My old hot water is a Ruud px30-1. And its rusted at bottom and leaking. Need to replace. My problem im running into is i live in a mobike home my watts are 3500 and 240 volts. With 12 G wiring. My husband is disabled so i have to replace it. Can you tell me what type of hot water heater would be comparable so i wont have to change anything except the water heater. And inexpensive. Any advice is appreciated. Jb
Tanks, volts and watts
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Jadnashua
Retired Defense Industry Engineer xxx
You would need to supply how much room you have in the area where you want to install a new tank as the new ones tend to be a different size because they are required to have better insulation than the older ones. Given the 12g wire, you'd be limited to the 3500W. 12g is good for a maximum of 20A, but normally, you should not use more than 80% of that for something that might be on for a long time (say multiple showers, back-t0-back). Amps=Watts/volts, so 3500/240=15A, which is close to that 80% rule. If your voltage gets a little lower (not uncommon), the amps could go up some, which is one reason why the 80% rule is imposed on that type of thing.
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Thank you very much. I was told that i could go up to a 3800 without changing my wire as long as voltage was the same. But i dont think i can. You said my limit for the 12g is 3500?
Jadnashua
Retired Defense Industry Engineer xxx
80% of 20A is 16A...so, power=volts*amps or 240*16=3840...but, say your actual supply voltage was closer to 220vac, then 220*16=3520. As you can see, as your supply voltage drops (not uncommon during a brownout - it could go even lower), having a higher wattage unit could be putting you on the edge.
12g wire cannot have a bigger circuit breaker than 20A. Many water heaters have 4500W heating elements. You cannot use one of those unless you change the wiring and the breaker. The installation instructions will list the minimum size wiring and breaker, but a 3500W unit will work successfully (and to code) with your 20A supply circuit.
Now, your issue is what models will also fit in the available space. As I said, the new ones tend to be different because they are required to have more insulation.
12g wire cannot have a bigger circuit breaker than 20A. Many water heaters have 4500W heating elements. You cannot use one of those unless you change the wiring and the breaker. The installation instructions will list the minimum size wiring and breaker, but a 3500W unit will work successfully (and to code) with your 20A supply circuit.
Now, your issue is what models will also fit in the available space. As I said, the new ones tend to be different because they are required to have more insulation.
If i go with a 3800 w 240v with 12.2 g wiring will my 2 20 carry it or will i have to get a bigger amp
Jadnashua
Retired Defense Industry Engineer xxx
At capacity, without abiding by the 80% rule, a 20A circuit can provide 240*20=4800W. But, most of them (all?) require derating to 80%. 3800W would work IF your supply was really 240vac, but because it often isn't, 3500W is safer. You really need to read the installation instructions for one you might be considering. Otherwise, if your voltage was low one day, you'd end up tripping the breaker. That is most likely to happen during a hot spell when everyone has the a/c cranked up, and the main supply is being heavily loaded...the voltage tends to drop under those circumstances.
As the available wattage increases, on the same size tank, your first hour draw will increase. To get the same draw, you could go with a larger tank. The idea is that most people don't use max hot water constantly throughout the day, so even with a smaller wattage unit (if the tank volume is large enough), you will have enough time for it to recover by the next time you need a large quantity of hot water. If you're now running out of hot water, without changing the wiring, you need a larger tank while keeping the wattage the same. It will just take longer to reheat, just like the difference with boiling a 5qt pot verses an 8qt one.
As the available wattage increases, on the same size tank, your first hour draw will increase. To get the same draw, you could go with a larger tank. The idea is that most people don't use max hot water constantly throughout the day, so even with a smaller wattage unit (if the tank volume is large enough), you will have enough time for it to recover by the next time you need a large quantity of hot water. If you're now running out of hot water, without changing the wiring, you need a larger tank while keeping the wattage the same. It will just take longer to reheat, just like the difference with boiling a 5qt pot verses an 8qt one.
In wiring the gauge is lower number the higher the watts? Ok thank you . very much. Jb
Jadnashua
Retired Defense Industry Engineer xxx
While not exactly, one way to think about wire gauge is to think about how many could fit into say a 1/2" circle...so say you could fit 12 in, if the wires were bigger, you might only be able to fit 8 in...thus, 8g is a larger wire than 12g. In that same circle, you might be able to fit 28, and that would require the wire to be smaller, so 28g is a (much) smaller wire. Note, the size does not include the insulation, only the wire. The larger the wire (smaller the gauge), the more current it can carry. Power is the amount of current x the voltage (flow x pressure is another way to think of it).
