Symptoms
- New microwave is too large, small, or a different shape than the old one
- Trim kit or cabinet cutout doesn't match the new unit
- Vent opening on an over-the-range model doesn't align with existing ductwork
- Mounting bracket or template differs from the old installation
Likely causes
- CommonDifferent exterior dimensions between brands or modelsEven similar-capacity microwaves can vary in width, height, and depth between manufacturers.
- CommonMismatched trim kit for built-in installationsBuilt-in microwaves often need a specific trim kit sized to both the unit and the cabinet opening.
- PossibleDifferent venting configuration for over-the-range modelsDuct size, direction, or recirculating-vs-vented setup can differ between old and new units.
What to do
- Before purchasing, measure your existing cabinet opening's width, height, and depth precisely.
- Compare those measurements against the new microwave's specification sheet, not just its general size category.
- For built-in installations, confirm whether a specific trim kit is needed and that it matches both the new unit and your cabinet opening.
- For over-the-range models, check that the new unit's vent size and direction (up through the cabinet vs. out the back) matches your existing ductwork.
- If there's a mismatch, look into an adapter trim kit or duct transition piece before assuming the cabinet itself needs modification.
- For anything requiring cabinet modification or duct rerouting, consult a kitchen installer or contractor rather than forcing an ill-fitting installation.
Tools and parts
- Tape measure
Microwave trim kitSearch: “microwave built-in trim kit”
Range hood duct transitionSearch: “range hood duct transition adapter”
When to call a pro
If the new unit needs cabinet modification or a different duct configuration, a kitchen installer or contractor can assess and complete the fit properly.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.