Gas and Oil Home Heating Furnaces - Heat duct, quantity and size?

We have added a "great room" to our existing home. The room is 22' x 32' with a cathederal ceiling which is 13' up at the peak. The ceiling is insulated with R-38 insulation. The outside walls are 6" (R-19). There are no inside "framed" walls in this room so it's just a big open space. There are several large patio doors and windows facing south which provide good heat during daylight hours.

There is a well insulated crawl space (cement floor) under the room. The foundation is a 8" poured wall with 3" foam insulation forms (insulated inside and outside the concrete)

Although there IS a gas fireplace in the room, I want to insure there is adequate furnace heat to keep the room warm when not using the fireplace.

It is now time to run the heating/cooling (central air) ducting.

How many 6" ducts should be needed to heat this area?

We have a Lennox "Pulsar 2" furnace with central air which, when installed, was sized to provide the amount of heat and cooling needed for the room

the only way to know for sure is to perform a heat load on the room. go to hvac-talk.com . there is one available there