Range Hood CFM Reducer
DCJersey
11 years ago
Featured Answer
Sort by:Oldest
Comments (16)
gwlolo
11 years agoRelated Discussions
1200cfm oversized hood...Overkill for 30" BlueStar range?
Comments (47)Well, "any" is potentially a very small amount, and I'm sure that there is some slight amount. My attic, however, is vented all around the periphery, at the ridge, and also with an attic fan housing. Ice dams at the roof edges tend to occur when the outside air warms up during the day and heats the snow bottom up through the vents instead of top down. In my present half-completed configuration, the ~ 2 x 2 ft heat exchanger sits above a Cooley and Hart 3 x 3 diffuser in a hall ceiling. There is a furnace filter taped down on top of the heat exchanger. This style of filter (Honeywell Filtrete) needs significant pressure drop to move much air through it, and I was pleased to observe that warm air doesn't seem to rise through it in the winter, or hot attic air settle through it in the summer. The sides of the heat exchanger and its plumbing are buried in insulation. When kitchen fans are running and the house is closed up, air is pulled through and the thermostats, the larger-than-typical-size Taco pump, and the furnace controls do their thing to heat the air. (The circuit is capable of well over 100k BTU/hr depending on furnace and air temperature.) The problem, as I have pointed out a few times here, is that pulling air through a filter and heat exchanger requires a pressure drop -- a drop too large for combustion appliance safety. My only combustion appliance is an oil furnace, and it now uses its own MUA system to avoid back-drafting. Nevertheless, if I were to run both kitchen fans at once at full power expecting all flow to be made up through the heat exchanger without fan boost (possibly 1400 actual cfm with restricted MUA), the pressure drop in the house causes some furnace exhaust to be pulled into the house via tiny cracks not normally relevant when there is a positive draft, so I don't do dat without an opened window. My intention is to duct the heat exchanger to a mushroom air intake already installed on my roof via an axial in-line fan and a four-inch pleated filter caddy so that at the maximum possible flow rate (possibly 2000 cfm, say) the house pressure can be balanced and all the MUA comes from outside without mingling with the attic air. A damper may be needed, although as noted, the Filtrete coating will be pretty resistant to air passage without some deliberate pressure drop from the in-line fan. kas...See MoreWhat should be the minimum CFM for a Wall Range Hood
Comments (10)The formula used for determining hood CFM is: Total BTUs (add each burner BTU up) divided by 100 5 burner example 14000+12000+9500+9500+7000= 52000 BTU 52000/100= 520 CFM (min), Next, if the hood should have open space inside to tap smoke and heat before it is exhausted, commercial style slats trap grease and do not reduce airflow as screen mesh does, as are easy to clean. If the hood is over a island you will need to over size it due to cross breezes, Example 36" cook top would use a 40" hood, (not a 36"). As for noised reduction when operating may I suggest the following options: Oversize the cfm ( i.e. ranges calls for 520 CFM, use a 1000 or 1200 CFM) and run at a lower speed which is quieter. Use double squirrel cage fans abd not the flat blade fan. Or, mount an external fan at the top of the stack on the roof or just under the roof inline, which will reduce noise. (be sure to have a damper that closes when off in the stack to prevent downdrafts when the fan is off. Note, if on a outside wall do mount to remote fan to close, as it will radiate the noise even loader. The farther away from the hood the better. While I have not tried one, but the reviews on the "Z-Line" hoods have been the best I have read, and seems everyone who owns one is happy and feels it was a good value purchase. You can see their full line at http://stores.zlinekitchen.com/StoreFront.bok I hope this is useful to you. Here is a link that might be useful: Z Line Hood...See MoreDo I need make up air with a 300cfm island range hood?
Comments (14)Wow! Some basics are needed here. First, no air goes up the hood, through the duct, and to the outside that didn't get into the house. Seal the house and the hood flows no air. Second, the hood will try to move air and if it can't the house pressure will fall to the zero CFM value at the left edge of the hood blower's fan curve, perhaps a few tenths of an inch of water column. This pressure, and likely the pressures corresponding to a good portion of the fan curve (less the losses from hood filter to outside), can cause back-drafting of combustion appliances. Back-drafting is a carbon monoxide hazard. Some combustion appliances can back-draft at a mere 0.03 inches of water column. Fireplaces are just a bit higher than that number, depending on draft achieved. Third, while low CFM levels may be supplied by the house leakage as make-up air, this is not usually good for the interiors of house walls, and can pull dust into the interior. Fourth, there are many ways to supply make-up air (MUA) and generally some heating of the air is needed (possibly required by code) in northern climes. Fifth, the comments about wall vs. island hoods are valid, but the result is somewhat confusing. Without a back wall, the island hood needs to be larger front-to-back (deeper) to accommodate the rising expanding cooking plumes it is to capture from the rear burners. This larger area still requires the needed flow velocity (90 ft/min suggested), so island hoods will in general require more CFM than the same performance hood mounted to a wall. (Feet per minute equals CFM per square foot of hood entry aperture area.) If drafts are accounted for, including those caused by moving people, the island hood may need to be wider as well as deeper. In some cases, cold MUA can be brought into a room having an oversized heater (think Modine type) and preheated that way. In others, an electric or hydronic heat exchanger may be needed somewhere in the MUA ducting. Low CFM requirements might be addressed by an existing hot air furnace, but usually these are sized for normal house heat loss. In all cases, even in houses with separate MUA for combustion appliances, the MUA configuration should be imagined as having ducting commensurate with that needed for the hood system. Last, all of the above is related to having a hood that removes most of the cooking effluent, leaving the walls clean and the air relatively odor free. As far as I know, there is no Code requirement to keep one's house clean and thus the options of no hood, or of a barely filtered recirculating hood, or a barely useful low CFM exhausting hood are available choices....See More300cfm Hood vs. 600cfm Hood Requiring Make Up Air?
