We are going to replace our two 19 year old 1 stage Heil gas furnaces. We live in Charlotte, NC so we don't have extremely cold winters. Our first furnace is in our crawl space and heats our 2400 sq ft first floor, and our second furnace is in the attic and heats our 1800 sq ft second floor.
We have had heat equalization issues both upstairs and downstairs with our 1 stage furnaces. Our downstairs thermostat is in the front entry hallway. We often need to close the doors that let air circulate between the front and back areas of our first floor. As a result the back of the first floor where we spend most of our time tends to get less heat than does the front. It's especially cold in our family room which is the furthest distance from the furnace. We have thought about adding a new zone to the back of the first floor so that we can better control the heat going to this area, but we have been told that this solution is expensive and not necessary. We have been told that a better solution is to replace the 1 stage gas furnace with either a Trane XL 90 regular 2 stage gas furnace or a Trane XV 90 2 stage variable speed gas furnace. Will either or both of these 2 stage furnaces let us equalize the heat between the front and the back of the first floor? Will the 2 stage variable speed furnace do a significantly better job of equalizing the heat than the regular 2 stage furnace? We know that the 2 stage variable speed furnace is more expensive, but our contractor is willing to include a whole house humidifier with the variable speed furnace at no extra cost while we will have to pay extra for the humidifier if we choose the regular 2 stage furnace.
On our second floor, the master bedroom has more ducts than do the other three bedrooms. The thermostat is in the hallway and when all of the bedroom doors are shut, the master bedroom gets uncomfortably warm before the other bedrooms become comfortable. Again we have been told that a regular 2 stage or a 2 stage variable furnace will help solve this problem. We have also been told that we may only need an 80% AFUE furnace upstairs instead of the 90% AFUE furnace that is recommended for the first floor. Is the 80% AFUE furnace OK for upstairs? Again will the 2 stage variable speed furnace do a significantly better job of equalizing the heat than the regular 2 stage furnace? The whole house humidifier is only included on the first floor furnace so we will get no price break if we put a 2 stage variable speed furnace upstairs.