What you need to do before you start
Replacing an over-the-range microwave is a job you can do yourself if you are comfortable on a ladder and willing to disconnect electrical wiring. The work takes two to four hours and requires basic tools: a screwdriver, a wrench or socket set, a stud finder, and a helper to support the weight. The hardest part is not the removal or installation—it is making sure the power is off and the venting is correct before you turn it on.
Before you buy a replacement, measure the space where your old microwave sits. Over-the-range models come in standard widths of 30 inches and 36 inches, and they must fit the cabinet opening and clear the cooktop below. Check the depth and height as well, because some models sit further forward or back than others. If your old unit is 30 inches wide, a 36-inch model will not fit, and forcing it will damage the cabinet.
You also need to know whether your current venting goes up through the cabinet into the wall (ducted) or recirculates air back into the kitchen (ductless). If you have ducted venting, your new microwave must also be ducted, or you will need to reroute the ductwork. If you have ductless, you can replace it with either type, though ductless is simpler because it requires no changes to the wall or roof.
Key Takeaways
- Turn off power at the breaker before you touch any wiring, and test the outlet with a voltage tester to confirm the power is off.
- Measure your cabinet opening and the depth of your old microwave before you buy a replacement, because over-the-range models come in fixed widths and depths that must match.
- Remove the old microwave by disconnecting the power cord, unscrewing the mounting bracket from the wall studs, and having a helper support the weight as you lower it.
- Install the new microwave by mounting the bracket to the same studs, sliding the unit into place, reconnecting the power, and testing the venting before you use it.
- If your old venting was ducted and your new microwave is ductless, or vice versa, you will need to modify the ductwork or install new ducting, which may require cutting into the wall or roof.
How to turn off power and disconnect the old unit
Go to your electrical panel and find the breaker that controls the microwave outlet. It is usually a 20-amp breaker labeled "microwave" or "kitchen." Switch it to the off position. Do not just unplug the microwave—you need the breaker off so that no one can turn it back on while you are working.
Use a voltage tester (a battery-powered device that lights up when it touches live wires) to confirm the outlet is dead. Touch the tester to the outlet where the microwave is plugged in. If it does not light up, the power is off. If it does light up, go back to the panel and flip the correct breaker.
Unplug the microwave from the outlet. If the cord is hardwired into the wall (no plug), you will need to disconnect the wires inside the junction box behind or above the unit. Take a photo of how the wires are connected before you disconnect them, so you know how to reconnect the new one. Black wire goes to black, white to white, and bare copper to bare copper or green.
How to remove the mounting bracket and lower the old microwave
Open the microwave door and look underneath the unit, inside the cabinet. You will see a mounting bracket bolted to the wall studs on both sides. Use a wrench or socket set to remove the bolts—usually four bolts total, two on each side. Keep the bolts in a safe place; you may be able to use them again.
Have your helper stand on a step ladder on the other side of the counter, ready to catch or support the microwave. Microwave ovens weigh 60 to 100 pounds, and you cannot safely lower one by yourself. Once your helper is in position, slowly pull the microwave toward you and down. The unit should slide out of the cabinet opening as you lower it. Do not let it hang by the power cord or any ductwork.
Once the old microwave is on the counter, disconnect any ductwork that is still attached. If the venting is ducted, you may see a metal collar or flexible duct connected to the back of the unit. Loosen the clamp or screws that hold it in place and slide it off. Set the old microwave aside.
How to prepare the cabinet opening for the new unit
Look at the mounting bracket that was bolted to the studs. If it is in good condition and the new microwave uses the same bolt pattern, you can leave it in place. If the new microwave came with its own bracket, or if the old bracket is damaged, remove it by unbolting it from the studs.
Use a stud finder to locate the wall studs behind the cabinet opening. Mark them with a pencil. The mounting bracket must bolt directly to the studs, not to the drywall or cabinet, because the microwave is too heavy for drywall alone. Most over-the-range microwaves have a bracket that bolts to studs that are 16 inches apart, which is standard in most homes.
If your new microwave requires a different bracket position than your old one, you may need to drill new holes in the studs. Use a drill bit that matches the bolt size (usually 3/8 inch). Drill slowly and use a level to make sure the bracket will be straight. If you are not comfortable drilling into studs, ask a helper or hire a handyman for this step.