Comments (11)It would be best to start any quest involving kitchen ventilation to study the literature, or at least study the many many threads here on the topic. I would prefer to write answers to questions that are based on my possibly inadequate previous writing than generate yet another long message covering the entire topic. You may wish to start with the "Hood FAQ" which can be found by searching. I believe it is listed under @opaone. Hoods are about capture and containment, and success in this depends on many factors, the most critical of which is sufficient air flow velocity at the hood entry to ensure that which is captured is contained and expelled from the residence. This velocity is independent of how many burners are running at once, but rather what the cooking surface temperature is plus plume heat augmentation by gas burners. In any case, the 100 CFM per 1000 BTUh is derived from certain standardized commercial hoods, not residential hoods. See the Greenheck Guide available at https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf for comparison between the 100 CFM per rule of thumb and the hood aperture velocity rule. I suggest 90 CFM per square foot of hood entry aperture, and this aperture needs to be large enough to overlap the rising and expanding cooking plumes. Let me adjust the salesman's statement: "...because the design pulls more air than a filtered/baffled hood of the same [zero static pressure rated] cfm [when hanging unattached to anything in free air]." Ventahood use squirrel-cage blowers that also perform the function of baffle filters, thereby eliminating that cause of pressure loss. However, as blowers go, they are more susceptible to other pressure losses than conventional blowers, and hence if there is extensive ducting, or inadequate MUA, their flow rate will be less than the actual rate asserted. My guess is that you should have a 24 x 42 inch hood aperture, requiring an actual 630 CFM obtained from a 900 - 1000 CFM rated blower. Read MUA related threads to determine how closely the interior air pressure has to match the exterior air pressure for safety. Your state may require heated MUA. There are a lot of ways to accomplish MUA under these conditions, and the threads here should help you understand what you have to tell us to allow better tailored help. kas...See MoreDCJersey
11 years agohuango
11 years agoUser
11 years agoDCJersey
11 years agoSparklingWater
11 years agoweedmeister
11 years agoTmnca
11 years agocooksnsews
11 years agoFori
11 years agoa2gemini
11 years agospringplanter
11 years agoSparklingWater
11 years agoSparklingWater
11 years agomrclancy
11 years ago
Related Stories
KITCHEN APPLIANCESWhat to Consider When Adding a Range Hood
Get to know the types, styles and why you may want to skip a hood altogether
Full StoryMOST POPULAREasy Green: 23 Ways to Reduce Waste at Home
Pick from this plethora of earth-friendly ideas to send less to the landfill and keep more money in your pocket
Full Story5 Stunning Modern Range Hoods
Today's kitchen range hoods can look like sleek sculptures. Here's what to look for when you go shopping for one
Full StoryKITCHEN DESIGNWhat to Know When Choosing a Range Hood
Find out the types of kitchen range hoods available and the options for customized units
Full StoryKITCHEN DESIGNHow to Choose the Right Hood Fan for Your Kitchen
Keep your kitchen clean and your home's air fresh by understanding all the options for ventilating via a hood fan
Full StoryKITCHEN DESIGNHome Above the Range: Smart Uses for Cooktop Space
With pot fillers, shelves, racks and more, you can get the most function out of the space above your kitchen range
Full StoryKITCHEN DESIGNHow to Find the Right Range for Your Kitchen
Range style is mostly a matter of personal taste. This full course of possibilities can help you find the right appliance to match yours
Full StoryHOUSEKEEPINGHow to Clean Your Range and Oven
Experts serve up advice on caring for these kitchen appliances, which work extra hard during the holidays
Full StoryKITCHEN DESIGNModern Storage and Sunshine Scare Away the Monster in a Kansas Kitchen
New windows and all-white cabinetry lighten a kitchen that was once dominated by an oversize range hood and inefficient cabinets
Full StoryKITCHEN APPLIANCESThe Many Ways to Get Creative With Kitchen Hoods
Distinctive hood designs — in reclaimed barn wood, zinc, copper and more — are transforming the look of kitchens
Full Story
juliekcmo