I am new here and am involved in a major home renovation in South Carolina. All the floor joists and sill beams will be replaced. There is a dirt crawl space with approximately 6 inches of loose sandy clay before hitting heavy clay. Is it possible to feed the stove outside the home and have the mass under the home in the crawl space? House is 48 feet long and 33 feet wide. If the crawl space is sealed and insulated, wouldn't that be a good place for the mass?
My first reaction is - having the feed tube outside the house sounds incredibly inconvenient.
If the mass is located under the house, how do you expect the heat to permeate into the habitable space inside the house? If there's an airgap between the mass and the floor, I imagine it would take an eternity to heat the house.
If you are rebuilding the floor, then no better time to beef up the for the weight of a mass inside your home. Your idea of an under floor mass fed from outside is just not practical. The Romans successfully used a floor heating system ... worked great ... unfortunately several slaves were tasked with feeding that fire all night long... A RMH is best situated in the room everybody spends time in. It is easy to feed and the mass is right there to snuggle up to. A RMH located elsewhere is a chore... will not be tended properly , will produce more ash than normal and generally will lead to disillusionment with the whole idea ! Make your RMH part of your home ... treat it like a family member with caring and attention and you will LOVE your RMH and it will love you back, with drastically reduced wood consumption, a tiny carbonfootprint compared to a regular wood stove. Oh and never a chance of a chimney fire EVER!
I would add that there is one situation where an underfloor mass could work: If the mass is the floor and not beneath a wood-framed floor.
You could either build the fire core into a recess in the floor, like a little sitting alcove, and run the mass from there, or if you have good draft in a tall chimney, you may be able to drop the flue below floor level from a standard core layout. You would need to have the floor surface be some sort of masonry - tile, brick, stone, earth... You would also need to insulate well beneath the mass so it isn't trying to heat the whole earth below the house.