Thanks. The key was that you have venting up there. Yes, the heat from your heater in winter should get reflected back down. 'They say' that the savings can be as much as 10% but usually ranges from 2 to 3%. Heck, that could be significant for you where the 'system' pays for itself in a few years.
Good luck to you w/all that. Your 'system' is a sound one IMO.