I want to install a whole house fan but the only ones I can locate are ones that I must box in by cutting the rafters. Can I simply fasten the fan to the rafters above where I cut? This would create about a 6 inch increase in height above the opening but would this hurt? Any suggestions would be greatly appreciated!
If you don't put in some kind of frame under the fan (from joist to joist), you'll pull in a lot of attic air to recirculate.
Typically whole house fans are put into an existing hallway. If you know what you are doing you can use both walls as load bearing walls and cut the trusses. Then install cross supports from these cuts to the sissor parts of the trusses. A truss engineering company can tell you what new braces to use for a fee of couse. Whole house fans are best installed this way or like one of the other posts you can box above your truss system.