How to install the new microwave
Position the mounting bracket on the studs using the bolt holes you located or drilled. Slide the bolts through the bracket and into the studs, then tighten them with a wrench. The bracket should be rock-solid with no movement. Use a level to confirm it is straight.
Have your helper support the new microwave while you slide it up and into the cabinet opening. The unit should rest on the mounting bracket. Line up any screw holes on the microwave with holes on the bracket, and tighten the screws. Do not force the microwave into the opening—if it does not slide smoothly, stop and check that the bracket is level and the opening is clear of obstructions.
Once the microwave is mounted, reconnect the power. If the cord is a plug, insert it into the outlet. If the wiring is hardwired, connect the black wire to black, white to white, and bare copper to bare copper or green, using wire nuts to find each connection. Wrap the connections with electrical tape. Go back to the breaker panel and switch the breaker back on.
How to connect the venting and test the microwave
If your new microwave is ducted, connect the ductwork to the collar on the back of the unit. Use a metal clamp or screws to find the duct so it does not come loose. If the ductwork is flexible, make sure it is not kinked or crushed, because that will block airflow and make the microwave work harder.
If you are switching from a ducted microwave to a ductless one, or vice versa, you will need to modify the ductwork. For a ductless conversion, you can cap off the duct that goes through the wall or roof with a metal plate and screws. For a ducted conversion, you will need to run new ductwork from the back of the microwave to the outside of the house. This may require cutting into the wall or roof, which is a job for a contractor if you are not experienced with it.
Turn on the microwave and run it on high for one minute with nothing inside. Listen for unusual noises and check that the venting fan is running. If you have ducted venting, go outside and confirm that air is coming out of the vent hood. If you have ductless venting, the air should come out of the grille on the front of the microwave. If the venting is not working, turn off the microwave and check that the ductwork is connected and not blocked.
Common problems and how to fix them
If the microwave does not fit in the opening, the cabinet opening is likely smaller than the microwave width or depth. Measure again and confirm the model number on the box. If you bought the wrong size, return it and order the correct one. Do not try to force a microwave into an opening that is too small.
If the microwave is level but sits too high or too low compared to your cooktop, the mounting bracket may be in the wrong position. Some brackets can be adjusted up or down by moving the bolts to different holes. Check the installation manual that came with the microwave to see if adjustment is possible. If not, you may need to drill new holes in the studs.
If the venting is not working after installation, check that the ductwork is not kinked, crushed, or blocked by debris. If the duct is flexible, straighten any kinks. If the duct is rigid metal, look inside with a flashlight to see if anything is blocking it. If the ductwork looks clear, the problem may be a damper in the duct that is stuck closed. Some dampers open automatically when the fan runs, but if yours is stuck, you may need to access it from the roof or attic and open it by hand.
Frequently Asked Questions
Do I need a permit to replace an over-the-range microwave?
Most jurisdictions do not require a permit for replacing an existing microwave with a new one of the same type and size. However, if you are changing from ducted to ductless venting, or if you are modifying the electrical circuit, some areas may require a permit. Call your local building department and describe the work before you start.
Can I install a microwave over a gas cooktop?
Yes, but the clearance between the microwave and the cooktop must be at least 13 to 18 inches, depending on the microwave model. Check the manual for the minimum clearance. If your old microwave was gas, your new one can be too, as long as you maintain the same clearance.
What if the new microwave is smaller than the old one?
If the new microwave is narrower or shallower than the old one, there will be gaps around it. You can fill these gaps with trim kits, which are metal frames that fit around the microwave and close the space. Trim kits are sold separately and must match your microwave model. Install the trim kit before you mount the microwave.
How do I know if my ductwork is ducted or ductless?
Look at the back of your old microwave. If you see a metal collar or flexible duct connected to it, the venting is ducted. If there is no duct, or if the duct goes to a filter inside the microwave, the venting is ductless. You can also look in the cabinet above the microwave—if you see a duct going up into the wall or roof, it is ducted.
Can I hire someone to do this work instead?
Yes. An appliance installer or handyman can replace the microwave for you, usually in one to two hours. The cost is typically 100 to 300 dollars, depending on your location and whether any modifications to the ductwork are needed. If you are not comfortable working on a ladder or with electrical wiring, hiring someone is a safe choice.