Before you begin this project, the circuit that the existing range hood should be identified and the power to that turned off. This can be done without any special equipment. Turn the light or the fan on and simply turn off the breakers one at a time in your circuit breaker panel until the light goes out or the fan stops running. If neither the fan nor the light is functioning then you will need a circuit tester (available in any hardware or electrical supply store).
Double check the dimensions on the new range hood to assure proper fit.
Check the installation manual for the proper clearance from stovetop to range hood.
Place a piece of plywood over the stovetop to protect it and provide a work surface. If you do not have a piece of plywood, use the cardboard box from the new range hood.
Locate the power junction box on the underside of the hood. This is usually a small metal box held on with a sheet metal screw. If it is not visible, then you will have to remove the filter cover and filter to expose this junction box. The cover will snap off easily and the filter slides out. Remove the screw and cover and release the electrical connection inside. There is also a wire tensioner affixed to the box. Loosen the 2(two) screws on the collar of the tensioner. It is not necessary to remove the wire tensioner just loosen the screws enough to let the wire slip through the collar.
The range hood can be removed by releasing the attaching screws located on the underside of the hood. There are usually 4 (four) screws but each installation is different. Remove all screws except 2(two). Leave an inside and an outside corner attached. These last screws will support the fixture while you position your hand under the hood for support or have a helper support the hood. Once your hand or the helper has a firm hold on the hood remove the last 2 (two) screws and lower the unit down until you can guide it clear of the area.
If your range hood is vented outside, there will be a duct adapter attached to the back. This should just slide away from the duct. A new adapter should be included with your range hood.
The new hood has a āknock-outā plate in the rear of the unit. Remove this to allow the electrical wire to pass through.
Install a new wire tensioner through the āknock-outā hole. However, (here is the ātrickā) install it backwards or the range hood will not fit flush against the wall.
If the range hood does not have pre-drilled mounting holes, it would be a good idea to drill them now (one in each corner will do).
If the new range hood has an outside duct, then attach the duct adapter to the rear of the range hood after removing the cover plate.
Slide the wire through the tensioner but do not tighten at this time.
Position the new range hood in the opening while sliding the duct adapter (already attached to the back of the range hood) into the exhaust duct.
While supporting the range hood, attach one inside and one outside corner. Do not tighten the screws completely at this time.
Make final adjustments in position assuring that the mounting ledge is flush with the supporting cabinetry.
Place the last two screws, tightening firmly.
Tighten the remaining screws
Connect the power cable from the range hood to the house power line with wire nuts.