I am getting to the point of deciding what type of heat to install in a new
workshop. The shop is 30'x54' with 10' walls and will be insulated to R-20
in the walls and R-38 in the ceiling. I have natural gas available and am
trying to decide between using one or two of the ventless "blue flame" gas
units or a single ceiling mounted vented gas furnace. The ventless units
would be less expensive and have a few other advantages, but I have heard
that because they do not vent combustion air outside of the building they
can lead to potential moisture problems. Is this an issues to be concerned
about? The shop will be used for woodworking and fossil/mineral preparation
so a moisture problem would not be good.

Thanks for any recommendations or advice any one has.