Most modern microwaves use recirculatory venting and don’t have to be vented. However, if you have either a microwave above the range or want to keep food smell to a minimum, you might want to vent your microwave.
Venting microwaves on an interior wall normally means installing a ventilation pipe. That might vent to the central ventilation or meet up with the range hood ventilation – depending on your kitchen. In most cases, that’s a simple matter of installing a ventilation pipe and linking it to your existing system.
Main Topics
5 Reasons Why Venting a Microwave is Important
If you’re considering venting your microwave, there are plenty of reasons why it might be necessary. The four below include the most common.
Removing Food Smells
Recirculating microwaves can result in food smell buildup. That can cause issues for anyone with sensitivities to smell. Even if you just want your kitchen to smell fresh, ventilation can help. Most importantly, if you have a combi-oven, that will matter even more. Recirculating microwave ovens simply push hot air out of the vents into the kitchen, while sucking in new air. Of course, that’s usually pushed through a filter, but your home will still smell like anything being microwaved. And in some cases, that’s a really bad thing.
Heat Management
If you’re trying to keep your cooling bill low, venting your microwave outdoors can help a great deal. That’s especially true if it’s on for longer periods of time. So, again, this is more important if you have a combi oven.
Preventing Moisture Buildup
If you’re installing your recirculating oven inside a cabinet, it’s crucial to add ventilation. Otherwise, the airflow will cause condensation. Why? Air exiting the microwave is a lot warmer than air outside the microwave, so it will condensate and cause moisture buildup. Vents will ensure your cabinet stays dry.
Installing an Over-the-Range Microwave
Over-the-Range microwaves are old-fashioned but still available in a lot of shops. If you buy one, it’s intended to replace the range hood over your stove. This allows you to save space in your kitchen, by moving the microwave over the stove. The range-hood-microwave features ventilation in the back, allowing air to pass through – effectively taking the same role as the range hood. And, most importantly, it should connect to any ventilating you have in place for the range hood. If you don’t have any, you’ll have to install ducts and vent them outside.
Local Building Codes
Installing a range hood microwave might fall under local legislation. For example, U.S. building codes require that you vent kitchen exhaust outside. If you’re using a range hood microwave over the stove, it is kitchen exhaust. You might have to install ventilation to comply with building code. That is important for safety, because recirculating kitchen exhaust can result in dangerous fumes. It can also be important for selling the home – as you’ll have difficulty doing so if your kitchen doesn’t meet code.
Things You Will Need to Vent Microwave Through the Wall
If you’re venting a microwave, you probably want to either take it through a wall or through to your existing central ventilation. Making the decision should depend on where your central ventilation is or if you have any installed at all. You will need:
Tools:
Measuring tape
Chalk
Power drill
Phillips #2 bit
Saw / Power saw (Hacksaw and skill saw for best effect)
Level
Stud finder (optional)
Eye protection
Tin snips if not using adjustable venting
A ladder
Supplies:
Duct pipe that fits your range hood microwave – This varies considerably in size so you’ll have to check your make and model. E.g., it can be round or rectangular.
Elbows and fittings as necessary. E.g., do you have to turn corners with the duct? Do you want to change it from round to rectangular or square or vice versa?
Any duct covers as desired
Vent collar
Vent Cap or Hood if you’re installing in the wall or roof
Sheet metal screws (usually 1”, Phillips #1)
Venting Microwave on an Interior Wall: 5 Easy Steps
If you install a microwave on an interior wall, you’ll have to take your duct pipe across the wall or up to the next floor. Your decision to do so should entirely depend on existing ventilation installed in the space.
Check Ventilation Options
Unless your home is new, chances are, it already has ventilation. This might be existing holes in the wall. It might also be an existing duct line for a range hood. Or, you might have a central ventilation pipe running up through the house, to the roof. Check what ventilation options you have and where they are.
If you don’t have any, you’ll have to cut a new hole. Doing so means choosing whether to vent into a wall or into the roof. However, this is largely a personal consideration – although you might want to ask for a professional opinion in case local building codes show a preference. In addition, some local codes might not allow you to cut a hole in your own roof. You might need a licensed contractor to do so. Venting into walls is less strict. However, if you are in an urban area, you normally have to extend vents out.
Vents extending through a roof must extend at least 12” above the roof. Vent terminals extending through a wall should not be closer than 10 feet from a lot line and should be at least 10 feet above the ground level. And, in most cases, if you live in cold climates, you want to use gabled vent installation, where the vent comes out and then faces downwards, to prevent cold air from seeping in through the vent.
Once you know where you can run the vent, you can decide how to install it. In most cases, that should be:
The clearest and most direct line, against a wall, to the point of the ventilation
The duct should be unobstructed in its path. However, some people prefer to run ducts through cabinets to hide them.
