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My microwave venting is not working Over my gas range. I have no access to vent outside. Is there any type of heavy duty filtering vent available to mount under the microwave or to the wall under the microwave? That will not trigger my fire alarm?

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  • What is actually wrong with your vent not working? What problem are you actually seeing? Dec 17, 2023 at 13:37
  • @Triplefault I suspect the OP has a VTR setup, which is really no venting at all.
    – Huesmann
    Dec 17, 2023 at 13:40
  • Most places a gas range requires an actual outside vent to meet code.
    – Ecnerwal
    Dec 17, 2023 at 14:29
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    @Ecnerwal as far as I can tell it is extremely uncommon for code in the US to require external venting on natural gas ranges. It is almost universally recommended however.
    – jesse_b
    Dec 17, 2023 at 14:42
  • Challenge: I have no access to vent outside. Really? How far is the gas range from an outside wall and/or from the roof? In a quick check of one microwave/hood, it listed 140' "equivalent" - each bend or other change in the ductwork counted as 'x' feet, but there is clearly capacity for setups other than "range up against an outside wall". Dec 17, 2023 at 17:23

3 Answers 3

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Is there any ... filtering vent available to mount under the microwave or to the wall under the microwave?

If the filter does not fit into the microwave itself as part of the standard equipment of the microwave, then this is not a wise idea or possibly dangerous to add a filtering device under the microwave. The add-on filter would be within the space expected to be free above the cooktop, may restrict movement of pots and utensils, and may be too close to the burners for fire risk.

Since:

  • Smoke may be a concern: "That will not trigger my fire alarm?"
  • Venting outside is not possible: "I have no access to vent outside."

If your microwave has built-in ducting capability which could have been used to vent outside if your home had the facilities, you can add an inline duct filter (web-search) to the output of the ducting setup on the microwave:

Vivosun inline duct filter AC Infinity inline duct filter

(not affiliated or endorsing, only examples)

Attach such a setup to the output of the microwave duct, and vent it inside the cabinet above the microwave or an adjacent cabinet. A screen panel on the cabinet door may be required to let the filtered air out, and an inline booster fan to overcome the back pressure on the microwave fan may be required.

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Unfortunately a range exhaust that vents internally is never going to work "great" however they make charcoal filters specifically for internally vented range exhausts. Typically the filter would just be a steel mesh that catches some oil but not very much smoke. The charcoal filters do make a noticeable improvement in performance but need to be replaced more often as they are not washable.

An example of a charcoal filter: enter image description here

Versus what you normally find in a range hood: enter image description here

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  • No good for gas range - does nothing for CO or CO2 and therefore gives a false sense of security. Dec 17, 2023 at 14:48
  • @manassehkatz-Moving2Codidact: While one could very easily argue that CO2 is a concern with gas stoves (NO2 is actually a much bigger concern but still supports your point). It is not actually required to vent externally. Also OPs has already said they cannot vent externally which could be a literal physical limitation in construction, and that their concern is smoke not CO2.
    – jesse_b
    Dec 17, 2023 at 14:50
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You Need to Vent Outside

A cooktop exhaust fan takes care of several things:

  • Smoke
  • Cooking odors
  • Steam
  • Carbon Dioxide
  • Carbon Monoxide

The first three can be handled by a good filtering system.

The last two can NOT be handled by any filtering system, at least not anything available to an ordinary consumer.

Carbon Dioxide

Carbon dioxide is a normal byproduct of natural gas combustion. It is not harmful in small quantities - after all, there is always some in the air and humans produce it all the time. However, it is dangerous in large quantities. If you don't believe me, see the problems on Apollo 13. A good exhaust fan will help remove combustion air that includes carbon dioxide and fresh air, with less carbon dioxide, will come in to replace it. A fan that does not exhaust to the outside will simply recycle the same air, constantly increasing in carbon dioxide concentration.

Carbon Monoxide

Carbon monoxide is an odorless, deadly gas. It is far more deadly than carbon dioxide. It is not produced in significant quantities in normal use of a gas cooktop. However, it is produced if there is incomplete combustion, and that can happen if a burner is not functioning properly - e.g., due to spills. Carbon monoxide in small quantities can cause various symptoms that can easily be confused with the flu or other illnesses, in larger quantities it kills. A carbon monoxide detector is very helpful, and advisable in any home with combustion appliances of any type, but venting combustion air to the outside can prevent most serious problems from occurring.

Many "fire alarms" are really smoke and/or heat detectors. Some include carbon monoxide detectors as well, so if you are getting "nuisance alarms" it is worth investigating to see what they are detecting - if they are detecting carbon monoxide then you have a serious problem.

Never say "can't vent outside". OK, that may be the case if you are in a submarine or in an underground cavern or similar, and I don't recommend combustion appliances in those places. But for the vast majority of houses, the issue is not "can't" it is "expensive to do so". But usually quite possible with a bit of work. where there's a will, there's a way.

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  • Houses are not airtight vessels in space and if your stove is releasing alarming levels of carbon monoxide venting is not the solution, replacing the stove is. Anyone with gas appliances should have CO detectors and it's quite uncommon for smoke detectors to also detect CO strictly due to the confusion you mentioned where you might not know why the alarm is going off.
    – jesse_b
    Dec 17, 2023 at 15:16
  • For alarming levels of carbon monoxide, fixing the appliance is the solution. But venting can help significantly in minimizing the risks. Many modern houses are much more airtight - not my house with its 1950s windows, etc. But to the degree that forced ventilation - ERV or HRV - is needed. Dec 17, 2023 at 15:30
  • They absolutely are "much more airtight" but code strictly guides how airtight they can be for the exact reason of CO2. A gas stove emits significantly more CO2 than a human but it is accounted for in the airflow calculations, similarly maximum capacities of a building. A gas stove emits about the same amount of CO2 as around 20 humans at rest per hour, which would likely still be within the acceptable capacity limits for an average US home. Or 10 humans for 2 hours, etc. Also the exhaust vent just vents gasses it doesn't really help getting new oxygen back in which is the real concern.
    – jesse_b
    Dec 17, 2023 at 17:48
  • Nobody will question that exhausting dangerous levels of carbon monoxide is safer than not exhausting it but range hoods have been shown to not actually be very effective at it. And that is like saying "If you're going to run a gas generator inside it is safer to open a window" That is absolutely true but bad advice. Anyway I would never question that having a range hood externally vented is safer than not having it but driving a volvo is safer than driving any other car. If someone asks how to patch a hole in their honda tire I wouldn't say "Throw your car out and buy a volvo"
    – jesse_b
    Dec 17, 2023 at 17:51

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