Because we work in a college town (Go Gators!) and inspect a lot of student condominiums near campus, the over-the-range microwave receives close attention. It is a student’s second most-used food prep appliance—after the phone for ordering pizza. Microwaves get a lot of abuse, and don’t have a long lifespan. Also, the replacement units are usually installed by a handyman. So a student condo is an enhanced version of the microwave problems we find in a regular residence. Here’s our top 5 typical defects:

1) Does not vent to exterior - Microwaves come out-of-the-box set up to exhaust out the front and the baffle plate has to be adjusted and fan rotated to reconfigure for top or back exhaust, so it blows through a duct to the roof or out an exterior wall. A microwave that has ductwork in place to exhaust cooking fumes to the exterior, but has not been configured to do it by the installer, is a common defect. 

2) Not on separate circuit - The building code requires that a microwave which is fastened in place have a separate 20-amp circuit. Depending on the size, they are rated to draw between 8 and 13 amps. Other appliances operated at the same time can overload the circuit if the microwave is on a shared circuit. We test by seeing If the microwave still works when we trip the GFCIs at the countertop or the kitchen appliance breaker(s). It is not uncommon in a remodeled older house to find that the dishwasher and microwave are both on a single countertop appliance circuit.

3) Loose mounting - Even a mounting that is slightly loose is noted because, once it begins to loosen, the mounting deteriorates progressively with usage. 

4) Not functional - There are two kinds of “not functional”: a) completely dead, with unresponsive control panel, and b) sounds like it is working but does not heat a test cup of water.

5) Radiation leakage due to damaged door or handle - This is typically only a problem if there is damage to the seal around the door or the handle. We use a digital microwave leakage meter, shown below, and report if the leakage exceeds the 5.0 milliwatt threshold set by the EPA. A recent survey by appliance service technicians found that over half of the microwaves more than two years old have leakage at least 10% higher than 5.0 milliwatts. 

     A separate issue that is open to interpretation at this time is the height of the bottom of the microwave above the top of the range. The IRC (Interational Residential Code) defers to the manufacturer’s installation instructions regarding the correct distance. All the manufacturer installation manuals we have seen specify that the top of the microwave should be located 66 inches above the floor. This is, coincidentally, also the standard height of the bottom of a wall cabinet in most kitchens for installation of a range hood fan.     But an over-the-range microwave/fan combo is taller, between 15 and 18 inches high. When you deduct the 36-inch height of a range, the space between the top of the range and the bottom of the microwave is between 12 and 15 inches. If the controls are at the back of the range, most people of normal height cannot see the controls while standing upright, and have to lean down and reach over the hot range—just a few inches above large, and possibly boiling, pots—to change a temperature setting. 

    Conversely, the NKBA (National Kitchen and Bath Association) recommends that the bottom of the microwave be no more than 54 inches above the floor, which allows 18 inches clearance above the range. Otherwise, a shorter person would be reaching over their head to remove a hot item from the microwave—which is also dangerous. One building department jurisdiction in our area now requires an 18 inch clearance between range and bottom or microwave. We think that higher or lower should probably be determined by the needs of the occupants of the house.

    Also, see our blog post Do microwaves require any minimum clearances around them?

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Here’s links to a collection of some of our other blog posts about APPLIANCES: 

• What are the building code requirements for installing an appliance (furnace, air handler, water heater) in the attic?

• Which house appliances need a dedicated electrical circuit? 

• Is a washing machine drain hose required to be secured at the standpipe?

• When was GFCI-protection for kitchen dishwasher receptacle outlet first required? 

• Why does venting a clothes dryer into a garage, attic, or crawl space cause problems?

• Does a refrigerator water supply line require a shutoff valve behind it? 

• My spa tub stopped working. What's wrong?

• What is the maximum recommended height above the floor for an above-the-range microwave?

• Why would a home have natural gas appliaces but no gas meter? 

• Is a hot water faucet required at a washing machine?

• Can I remove a 240-volt range receptacle and hard-wire the range? 

• Can a dishwasher be wired to a kitchen counter small appliance receptacle circuit?

• Why is it bad to have a clothes dryer vent near an air conditioning condenser (outdoor unit)? 

• Do home inspectors test the appliances?

• Are a range and refrigerator required kitchen appliances for a house to pass FHA inspection? 

• What are the code requirements for an outdoor dryer vent cover?

• What is the maximum length for a clothes dryer vent? 

• Why are my ceiling fan blades drooping?

• How do you inspect a dryer vent? 

• Why is there a water hose connected to the back of the clothes dryer?

     Visit our APPLIANCES and COMMON PROBLEMS pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.