This is a big change coming in residential & light-commercial furnaces. Effective June 1, 2013, federal law requires that minimum furnace efficiency in the Northwest must be 90%. That means that 80 percent furnaces cannot be installed after that date.
All things being equal, many people would opt to pay the upcharge for a 90 percent furnace anyway. But there are some jobs where it is not feasible to retrofit a 90% furnace. For example, if you have a situation where a chimney is venting for an 80 percent furnace and a gas water heater, and there is no path to run a new PVC vent for the 90 percent furnace, that is going to be a problem.
You can’t vent the 90 percent furnace in the chimney with the water heater, and if you dedicate the chimney as a path for the 90 percent furnace vent, the chimney can no longer be used to vent the water heater. This is a dilemma that could be very difficult and/or expensive to solve. Unfortunately, there are no exceptions in the code for such difficulty. All I can say is that it will take some creative minds to solve this problem.
At Air Control, we feel we can do anything, but this will add to the cost.