewired the elements in parallel, you could get 2250W at 120V.
But don’t ever change back to 240V!
 
ok so the consensus is one heating element per signeer 5000 watt inverter... might have to look for a fire sale and get another if I want this tank to heat up nice and hot in the winter.
 
It comes down to water usage, and how long you need to wait for the next person to take a shower after running out.
 
ok so the consensus is one heating element per signeer 5000 watt inverter... might have to look for a fire sale and get another if I want this tank to heat up nice and hot in the winter.
No...
Tank will happily switch between upper and lower elements with the 5000W inverter.
 
It comes down to water usage, and how long you need to wait for the next person to take a shower after running out.
Nope...

Only way to get faster recovery from a standard electric tank water heater is to install larger elements.
There is no safe way to energize both elements simultaneously.
 
so if I have two (2) 4500 watt 240 volt elements in series, then I get 120 volts across each, and roughly 1000 watts of heating from each? if so what would be the amps draw? sorry Ohms got my head messed up at the moment.

Roughly. 1/2 voltage, 1/4 power as Bentley said.
4500W/4 = 1125W.

Two in series fed 240V is 2250W, half what single element draws.
2250W/240V = 9.375A

conversely, if I had two (2) 4500 240 volt elements in parallel then i get 240 volts across each and roughly 9000 watts of heating?

Yes.

how does a normal US water heater wire the elements? i know they have separate thermostats but do they end up in parallel using 9000 watts, or do they end up in series using about 2000 watts?

Neither. As Supervstech said, it alternates one or the other 4500W. (until I rewire it.)

the reason i ask is my soon to be dedicated to water heating inverter offers 5000 watts at 230 volts, its one of the euro type sigineer units. if one element is 4500 watts that maxes out the inverter with one element would it be better to use two and half (or quarter?) the heat output?

guessing it might be better to use just one.

Many different wattages available, you can switch.

But avoid using a relay wires such that drawing an arc makes a dead short.
I have a 5000W + 5000W 240V duct heater, tried to wire series/parallel switchable for 10kW/2500W. When the relay switched it burned contacts and tripped a breaker. I rewired switching just one element for 10kW/5kW.

Nope...

Only way to get faster recovery from a standard electric tank water heater is to install larger elements.
There is no safe way to energize both elements simultaneously.

Two separate circuits, so wires not overloaded?
 
My 30 gallon tank sits at 155F all the time, and i installed a mixing valve to regulate hot water temp to the house.
Keeps the tank full, and slows the draw from the tank.

Perfect for large families on an electric water heater.
Two showers same time, zero cold shower issues.
 
ok so the consensus is one heating element per signeer 5000 watt inverter... might have to look for a fire sale and get another if I want this tank to heat up nice and hot in the winter.
The temperature will depend on the thermostat setting. Wattage determines how fast the water heats.

Winter or summer will be at the same max temperature unless the thermostat is adjusted.

If you need the higher capacity and have the power to drive two elements.... consider a second water heater in series. Heat pump style may save some juice.
 
When I had an electric heater a brand new one just filled with cold water was hot enough for a shower in 30 minutes.

Seemed fast enough for me.
 
I typed up a nice long explanation of pros and cons, had comedy intertwined and went to get the TC video to link in... and the browser lost my post... waaah...
Oh well, y'all can imagine what i wrote.
 
OK guess I should explain in a little more detail... this is a 1700 liter tank with insulation. I plan on heating my cabin with it and as over paneled as I am, I think i can run it strictly off of solar. Plan is too run a non pressurized system with two grundfos circulation pumps to move water into the two fan radiators that I got (cheap). Wall mounted individual thermostats turns on the circulation pump and the fan in the radiator for the two zones, so daytime with pletny of power all 800 square feet. at night only the bedroom (about 100 square feet.)

I will have a waste oil burner as backup for the coldest months to recharge the tank if solar is lacking, eventually I want to add some more panels on the west wall of my shed to lengthen out the solar day.

Basically when i hit 70 I do not want to have to cut firewood, and I am too cheap to buy kerosene. keep the woodstove for ambience but that's it... maybe a cord a year for pleasure only.


If you need the higher capacity and have the power to drive two elements.... consider a second water heater in series. Heat pump style may save some juice.
heat pump was first choice, but its too cold here in the winter. I can by top of the line japanese HPWH used 2-3 years old for about 1000 USD each (especially with the current yen to dollar rate). i was originally thinking of getting two to heat the tank, but investigations among the locals, and talking with some members here on the forum put the kibosh on that idea.

1st world problems, I know.
 
This should work very well If you have enough excess. How much excess can you reasonably expect?
 
