I'd like to use a ceramic heating resistor to keep a 4-5 cu ft insulated box above freezing on cold nights. A 15w heater belt is too much so I was thinking about using either a 5w or 10w heating resistor. Seemed like something I could eventually design a circuit to control the heat with a DS18B20 sensor and an Arduino.
Does the following look correct or am I missing something?
The resistor I looked at, a Riedon UAL-5, is rated for 1500 VAC. I assume I can run it at 120 VAC which is the RMS value for house AC. I=P/V so 5w/120v = 0.0417 amps. R = V/I so 120v/.04a = 3000 ohms and that would be the size of the resistor I need to generate 5w?
Does the current need to be rectified?
PDF of a part I was considering which will mount nicely on a heat sink:
EDIT1: I've done some empirical tests with a 15w heater belt that I borrowed off of a friend and I know the insulation is good enough that 5-10w will be enough. It's the calculation for the resistor and question on rectifying that I was sure of. Not to mention that I can always move up in resistor wattage.
I appreciate the answers about area heating and insulation but I purposely didn't ask about that. I guess I should have said ignore the insulation and area heating as I can deal with that. What I really wanted was to understand the calculation and then I would buy the size of resistor I thought was appropriate. Now that I think about it I'll probably go 10 or 2x5 on separate switches.
I was going to use a grounded electrical box ventilation hold to contain the resistor and heatsink along with shrink tubing on the connections. I am aware of the cautions around using 120v.
I appreciate all the answers. Thanks Barleyman. Barley?