Wall Oven Height Gap
When the new oven fits in its place width-wise but leaves a gap at the top, this gap can be closed off, or if it is large enough, converted into extra storage space in the kitchen. This type of fix is the simplest of scenarios to address because you only have to address the space above the oven and not on the sides. Measure the width and length of the face of the opening above the self-cleaning wall oven, as well as the depth. Have a custom cabinet constructed to fit in the space, if it is large enough for one. To simply close the opening in, cut a piece of wood -- either plywood or solid 1-inch wood board -- to fit the face of the opening. Use 2-by-4s cut to the depth and width measurements of the opening and screw them together and to the sides of the gap, to form the frame of the opening. Position the frame about 1 inch recessed from the front so that the face piece will rest flush with the front of the existing oven cabinet. Screw the face piece of wood into the frame, and stain or paint it to match the cabinet.
Wall Oven Width Gap
Fill in the gap on the side, or sides, of the wall oven with wood trim cut to the width and length of the gap, if the gap is small. If the gap is substantial, frame the opening with 2-by-2s or 2-by-4s, cut to fill in the space, and bring this frame within 1 inch back from the front of the oven cabinet. Use 1-inch-thick wood boards to cut a piece to the exact width and length measurements of the face of the opening. Nail it into the frame, and stain or paint it to match the rest of the cabinetry.
Floor Oven
When a free-standing self-cleaning oven and stove unit does not fit into its opening, this can also be corrected with a frame on one or both sides of the unit. Use the width, length and depth measurements to construct a rectangular frame from wood boards that will slide on the side or sides of the oven. These fillers will close in the gap with a frame whose front is flush with the cabinets and oven. Paint or stain the filler or fillers to match the cabinetry.
Decor Ideas
Instead of just staining or painting the wood that frames and fills in the gaps around an oven smaller than its space, use this as an opportunity to add a decorative feature to the kitchen. Use glass or stainless steel tiles normally used for a backsplash to frame or flank both sides of the oven as a covering for the gap filler. These tiles can match or coordinate with the kitchen's backsplash or countertops, a neat solution to the oven's problem and a stylish update to the kitchen's decor.