I am wanting to build a low powered resistor heater to heat a box about 10 cu/ft to 100 degrees and hold that temperature Constant. i will use a thermostat to regulate the heat. Here is my theory of operation. I wish to use a few 5w ceramic resistors in parallel/series using a 120v supply rectified ( either full or half bridge rectification). The idea is to build a long lasting power efficient heater for a egg incubator. My idea is to parallel and/or series as many resistors that it would take to hold the 100 degrees in the sealed enclosure. The questions that i have are first, how many resistors and what ohms could i use on a continuous basis and in what configuration. I don't need instant heat it can have warm up time. typically we turn on the incubator 2 or 3 hours before setting in the eggs. It will however have to be able to sustain the heat in the box at all times and from time to time the box must be opened to refill the water tray for humidity. So it will have to recover about 20 degrees in about 5 minutes max. There are two small lovers allowing fresh air into the box so that will have to be accounted for and there is a fan in the box that will circulate the air. I would probably set the resistors in front of the fan. The fan constantly runs. I was hoping to get away with 50 watts. however i can go higher if need be. But the lower the wattage to better the unit in my opinion. i like efficiency. Any help or suggestions would be most appreciated. Thanks!