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HI All: I am building a house. It is a 44’x32′ gambrel roof structure, with clear span gambrel scissor trusses. I have balloon framed the walls so that the scissor trusses sit on a 2′ kneewall upstairs. The “steep” pitch inside is 12/12, then bends to 5/12. The peak is some 14′ from the second floor…25′ from the first floor. The house is very open, with a 20’x16′ “open area” or “great room”. I have venting windows going into all 4 gable ends and 3 venting skylights.

The building is buttoned up, roof is on, etc. I need to run some wires, insulate, vapor barrier, then hang the ceiling sheetrock.

I would like to include a whole house fan so I can suck in cool evening air . My initial thought was to mount such a fan in the gable end below the ceiling, i.e. visible from the inside the house. Now that I have everything together, I’m thinking I’d much rather mount the fan in the gable end inside the scissor truss, venting to the outside through a shutter and pulling air from the inside through another shutter. I was thinking I would build a “duct box” around the fan to prevent air from being sucked from the attic (above the insulation, under the roof). This bottom of this “box” would be a shutter in the ceiling. I would also insulate this box. In the winter, I’d place some polystyrene or something in the box to prevent heat loss….then remove it for the cooling season. I have ample room to mount a 24″ fan…so I thought maybe I’d mount two fans on opposite ends of the gable end. The box “duct work” will be no smaller than the fan aperture (ie 24″) and slightly larger.

I have radiant heat, so there’s no ducting for air conditioning. Plus in the fingerlakes region of NY state, there’s usually only a handful of days that are very hot and humid. Air exchange in the cool evening will be plenty I suspect.

Any comments on installing the fans with this “duct work”?

Thanks much.