A slightly radical solution follows. This assumes your furnace, or your ducts to your bedrooms, are in the attic.
parts:
Fantech 12″ duct fan
12-12-12 wye
12″ motorized (zone) damper
12″ insulated flexible duct
Wall thermostat
Fan control relay
25′ extension cord; cut off female end.
thermostat wire as needed
Duct tape
Splice the wye into the 12″ air duct coming from the furnace and before the rooms.
Connect the duct fan to the wye using flexible duct.
Suspend the duct fan so it is not resting on ceiling joists.
Connect the damper to the fan using flexible duct.
Mount the damper so the outlet is free and not pointing at any blown-in insulation.
Wire the fan control relay to the fan and the 24v from the thermostat to the motorized damper.
Wire the extension cord to the fan control relay.
Plug the extension cord in the attic outlet.
Run thermostat wire down to wall location in primary bedroom.
Install thermostat on wall location in primary bedroom.
The result is a “whole house” fan that automatically switches on to exhaust room air up and out through the existing air ducts. It is quiet, not because the fan is quiet, but because it is insulated by the fiberglass surrounding the ducts. It uses the existing ceiling penetrations, so no new holes have to be cut.
It is powerful enough to generate a healthy breeze through an open window.
You can scale down the project to a 10″ or 8″ fan. Evaluate the CFM ratings of the fans to judge whether these smaller solutions will work for you.
The Fantech duct fans are robust, and can be speed controlled using an ordinary wall dimmer. So if the 12″ duct fan is more powerful than necessary, and is noisier than desired, you can reduce the speed (and noise) to suit.
The one downside to this approach is the fan sucks dusty room air inside the ventilation ducts, and some of the room air dust collects inside the ducts. However, I haven’t found this to be much of an issue. Perhaps the reason is the registers are located up high in the room so the dust settles out before being sucked up the duct.
Like any “whole house” fan, it requires that your attic be sufficiently ventilated to let the house air out. I haven’t yet encountered an attic that wasn’t.
