How about carbon monoxide poisoning.

This a gas fired appliance.

Where exactly are you expecting the products of combustion to go, other than into your lungs?

There are any number of options for downdraft venting which leave the cabinet unobstructed, including remote motor location.

What you are describing is an optional exhaust to the outdoors for cooking odors, etc. Residential gas ranges have no provision or requirement for venting. It is true that a "gas-fired appliance" (boiler or furnace) must be vented and that vent is normally connected directly to the firebox without a fan.

Some pseudo-commercial range salespeople have told me that ranges with burners over a certain output are required by law to have an exhaust system but I have never found such a requirement in any residential code and none of the salespeople has ever been able to tell me where they got that information. Anyway, it's mostly a matter of personal comfort and people have different tolerances for airborne pollutants.

If you don't want an exhaust system, be sure there is a window or door nearby so if it gets stuffy or if you burn something people will still be comfortable remaining in the kitchen (or the house in the currently popular all one room living spaces).

The downdraft ducts usually go down through the range, through the floor and across the basement ceiling rather than through cabinets.

Not venting is unappetizing. The steam, grease, and smoke gets on your ceiling, walls, and furnishings.

I thought the OP was referring to a downdraft exhaust vs. a conventional overhead one. No exhaust? You gotta be kidding me.

We had a 700 cfm unit that even removed the stench of mrs. worthy's tripe and fish.

its true, when i think about it, first off, my old electric range had a vent which just redirected the air to the front of the vent, no outside duct work, then the other factor was I think we used it 2 time in 2 years. plus add in the fact that my kitchen is 24X16 with 5 doorways & 3 windows in it plus an outside doorway leading to the rear deck, i think I am going to go with no vent.
thanks all who replied.

Its not just cooking odours a vent removes.

Moisture is generated both by the gas stove operating and by the heating and boiling of food on or in the range/oven.
Each person puts a couple of cups of moisture into the indoor air in a day. Each pet does as well. Steam rooms/showers, regular shower and bathing pump moisture into a house, not just the bathroom. Laundry contributes.

That moisture has to go somewhere...my suggestion is to remove it via a powered vent of some sort.

In this day and age, knowing what we know of HVAC, the issues of interior moisture, mould, mildew and such it amazes me how many still don't use fans or venting.

I'll take a half hour of noise over a mouldy home any day.
And there are plenty of options that make a range or stove top vent almost silent. Ditto with bathrooms.

I wouldn't live without powered venting, at least one of 90CFM per thousand square feet. I have no idea if that is code or best practice or not but that is what we do and we simply don't have moisture issues despite living in a temperate rain forest. If they are in rental homes they are wired in via humidistat so there is no option not to run them.

"I'll take a half hour of noise over a mouthful home any day."

A gas cook top in a residential setting is not run long enough to introduce significant moisture in to the house.

Even a gas oven does not run the burner 100% of the time it is turned on.

Check with your local building officials. Portions of code may or may not apply in your locale.

Some defer the requirement to have a vent to the appliance manufacturer, and that's dependent on cumulative BTU output of all of the burners being on at once.

Thus, if the appliance manufacturer says you need a vent, then "code" says you need a vent.

If you do need a vent, 2009 IRC does require makeup air be provided to the cooktop if the vent is over 400CFM. Makeup air can't be by opening a window. It's supposed to be mechanical, and automatic, whenever the fan is turned on.

Are these portions of the code enforced? Not usually. Most AHJs, as well as most builders, aren't even aware of them.

A lot of this is coming about as building envelopes get tighter and tighter, as well as part of LEEDS certification requirements.

This thread started out by confusing venting and ventilating and it seems to have continued.

In this discussion a "vent" is for the purpose of allowing the byproducts of an enclosed gas-fired appliance to pass to the outside of a house without mixing with the air in the house. It is not normally required but it is possible to vent the oven of a gas range but it would not be possible to vent open cooktop burners.

In this discussion an "exhaust" is for the purpose of removing some portion of stale, smelly, or otherwise objectionable air from a house. An exhaust is normally required over an open-top gas broiler but not for a gas range unless the manufacturer requires one.

The 2003 IRC regulates range hoods in Chapter 15, "Exhaust Systems" and the venting of gas appliances in Chapter 24, "Fuel Gas".

"I'll take a half hour of noise over a mouthful mouldy home any day."

A gas cook top in a residential setting is not run long enough to introduce significant moisture in to the house.

Even a gas oven does not run the burner 100% of the time it is turned on.

If you read the entire post, you would see that it isn't the moisture from just the gas appliance I was referring to.

That same exhaust fan which is removing steam from boiling pasta, food odours and the like is also exhausting moisture laden air from bathing, respiration, pets, aquarium, etc.

Its no wonder things like air fresheners and Febreeze are so needed. Houses without powered air exhausting that is used must just be stale and not so fresh. I guess you get used to it but I'd not live in one.

"Air fresheners and Febreeze" introduce more unwanted odors into a house IMHO. However, tolerance for chemical masking odors is often determined by an individual's sensitivity to smell which is greatly influenced by their sensitivity to taste. When using chemical masking odors you should be aware that about a quarter of the population has the capability to find such odors to be overly strong.

A range exhaust would not normally be used often enough to have a noticeable effect on moisture or odors in a house. If you need ventilation for comfort you should add an automatic system including an energy recovery unit. Modern HVAC systems can combine heating, cooling, hot water, and ventilation in one unit with very effective controls.

I currently have a microwave/exhaust fan over my electric cooktop. I plan to remove the wall upon which the microwave is attached. It is vented through an upper cabinet by a duct through to the outside. Would it suffice or be "code" to replace it with a small fan system, similar to bathroom fans, in the place where the duct goes outside?

Why not a normal island hood, as opposed to a downdraft system? That would leave your base cabinets free and clear, and it would also do a better job of venting (heat, smoke, smells etc. rise, so it is easier for a hood to capture them than it is for a downdraft system).

I have a cooktop in my island and a downdraft telescoping vent installed with a remote mounted fan. I lost a minimal amount of cabinet space and am able to vent to the outside. This is important since I don't want my clothes, my house or guests smelling like fried fish, sauteed garlic or other cooking odours. Personally you'd be doing yourself a disservice by not installing some type of venting option.

"That same exhaust fan which is removing steam from boiling pasta, food odours and the like is also exhausting moisture laden air from bathing, respiration, pets, aquarium, etc. "

Not enough to matter for the limited time it is used for clearing cooking odors.

Steam is the least of the problems from cooking, oil and grease end up all over the place.