I've heard of some people use light bulbs (the tungsten type), but I'm not sure how much heat it would emit, though 80% of the wattage is heat (infra-reds). So a 100w bulb emits 80w of heat, you may try to transfer that to BTUs to compare to heaters and such.
MOD EDIT: Sig only takes up 6 lines now. Fermenting: Apple cider x 2, Doppelbock, Red, Oatmeal Stout, West Coast IPA x 2
Bottle conditioning: RIS
Keg conditioning: La Fin du Monde clone
On tap: Maudite clone, Double Munchen, Oktoberfeast, Oktoberfest Pilsner
Planning: Brewed in 2011: 22 (2010: 15, 2009: 29, 2008: 21, 2007: 1)
Wine made in 2010: 6 kits (2009: 19, 2008: 30)