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Question DetailsAsked on 6/9/2014

Range Vent: I want to add a downdraft vent to my cooking range. What are my options?

The range is in the middle of the house and is not adjacent to an exterior wall (about 8 feet from it). Would it need to exhaust outside the house? What kind of workman do I need to for this job (contractor, appliance repair, anyone else?)

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2 Answers

Voted Best Answer

I have never seen one of this type that does not exit the house. You would not want the grease dumping into your basement, even with a filter it will happen.

The greater part of your job will be carpentry as if there is a wall behind the stove a hole will have to be cut up through the basement into the wall up to the stove. Unless it is one of the stoves that allows for it to fit inside a cabinet below. To answer correctly most here would be a picture of where this project is being done. I have done motorized ones that extend up out of the counter when in use and then retract. Those exit through the cabinet and require the cook top is to the front of the counter and not a drop in one

As an added note these tend to be better as they do not pull the heat away from the stove top when in use as much as the ones flush with the stove. I have install quite a few and happen to have an Amana cook top with built in down draft and I have to shut it of to get water to boil on the back burners.

A carpenter will know what can be cut and what not in the basement, a sheet metal contractor should know as well but at the other end for the finish by the stove they might not. Most carpenters that do kitchens have installed the minimal amount of duct work for this. They just have to be carefull with the number of ellbows and the lenght of the duct.


Answered 6 years ago by ContractorDon


Yes, exhaust it to the outside. some appliance guys and/or hvAc contractors would know how to proprly vent this.

The size of the exhaust vent should not be reduced , same size from the dowm=ndraft to the exit of the home,two or three elbows maximum. This will help keep the "airflow' near it's rated flow, restriction of the exhaust duct will limit the air flow to a point that it will not exhaust properly. due to the location, it will need to vent through the basement or crawl space,if yoor home is built on a concrete slab, vent from overhead not downdraft.

Choose your installer before you buy the downdraft!


Answered 6 years ago by BayAreaAC


1) Downdraft vents do not work anywhere as well as overhead vents, for the simple reasons that the ventis not directly over the source and also the airflow over the range is upward because hot air rises, so to be anywhere near as effective as overhead vents/draft hoods the airflow (hence fan power) has to be MUCH greater. Also, downdraft vents pull the air over the range and down around it, resulting in a lot more grease and moisture buildup on and around the range, and as mentioned in other posts requires a lot more heat from burners to cook because there is a lot of cooling on pots and such as well as direct removal of heat from burners from the airflow across the range top.

2) Overhead (updraft) vents commonly run in the 300-800cfm (cubic feet or airflow per minute) range for a normal stove - to get equivalent removal of fumes/grease/smoke with a downdraft vent behind the stove can take 1000-2000cfm, and for behind the stove popup vents I saw one study that said anything less than 15mph airflow across the stovetop does not work, and that can mean 2000-4000cfm units - which make a very noticeable draft around the stove, plus of course much more noise and electricity comsumption. The duct velocity for a 1000-2000cfm downdraft unit (largest residential sixed units) can run over 50-100mph in 6 inch diameter vent pipe, and even in 8 inch vent 30-60 mph. That makes for a LOT of noise not only at the vent but also in the exhaust pipes, so you need to sound insulate the ducts and provide vibration dampening at mounting points - and by law, the insulation has to be fireproof, so usually rock wool insulation. The normal downdraft unit that has enough power to actually do anything noticeable is loud enough that you cannot carry on a discussion in the kitchen while it is running. Some units rise only 6-8 inches above the stovetop level, so most of the vapor and grease vapor pulled toward the unit actually flows over the top - I have seen ones where boiling water vapor poured over the top of the vent like fog over the hills in San Francisco, with very little going into the vent itself. Even the tallest popups only rise about a foot or a bit more above the stove unless you custom-build a popup rack to hold the popup unit (making a sleeved double popup), so count on using the rear burners for boiling or frying to have a prayer of catching more than a small fraction of the fumes, which then means the good portion of that which does not get exhausted ends up on the stovetop and wall and cabinets below and around the back of the stovetop. One other recommendation - because of this buildup at the back, I recommend front control knobs if using downdraft venting ot reduce knob faillure from water and grease contract - which introduces child hazard issues with the front knobs.

3) There are ventless types for both overhead and stove-area vents, which use filters to remove the particulates and suspended grease fumes and such and then recirculate the air into the room. These are inherently less efficient than exhausted ones because a good portion of the returned air just goes right back up into the unit, rather than pulling fresh air around the stovetop into the unit. These ductless units require FREQUENT cleaning of filters (like weekly or more often commonly, as opposed to a couple of times a year for vented units), and need multi-stage filters to truly remove what will otherwise become persistent odors and grease spread through the kitchen air with the exhaust flow. This cleaning resultsin more grease through your sink or dishwasher too (commonly several gallons a year of grease, and as much as 10 or more gallon per year in some ethnic households where pan or stir frying or deep frying is common, so results in sewer issues from grease buildup too. Also becomes a serious fire hazard if filters not cleaned frequently, and airflow (hence air cleaning) is rapidly reduced as filter gets clogged with grease and household lint and floating human and animal hair in the air. I definitely do NOT recommend them, particularly if you have any frequency of frying or stovetop broiling or cooking with hot oil.

4) Either type also available in the normal outside ducted and exhausted configuration (which I STRONGLY recommend) - duct size and allowable run lengths detailed in owners manual /installation instructions, and if venting horizontally rather than up through roof increase airflow 10% or so - more with long runs of duct. To avoid grease buildup in ducting avoid bends as much as feasible, and where bends are needed try to use sweep elbows rather than regular elbows, and I use seam sealer (an automotive product) to seal joints on any horizontal or downward runs to prevent any grease accumulation inthe ducting from leaking and staining drywall ceilings or walls or causing an in-wall fire hazard and stink.

5) Be sure exhaust point is at least 3 feet (minimum by code, more in some areas) from doors or windows or building / HVAC air intakes, and cannot be in attic or basement or crawlspace by code, plus that would stink those areas up and cause mildew/mold/rot from the large amount of moisture. To avoid putting moisture and grease into attic, preferably to vent through roof if feasible rather than out wall overlain by eaves, otherwise as far away from eaves as feasible, or better yet extend duct (insulated in cold climates) under eaves/soffit to beyond roofline, though that is a bit unsightly.

6) During a general remodel the General Contractor may install himself depending on experience - otherwise an HVAC contractor generally does this, though in some areas Electricians handle the installation.

7) Some general rules of thumb for sizing your fan - the 3 different rules of thumb (you take the highest number from the three calculations) say 1 cfm airflow per 100 Btu of range output (including stovetop broiler or fry surface and oven) at maximum use, secondly 100cfm per lineal foot of greater of stovetop or vent hood/collector width, thirdly air changes calculation where you compute volume of room and divide by four, so for example 12x15' kitchen with 7 foot ceilings would yield 315 from this calculation. Again, you take the HIGHER of the three numbers you get from the 3 calculations above. Different requirements in some code areas. For island installations you increase highest number of above three by 50%, for downdraft units there is no fixed rule of thumb but I have heard and use triple the above 3 computed numbers to get a reasonable chance of at least partial functionality.

Answered 6 years ago by LCD

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