Forum participant Panama stated on another post:

"Manual S has a graph in Appendix 4 that shows negligible loss in efficiency if a modern furnace (AFUE > 75%) is oversized up to 5 times the heating load"

Participant beenthere stated he did not believe the statement was reliable (or words to that effect).

I'm faced with having to use a much larger than necessary furnace to handle the air on a 5 ton AC unit. If the above reference is true then I would feel better about having to oversize the furnace (on the other hand it really doesn't matter how I feel about it!)

What are the opinions about the above Manual S reference given the professional participants' experience?