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Resitance Heaters?

jp_2 Member Posts: 1,935
proportional to T or temperature.

so R really isn't constant where things get real warm(hot).

R can go up or down due to T.


  • Larry_43
    Larry_43 Member Posts: 6
    Resityance Heaters

    I was wondering about resitance haeters. If you have an resitance heater that is rated at 208 volts and it is also rated at 240 volts and you are using the same heating element how can you increse your heat out put by increaing your voltage? isn't the heating element going to have the same resitance? for example if you have a 208volt haeter and a 2080 rester it will be 10 amps if you increase the voltage it will decreese your amps but will it put out more BTU's?

  • John Starcher_4
    John Starcher_4 Member Posts: 794

    .....Say it with me! Ohm's law, that is!!

    Volts = Amps X Resistance

    Resistance in the heater is constant, yes? Therefore, if voltage increases, then amperage must increase to "balance" the equation. Higher amperage and voltage = higher wattage (Watts = Volts X Amps), which translates to higher btu output.

    Hope this helps!

  • John Starcher_4
    John Starcher_4 Member Posts: 794

    ...did this help, Larry?
  • scrook_2
    scrook_2 Member Posts: 610
    E=I*R (volts=amps*ohms), also...

    P=E*I or Watts = Volts * Amps (at least for resistive loads, inductive loads like motors require you to also consider the power factor, but that does not matter here. Just don't ask me why E became voltage and I became current in electrical work)

    Since E=I*R (or I=E/R) and P = E*I, then, by substitution: P = E*E/R or: P=E^2/R, or: R=E^2/P

    Recall the heater' resistance, R, is fixed, so a 240V 1500W resistance baseboard has a resistance of (240^2)/1500 = 38.4 ohms. At 240V it will draw 240/38.4 = 6.25 amps.

    Use it at 208V and (208^2)/38.4 = 1,126.7 watts, and the current is 208volts/38.4ohms = 5.42 amps, or, another way: 1126.7watts/208volts = 5.42 amps.

    Notice the wattage drops faster (by the square of the voltage) than the voltage or current, e.g. half voltage (120V) would give 1/4 the wattage.

    The trick's to recall E=IR and (for resistive and DC loads) P=EI.

    Oh, by the way:
    1 kWh = 3413 BTU
    1 kW = 3413 BTU/hr
  • herb_4
    herb_4 Member Posts: 17

    i think he only wanted a simple answer. not a lesson in ohms law.
  • jp_2
    jp_2 Member Posts: 1,935

    whats that saying about givin a guy a fish or teaching him how to fish?
  • Ron Gillen
    Ron Gillen Member Posts: 124
    The rest of the saying is...

    In one case he has lunch . In the other, he sits in a boat all day drinking beer. Not always a bad thing.
  • scrook_2
    scrook_2 Member Posts: 610

    Or, appropriately(?):
    Build a man a fire and he is warm for a night, light a man on fire and he'll be warm for the rest of his life!

    Never stop learning!
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