I have a Rheem Chriterian furnace and I have a semi large house and my duct work is not insulated. I have a partial basement where my furnace is located. Problem is that when the heater is on and the flames are blowing into the furnace it heats great but the flames go out and the blower continues to blow for a couple, maybe three minutes, and the last minute or so it blows cold air. You can tell that it has a huge effect because it will get real warm and then it cools itself right back off in the house. Is there any way of adjusting the amount of time the blower blows after the flames shut off or do I just need to wrap all of my duct work to try and maintain the heat? I would like to do that anyway but it will be costly right now and we all know how tight money is these days. I would just like to be able to keep my furnace from blowing out that cold air at the end of its cycle for now.

Look in you owners manual. There may be some very small switches on the furnace control board that will adjust how long your blower stays on after call for heat is ended. If you don't have the manual, just look in your furnace and tell me if you see any very small switches on the board. How old is your furnace? Is it spark ignition or glow plug?