A duct can be a maximum of 50 linear feet long, with each elbow counting as roughly 10 linear feet. So, if your central ventilation is too far away, you may have to vent into a wall anyway. Or, you may have to install additional fans.
Find the Studs
Use a stud finder, take off the sheetrock, or otherwise find the studs in the wall In most cases, these are 2’ apart throughout the entire home. This means that if you find one, you can calculate the rest using a tape measure. For example, you can measure from the corner. However, there’s always a chance that your home is not installed to standard, which might mean the studs are off.
Use a pencil or a carpenter’s pencil to mark where the studs are. Then use the pencil or chalk to trace the line where the duct should install. Measure the length to ensure it’s not too long. In addition, you want to keep turns to a minimum. So, you’re likely running your duct from the center of an interior wall, around a corner, to an exterior wall. You might then go up or directly out the wall. Your options here are normally to extend the duct pipe up to the ceiling, to run the duct along the ceiling, and then to make the final turn at the next wall.
Cut Necessary Holes
Mark and cut necessary holes for the duct. In most cases, you want to make holes slightly larger than the duct itself. If you’re installing ducts inside cabinets, you can also get vent collars to fit inside the holes. These cover the holes and seal the duct against the cabinet, to prevent it from rattling around.
In most cases, the easiest way to cut duct holes is to use a section of the duct to trace a hole. Use a level to make sure it’s level. You want the length of the duct and the width of the duct to be level for the hole. Do not cut into wall studs. Most duct pipe is about 10” across, which means you’ll have plenty of room to run between the studs.
Use a skill saw for large, basic holes that will have a cover over them.
Use a drill with a spade bit to start a small hole and then use a jigsaw if you want precise holes.
Finally, if you’re venting directly through the roof or through the wall, you can immediately install the caps to prevent water, birds, or other pests from coming in.
Install Attachments for the Ventilation
Most vent ducts are installed on hooks or racks. This will entirely depend on which type of ducts you purchased. Install these using a power drill, ensuring your screws are drilled into the wall studs. Make sure you follow any specific instructions that come with the ducts you purchased.
Install the Ducts
Fit the ducts into place, starting with the duct against the microwave. In most cases, you’ll have to install the first vent duct and then fit the microwave into place. Why? Most range hood microwaves vent to the back and you won’t have space to fit a duct in once it’s installed. Make sure you have someone on hand to help you.
Fit the ducts together and use either clamps or screws to secure the ducts to each other. When you get to the wall, use a duct cover to hide the hole on the interior side. You’ll have to fit the final piece from the outside. This should include a vent hood or cap, extending out far enough from the wall to meet local code. In most cases, that also means ensuring it is at least 10’ off the ground.
Special Note:
If you’re running your ducts to central ventilation, you’ll need a Y split for the ventilation. Make sure you check the size of the existing ventilation. Then, when you get your duct to the ventilation, usually inside the wall, cut the primary ventilation shaft, install the Y split, and install both the microwave vent and the original vent to the same pipe.
What is a Self-Venting Microwave?
Most modern microwave ovens use recirculating venting. This means they recirculate air into the kitchen, normally after passing it through a filter. Nearly all modern microwaves fall under this category. This means that it contains a fan which pushes air out of the microwave, creating a vacuum, which sucks new air in. This keeps the whole thing cool enough to function. However, it does mean that your kitchen will smell like anything you happen to be microwaving or baking.
Frequently Asked Questions
Venting an over-range microwave can be a lot of work. Chances are, you still have questions about how to do it. Hopefully, this FAQ helps.
How much does it cost to vent a microwave outside?
That fully depends on how far your microwave is from the vent and what your home is made of. In addition, if you’re in an urban area, local city code might force you to hire a contractor to do the work. Check local code and then take steps yourself. If you’re doing the work yourself, already have the necessary tools, and only have to run ducts 20 or so feet, you’re probably looking at roughly $50 in costs. If you have to install multiple elbows, additional fans, and run the duct 40 feet, it will cost more than three times that.
Do you need a vent for over the range microwave?
Yes. The U.S. building code, specifically the IECC Section R403.6 Mechanical Ventilation, makes it mandatory to vent kitchen exhaust outside. If you don’t vent your over-the-range microwave outdoors, you are in violation of that code. While that presents long-term problems like difficulty selling your home, it can actually be dangerous.
Can you use flex duct for a microwave?
You should not use flex venting for a microwave because it can increase your chances of fire. Why? Grease collects in the joints which can cause buildup and eventual fire risks. Most microwaves strongly recommend that you use a rigid duct instead. That’s important, because microwave vents are closer to the initial heat source than range hoods – meaning they are more likely to pose a fire hazard if something does go wrong.
Conclusion
Most microwaves don’t require venting. However, if yours does, venting it from an inside wall is a simple matter of running the duct pipe to the nearest external wall. Alternatively, you can choose to run the duct pipe through the wall to the central ventilation.
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