The question is whether (1) cooking rice in a pot of boiling water for an hour and then leaving the pot (of water and rice) to cool to room temp heats my house the same amount as compared to (2) just boiling a pot of water for an hour and leaving it to cool as compared to (3) simply leaving the stove flame on for an hour. Assume an identical stove setting for all three scenarios of course.
My inclination is that when cooking rice, much of the energy is absorbed by changes to the bond structures of the rice (just as a sweet potato converts to simpler sugars when cooking) and this energy will not be radiated back when you allow it to cool, and thus it will heat house less than (2) or (3).
As for (2) versus (3), my inclination is to say that if all of the water vapor that boils off stays in the house to condense, the two scenarios will heat the house identically.
Best Answer
I Googled in vain for the enthalphy change in the hydrolysis of starch to disaccharides, however a quick survey of dieting web sites suggests both starch and sugar have about the same number of calories (360-380 calories per 100g depending on what web site you believe). This suggests that the enthalpy of hydrolysis of starch to disaccharides is small, or at least small compared to the heat losses from a pot of boiling water.
In your three experiments you're putting in the same amount of energy i.e. burning the same amount of gas. If there is negligable energy taken up hydrolysing starch, and if nothing escapes from your house, then all three experiments will end up heating your house by the same amount.