My $ .02 is that the sunroom is pulling a large amount of heat away from your living space, espeically if it has a northern exposure. Those bricks will suck a ton of warmth out of your living area at night, and the windows (especially if they are single glazed) will have significant thermal transfer as well. If the sunroom has southern exposure, use it to your advantage and leave the window shades up during the day to "load" the thermal mass of the brick floor for nightime radiation. You can cover those windows with heavy drapes to good advantage also. If you do, make sure the drapes either have a cornice on top, or that they "puddle" at the bottom to prevent a chimney effect that will pull cold air up to the top of the windows. Aside from those obvious things, you'd probably do well to check for air leakages. Do you have heating vents in the ceiling? If so, pull a register cover and see if the duct work fits snugly to the sheetrock cut on all sides. (I recently found out all of mine had significant gaps, allowing cooled and heated air to just blow back up into my attic space) A can of spray foam can be blasted in those gaps, trimmed flush with a knife after it cures. If you are not going to use your central air at all, look into making some plywood and foam covers, which you can mount to the outside of the ceiling register using rare earth magnets. Those uncovered vents can create a good path for warmed air to wander up out of your living space. How about weather stripping on all exterior doors? Take a close look especially at the bottom. Their should be no daylight over the threshold. Foam gaskets to cover air leaks in switch and plug outlets along exterior walls is an easy and cheap thing to do. It makes a bigger difference than you might think. If you have large interior temp differentials, use a floor fan to push the colder air towards the stove, which will set up a convection loop. The result can be pretty dramatic. Do you have any other ceiling penetrations, such as recessed fixtures or pendant lights? You can seal the trim of your recessed fixtures with caulk from the interior side. Spray foam over holes in junction boxes can be done on attic side. Look for pass-throughs in the ceiling for things like kitchen fan ducts, plumbing chases, etc. Be careful about putting insulation up and over your recessed fixtures though....they need to be rated for that. Remember too: Fiber insulation is not an air barrier, it is only an air filter. Where you see dirty insulation, your pulling or pushing air through it. No doubt: verify that you have a block-off plate in place. Trying to heat the universe is a weary and lonely undertaking. Getting your house to a better level of energy independence...and that does sound like your goal... doesn't just end with getting the stove installed, and burning good wood. It is an ongoing job of incremental improvements. Over time, they will really begin to make a difference.