Prissy is right. So are you.
It used to be done as you suggest with the old lamp bators, back before electricity was commonplace. These units used an oil-fired wick flame, much like the familiar kerosene lantern we know. This provided a heated air draft which was ducted into the egg chamber and regulated with a both wick control and proper venting.
Another way to "skin the cat," so to speak.
With a constant source of heat as you suggest, the way to control heat is by increasing/decreasing the heat source and using normal convection loss - heat escaping through the vents.
'Trouble is, this can be quite random without some careful calculation aforehand. It will take much experimentation and constant attention on your part to get he dimmer and vent losses working together. Thank goodness you dont have to also trim lamp wicks three time a day!
Most bators use a thermosat as a concession to convenience-thru-technology. An air mass, once stable and buffered in an insulated chamber, is near self regulating. Using low wattage heaters, forced air fans and thermostatic control of electrical current, we finally got what we needed for incubators - useful control with near adjust-and-forget convenience. We were "set," so to speak.
You can do it the way you suggest and for a low budget alternative it will work. I'd suggest, though, that you do your darndest to incorporate a thermo and fan. Good results will be more easily achieved.
I turn 40 this year, married, have kids ranging from 19-4 and definitely never have enough time or hands to get all the jobs done and done well!!
