wrote in message
...
I am finishing my basement. There was previously one duct to supply
the entire unfinished basement with air, which left it a little cool
in the winter. Now I'm creating a mechanical room of only about 150
sqft, a bathroom of 50 sqft, and a main room of about 700 sqft. I
have added two additional supply lines to heat the basement to a
comfortable temperature, and plan to install the requisite two
combustion air grates to "connect" the mechanical and main room. Do I
need to add a return air duct as well? Is it advisable or not for any
particular reason?


If you are planning to install a bath fan that will exhaust to the outside,
you should install a small duct to provide make up air from outside into the
furnace room. There have been issues with basement bath fans pulling flue
gases down the chimney and into the basement.