I have a vacation home with LP gas. The home is two story, 1850 sq. ft. The Furnace is under the house. We have been told that the return Air Pipe and the Heat pipes servicing all of the rooms are to Small in Dia. I know that the return air is 20 inch. The Heat pipes I am not sure of the size.

What is the problem? Heating and cooling too slowly? Almost impossible to enlarge the wall piping without ripping out and widening the walls or chase on a 2 sty. Can you increase the airflow on the fan? Possibly raise the "off" limit switch temp? All of the supply side ductwork insulated in the crawl space?