Choosing right Power resistor for 100W and 40 Celsius degree ambient temperature

Patrick19 said:

,.yes, You are right.I want to use to heat air from a small box for chemical process done at 40 Celsius degree with thermostat( the easier task) .

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Well OK ... there's no need for a heat sink ... that 100W resistor is going to put out 100W anyway ....

It would be best to have a small computer fan (30mm x 30mm) blowing over the resistor , to make sure all the air in the box is well mixed and at the same temperature , otherwise the air will be hot at the top and cooler at the bottom ...

If for some reason you don't want a fan , lots of resisters running at reduced power would help even temperature throughout the box ....

Also a thermostat turning heat on and off will mean the temperature will go up and down between about 43 and 37, also be careful where you position thermostat ...

If room temperature is fairly constant you can by trail and error find out how much power you need to maintain 40C in the box , leave this power on all the time , and the temperature will not oscillate. ,, this must be the best choice.