I would appreciate anyone's comments on my overall plan. I have a 1950s three level house with a rearaddition from 1964. Heating came from a gas forced air furnace in the basement. The ductwork was added-on to the addition and never worked properly. Now I am adding yet another addition., so this is a real hybrid house. I want to take down the existing ducts and install a bigger unit in the attic and install ducts that go down to the main floor rather than up from the basement. Where can I find a duct designer? Can one hire a separate hvac inspector to be sure it is done right before closein?

The basement I am making into a semi-separate, 3 room unit with its own heating. It does not need cooling, although it could use air flow to take out the humidity. What would you suggest for heating this 400 sq. ft. space with a 200 sq. ft. room on the side that was formerly the underground garage? I have gas and electric there, but was thinking of just a good quality baseboard unit. I am thinking of putting in a ventless fireplace in addition to regular heat both upstairs and in the basement, because they give off a lot of heat in case the system is overwhelmed on very cold nights.