Thread: How to exhaust gas range/cook top?

I'm sure there are varying opinions on this, but I'm wondering what people recommend (if anything) when they run into a natural gas oven range/cook top that only has an internal fan over it (the typed incorporated into a microwave)? Do you recommend that an external exhaust be installed?

Thanks.

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No, I don't.

It seems it would need to be, but the recirculating type exhaust on the microwaves are considered approved by most AHJ.

rick

Report that the fan is a recirculation type, and does not vent outside.

The only time I recommend a hood at all is if the range has a grill top.

No exhaust fan venting to the exterior is required.

Mainly make sure there are proper clearances to combustible material above and to the sides, and the rear (the wall covering).

And exhaust to the exterior would be nice, but that could have a negative effect if make up air is not accounted for.

Make a recommendation all house guests stand in the kitchen and breath deeply during cooking. That should filter the air of CO and aerosolized fat leaving mainly CO2 and water vapor.

Not required but really and truly should be required to have a hood interlocked to the gas control and flow tested with combustion analysis.

Bob

For all recirculating fans, I mention whether it has a carbon filter installed or not.
Verbal, I recommend the carbon filter.
For gas, I recommend exhaust out.
Verbal, strongly recommend exhaust out.

My report states whether there is or isn't an X fan and whether it exhausts outside or not. I explain the pros & cons to the client during the HI.
Anything that is rehabbed usually has an X fan around here. Unfortunately they are always installed so well. I love finding the 600CFM X fan tied to 4" pipe or just into the joist cavity, happened a few times.

Originally Posted by Jerry Peck

No exhaust fan venting to the exterior is required.

Around here certain cities an exhaust fan to the exterior IS required. San Clemente is one.

Mike

Originally Posted by Jon Errickson

I'm sure there are varying opinions on this, but I'm wondering what people recommend (if anything) when they run into a natural gas oven range/cook top that only has an internal fan over it (the typed incorporated into a microwave)? Do you recommend that an external exhaust be installed?

Thanks.

Just to be clear.... there are microwave/vents that discharge outside.... and standard hoods that are re-circulating. From the way your post is written it could imply that all microwave vents discharge inside and all others vent out.

Matt --

When I originally posted the question (back in Feb.) I was wondering what, if anything, people recommend when they come across a gas cook-top or range and there isn't an exhaust vent to the exterior (maybe there's just an interior vent, like the re-circulating type).

Most if not all "microhoods" have the ability to be vented outdoors. Usually it involves following the manufacturer's instructions on removing the motor housing, rotating it and re-installing in the appliance prior to installation above the range or cooktop. Most can be vented to appropriately selected materials for venting out the backside or above. Although most come out of the "box" configured to recirculate. Most range-hoods come configured to exhaust, and can be configured to recirculate following manufacturer's instructions - generally involving a knockout, not a rotation of the fan housing, and oftentimes requiring the use of a different type filter.

Reviewing the size of the kitchen location for rough calculations of cubic feet area for fuel fired appliances, an enclosed (doors, etc.) galley type kitchen often times doesn't have free cubic feet (not filled by appliances, cabinets, etc.) sufficient to meet the minimum requirements for even combustion air, let alone make up air for an exhausting appliance, and in the presence of a central heating and/or AC system are often drawing this from that HVAC register. If an operable window is present - where local codes speak to the subject of venting for gas cooking appliance, will suffice then distance from cooktop can compromise the safety/efficiency of the cooktop burners. Enclosed small kitchens without windows (such as often found in older apartments and condo conversions, etc.) should have a means to exhaust, you'll find recommended by the appliance manufacturer, and references to the National Fuel Gas Code by one of several designations (ansi standard number, NFPA 54, etc.), possibly mention of International Fuel Gas Code, and mention of local codes, should they be more restrictive, and its Listing Standards and category code.

Making note of any/all of those conditions present (oftentimes such a kitchen was originally outfitted with an electric cooking appliance, retrofitted with gas later on) would be prudent.

Especially if you observe what appears to be a venting or exhausting appliance, that you have observed and checked function has been installed to recirculate, and not vent/exhaust - certainly should be noted in report.

I usually make a note of the range hood being recirculating brand and ask them to consider venting it to the outdoors in case the stove/oven does not burn cleanly and recommend a CO detector be installed per manufacturers instructions.

If the recirculating vent is a concern to the buyer, he can install a ceiling exhaust fan in the kitchen. This vent can vent to the outside, thus removing the discharge from the filtered, recirculating range vent. I see this combination of vents in numerous homes.

Condos usually do not have exhaust vents in the majority I see and often times design does not allow for vents to the outside wall in the same way some electric dryers need to use bucket traps for the same reason.

I simply suggest a Charcoal filter be installed.

Yesterday I saw a microwave/vent installation that was new to me. It did not have an exhaust route. It appeared that the motor was oriented to vent up and to the outside, but no opening in the upper cabinet existed and certainly no duct was installed. I looked outside and there was no outlet there. It was clearly not recirculating through the front of the appliance. Therefore, it appeared to be trying to exhaust against the bottom of the upper cabinet.

Darrel Hood
DILIGENT PROPERTY SERVICES

Originally Posted by Darrel Hood

Yesterday I saw a microwave/vent installation that was new to me. It did not have an exhaust route. It appeared that the motor was oriented to vent up and to the outside, but no opening in the upper cabinet existed and certainly no duct was installed. I looked outside and there was no outlet there. It was clearly not recirculating through the front of the appliance. Therefore, it appeared to be trying to exhaust against the bottom of the upper cabinet.

Darrel Hood
DILIGENT PROPERTY SERVICES

I've seen over a dozen of these. The installer did not orient the motor or divert to recirculate instead of exhaust. Just write it up as needing to be corrected. It's an easy fix.

Some of my Asian clients opted not to purchase because there was not or could not be an effective means of venting cooking fumes to the exterior.

Invariably, when I inspect a residence (stand-alone or condo) owned by an Asian I find a restaurant grade exhaust system installed (at considerable expense.)

I inform my clients about the true functionality of exhaust hoods. A significant percentage have been impoperly installed. (i.e. the diverter baffle is in the wrong position,etc. lots of noise but no effective discharge to the exterior)

Originally Posted by Bob Harper

Make a recommendation all house guests stand in the kitchen and breath deeply during cooking. That should filter the air of CO and aerosolized fat leaving mainly CO2 and water vapor.

Bob

Especially when cooking fish