Range Hood Vent

Question

Where can I find info on installing a rectangular range hood vent?

Answer

The standard size vent duct for a range hood is 3 1/4" x 10" or 7" diameter.

You can purchase the duct and transition pieces, angles, etc. at most building supply stores.

You'll find that the 3 1/4x10 duct has a wall and roof cap that are compatible to it. The duct should be insulated in the attic to prevent condensation. Try to keep the duct as short as possible with as least number of 90 degree turns as possible. Each fan has a rating which allows so many feet of duct to the outside, 90 degree turns use up a certain amount of this allowable footage.

The duct comes in a flat piece which is cut to length before assembling. Screw the joints to prevent separation with 1/2" x #6 pan head sheet metal screws and tape the joints with silver duct tape not the regular duct tape. The wall cap is used on an exterior wall where the duct discharges. The roof cap is used on the roof. You use one or the other.

Run the duct through the wall and down the cabinet. The duct should extend down through the cabinet by about 1/2", then cut the corners and fold the sides and ends back against the bottom of the cabinet.

The range hood should have a lip which is screwed in place which extends up about 5/8 to 3/4 into the duct under the cabinet. The hood is then screwed in place to hold it secure.

The 14/2 wire with ground comes through the wall, no electrical box, into the hood knock out hole. Use a box connector to protect the wire. Make a hole in the drywall large enough to make room for the connector. Connect the wires from inside the unit accessible from under the hood.

All you should worry about for now is getting the duct in and coming through the drywall where the cabinet will go. Then you can put the drywall in and after the cabinet is in you can carry on with the 90° elbow and cut the cabinet bottom for the duct to pass through. The wire is no problem, just estimate where the hood will be, aim high rather than low. Leave the wire sticking out of the drywall at this point. You can always cut the drywall later and move the wire, if you are close.

The wire usually is 3/4" down on the right side of the hood and about 7 1/2" offset from center, as viewed facing the installed hood. The top of the cabinets in an 8' ceiling are at 7' leaving 1' for airspace. The cabinet over the range is set 24" above the range to the bottom of the hood. The hood is 6" high, leaving the cabinet 18" high.

Dave