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keith6292 · Nov 7, 2009, 10:46 AM

I have 2 heaters connected to 1 thermostat, but it doesn't seem like there is much heat coming from the heaters... I have the power coming into the first heater then to the second and going to a single pole thermostat. Anyone have any ideas?

EPMiller · Nov 7, 2009, 09:24 PM

If you have wired them in series, yes, you will not get much heat. Only about 1/4 the amount. They must be wired parallel and then wire the thermostat to interrupt the one leg of the supply (or the HOT leg for 120v operation).

keith6292 · Nov 8, 2009, 07:33 AM

Originally Posted by EPMiller

If you have wired them in series, yes, you will not get much heat. Only about 1/4 the amount. They must be wired parallel and then wire the thermostat to interrupt the one leg of the supply (or the HOT leg for 120v operation).

So to do that I would first have to bring my power to the thermostat and then to the heaters?

ianmckinley · Nov 8, 2009, 11:05 AM

That would be the easiest way. Otherwise, you would need a 3-wire in between heaters.

keith6292 · Nov 8, 2009, 11:25 AM

Worked perfect... I have it connect in parallel with power to my thermostat. But what cause that to happen when you have it in series? Is it a voltage drop?

EPMiller · Nov 8, 2009, 07:03 PM

Watts / Volts = Amps
Volts / Amps = Resistance

For the sake of example let's say each heater uses 1000 watts of power at 240 volts (a common 4 ft strip). Using the first equation we get a current of about 4 amps through one heat strip. 1000W/240V = 4.17 amps When running 2 strips in parallel they each use 4.17A for a total of 8.33A.

Now plugging those numbers into the second equation we get a resistance of 57.6 ohms for each strip. 240V/4.17A = 57.6 ohms

When you wire them in series you would add the resistance of the elements (57.6*2 = 115.2 ohms), rearrange the second equation above and you get 240V / 115.2 ohms = 2.08 amps. Look back at the first paragraph and you will see that the current for ONE strip is double that amount of current. So in series you are getting one quarter of the heat of the same units in parallel.

See, they told you that algebra you were supposed to learn in high school would be valuable! :D

EPMiller

keith6292 · Nov 9, 2009, 04:42 AM

That is an awesome answer... I fully understand... and thanks for your help.

EPMiller · Nov 9, 2009, 07:37 PM

You're welcome.

EPM