In order to use any type of cooktop safely, you will need to have adequate air circulation around all sides of the cooktop and below it. Follow these directions to expand the cut-out in your existing countertop so you can install a new cooktop in a way that will prevent dangerous heat build-up that may cause a kitchen fire.
Step 1 - Inspect and Adjust Supporting Structure of the Countertop
If the countertop surface was installed over a solid counter backing, you must create a floating support for air circulation under the cooktop. Remove the countertop finish from the backing. Cut away the wood or fiberboard from the lower cabinet top. Cut plywood strips the same length as the depth from front to back of the cabinet edges below. Install these three inches apart from the outside edge to 1-1/8 inch away from either side of the expanded cutout size. If the countertop is already on a floating framework like this, proceed to step two.
Step 2 - Measure the Expansion Size Needed
Measure the new cooktop size and add 1/8 inch to each side in width and depth. Measure the existing cut-out to determine how much larger you need to make it.
Step 3 - Enlarge the Cut-Out for the Cooktop
Cut through the marble granite, or a tile countertop with a specialized rotary cutter, fitted with a bit suited to the material. Use the power sander to smooth and slightly round off all the interior edges of the cut-out. Curve the sharp interior corners by about two degrees with the power router, to prevent heat from cracking the countertop. Sand all surfaces once more before inserting the cooktop using 150-grit sandpaper on the power sander for optimum smoothness. Bevel each of the reinforcing blocks at 45 degrees on the two edges where the cut-out corners will bear weight. Place one reinforcing block under each corner of the cut-out and secure them with a smooth layer of joint adhesive.
Step 4 - Insert and Secure the Cooktop
Affix aluminum heat-conducting tape around all the vertical edges of the cut-out, and allow it to hang downward. Put a wide strip of this tape on the horizontal top edge of the cut-out so it will show when the cooktop is dropped in. Set the cooktop into the counter cutout so it is centered. Check with the carpenter's level to ensure it is flush and straight with the countertop. Fasten the cooktop in place with the power drill and screws, inserting a thin wood slat between the pointed screw end and the granite, marble, or tile counter material. Score off the excess aluminum tape at the top and bottom, and your installation is done.