I have a high efficiency propane furnace which I installed myself about 3 years ago. I have a attached garage that is off of my kitchen witha open door way from kitchen to this room. This garage was finished off and is approximately 24 X 18 and is insulated very well. I have been using a vent free wall heater, but recently have removed this heater and was able to get through the concrete plate between the house wall and the concrete garage wall. I ran a 6 inch flex duct off my furnace plenum and installed a 2 X 14 register just below the step of this room. The thermostat is located in the living room and there seems to be about a 4 degree differance between the living room and this finished room which use to be the garage. I do not have a return in this room because it would be very difficult to install one at this time. I am looking to get more heat into thius room, should I increase the size of the flex duct and register to this room? If so what size? The register is located just off the kitchen just below the step about 4 feet off the floor. I shut off most of the dampers going to other registers in the house to try to get the furnace to run longer and heat up this spare room. I have about 8 6 inch runs coming off this furnace right now, furnace works great for the house without a problem. Please help.