Nope...

Only way to get faster recovery from a standard electric tank water heater is to install larger elements.
There is no safe way to energize both elements simultaneously.
There is another way. One can run a 2nd 30 amp circuit to your water heater like I did. I have two 5500 watt elements, each with thier own thermostat and 30 amp circuit.

*why did I do that?* because I needed 11kW of heating, 5.5 wouldn't do it.

Other than a few winter months I am net positive so I take a hefty credit into December. For years my radiant infloor system relied solely on a wood boiler but this oldish fart is getting tired of that so last winter I made some changes. I replaced my 18 year old water heater with a new one and ran a 2nd 30 amp circuit to it. "Two birds with one stone" Now I use up that credit before my COOP takes it at the 12 month true up and have nice warm floors without having to deal with the wood heat.

OK guess I should explain in a little more detail... this is a 1700 liter tank with insulation. I plan on heating my cabin with it and as over paneled as I am, I think i can run it strictly off of solar. Plan is too run a non pressurized system with two grundfos circulation pumps to move water into the two fan radiators that I got (cheap). Wall mounted individual thermostats turns on the circulation pump and the fan in the radiator for the two zones, so daytime with pletny of power all 800 square feet. at night only the bedroom (about 100 square feet.)
See my response above.

I will mention that those Grundfos "pumps" aren't pumps. They are circulators that are not designed to work in a non-pressurized system, trust me, I've fought it for years on my personal system. Anything less than 12PSI on the suction side and they are very likely to cavitate and loose prime.
 
heat pump was first choice, but its too cold here in the winter. I can by top of the line japanese HPWH used 2-3 years old for about 1000 USD each (especially with the current yen to dollar rate). i was originally thinking of getting two to heat the tank, but investigations among the locals, and talking with some members here on the forum put the kibosh on that idea.

1st world problems, I know.
Ultimately if the heating element is 4500 watts that is all the energy there is to heat the entire place. Or about 15k BTU. Is that enough?

I get the heat pump issues as it still needs to pump the heat out of the structure if space heating.
 
This should work very well If you have enough excess. How much excess can you reasonably expect?
with current panels in the winter, about 25 kw after batteries are at float. which by my calculations is not enough. hence i want to add some west facing panels on my shop, another 2 or 3 kw of panels vertical facing west to give me a few more hours.

With my new banks added in I have a 70kWh bank of which I rarely use more than about 10-12kWh through an entire 24 hour period so I can even draw some from my bank, but that will be a net loss as I have to replenish it the following day.

lastly I will have a waste oil burner attached to the tank for the coldest months. How much energy will it produce I am unsure of as of yet, as I am still making it. but when running the unit dry with no water, it was enough to make the 1/2" thick walls of the Co2 cylinder i used to make the main chamber glow red hot so it takes a few BTU's to do that. this is all one huge time consuming experiment to keep me busy on my off hours. if it does not work initially I will add as many elements and panels as needed until it does.
 
There is another way. One can run a 2nd 30 amp circuit to your water heater like I did. I have two 5500 watt elements, each with thier own thermostat and 30 amp circuit.

*why did I do that?* because I needed 11kW of heating, 5.5 wouldn't do it.

Other than a few winter months I am net positive so I take a hefty credit into December. For years my radiant infloor system relied solely on a wood boiler but this oldish fart is getting tired of that so last winter I made some changes. I replaced my 18 year old water heater with a new one and ran a 2nd 30 amp circuit to it. "Two birds with one stone" Now I use up that credit before my COOP takes it at the 12 month true up and have nice warm floors without having to deal with the wood heat.


See my response above.

I will mention that those Grundfos "pumps" aren't pumps. They are circulators that are not designed to work in a non-pressurized system, trust me, I've fought it for years on my personal system. Anything less than 12PSI on the suction side and they are very likely to cavitate and loose prime.
wonder what the pressure is from a 2 meter elevation change? my property is on a a slope and this thing is going to the back of the house on the slope so it will be at least 2 meters higher than the circulators... wonder if that will be enough, or if I will have to spring for something more robust.
 
Ultimately if the heating element is 4500 watts that is all the energy there is to heat the entire place. Or about 15k BTU. Is that enough?

I get the heat pump issues as it still needs to pump the heat out of the structure if space heating.
good question. I currently have no way of measuring that as I burn wood in a fairly inefficient woodstove, and it bakes us out if we do not throttle it all the way down.

thats one of the reasons I was thinking about adding more elements, rather have overkill then not enough. the house is now well insulated and sealed where it was not before (new siding, under cladding and some real insulation. along with tyveck, and caulked seams for all the under cladding.
 

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