Water heater design
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Posted by: automan3042 ® 04/04/2007, 19:11:23 Author Profile eMail author Edit

How does one determine the power rating of a heating element for a water heater and which voltage would be better suited, a 110V or 220V supply?

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Re: Water heater design
Re: Water heater design -- automan3042	Post Reply	Top of thread	Forum

Posted by: Bruiser ® 04/04/2007, 22:17:41 Author Profile eMail author Edit

You need to work out how quickly you want how much water heated from inlet to outlet temperature. Q = mc x(t2-t1). For water this is 1Joule per litre per degree. P = Q/s. (s = time in seconds) If you have insulated storage, you can do this quite slowly. If you want something instantaneous then obviously the power rating will be higher. With regard to voltage, it goes back to a variation on Ohm's law, P = V^2/R. Either will work, but if you double the voltage you get 4 times the power into a given resistance. Finally, don't forget a thermostat to control the whole thing. If you picture the thermostat cycling on and off periodically, you'll see that the precise value of the element resistance is not critical as long as it's not too small.

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Re: Re: Water heater design
Re: Re: Water heater design -- Bruiser	Post Reply	Top of thread	Forum

Posted by: mikeweber3 ® 04/09/2007, 13:01:43 Author Profile eMail author Edit

Most heating elements are rated at a specific wattage for a design voltage. If your heater is not labled, please measure it, describe it, and give us the ohms resistance.

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