HVAC for 400 sq ft room size (roof, heating, insulated, convert)

[kwalk65]

We are building out our walk up attic to a bonus room - about 400 square feet. (We are a ranch built with attic space above the house) One contractor suggested HVAC to be a 1 or 1 1/2 ton unit. Another one is now suggesting that a unit like that would sound like a train coming through up there and is suggesting a heating/cooling wall unit.

Does anyone have any pros/cons or experience on using a wall unit?

Thank much!

[K'ledgeBldr]

This should be all you need for 400sq/ft-
Mitsubishi Electric - Mr. Slim Split-ductless

I used it on an apartment over garage project- perfect.
Needed power and thats it- no duct work, no line set, no separate condensor unit to make more outdoor noise.
And the unit itself is relatively quiet.

[kwalk65]

Thank you for your supportive and informative reply! I really do appreciate your time and expertise!

[johnsonkk]

There are way too many factors that are not listed. Where is this bonus room located? Is there 'knee walls' that will create a situation where the roof will be mere inches away? What kind of insulation will be in the walls or the space above this room?

The concern is not heating, it's going to be cooling. Had a converted attic with about the same square footage (400) and a 'house total' 3-Ton unit is barely workable in the dog days of summer. If you have no ductwork to the converted attic then you'll be stuck with a window-only unit.

[Barking Spider]

Obviously the room needs to be insulated properly.
400 square feet calls for less than 1 ton unless you are in Death Valley or Iraq.
I inspected a home recently that had the Slim unit, but it's winter, so I couldn't test the a/c.

1 1/2 ton units usually cost less than 1 ton units, but you really don't want to over-size it too much.