MUA - Make up air for range hood
scottvd
13 years ago
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beekeeperswife
13 years agobreezygirl
13 years agoRelated Discussions
MUA - Make up air for range hood (cross post)
Comments (1)without any information about local weather extremes it is hard to make any comments. What works in the middle of the country can be a complete disaster in the north (cold winter) or south (hot summers)....See MoreMake up air vent location for range hood?
Comments (16)In order to begin to understand it, you would need to buy ANSI Z21.1 for about $650. There is some very technical engineering, even though it doesn't look like it, in the ventilation between walls of the oven and cooktop sides that ensures that the cabinets up against the range will not get hotter than 194°F. If you block the airflow by lowering the range (some people try modifying the feet for thin countertops that make them less than 36" tall), or putting ducts in for MUA, the outside wall of the range will get hotter. If you force that much extra air through the range, (push or pull) you change the way the gas burns, and create CO problems. Even if you can adjust the air shutters to compensate, you would then have to turn on the entire system just to make a pot of tea, in order to get enough air to get a clean burn. With holes in the floor or back wall, the natural draft intended/engineered to cool the outer walls of the range can be disrupted or diverted, leaving the heat to build up around the range - nothing to do with heat in other areas of the home. What can't tolerate more heat than the wood cabinets around the range? Another separate reason for no holes is the possibility of a gas leak. How much gas do you think that duct will hold, just waiting for someone to create a spark? The testing standards do not say no holes "unless someone thinks of some unusual excuse"....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 MoreAnother MUA - make up air challenge question(s)......
Comments (1)MUA should really be provided mechanically, not through “drafty” walls, crawl spaces or attics. The hood you are purchasing should provide you with the volume of MUA that is required to run the system efficiently, assuming it is correctly sized with your gas range. Your log stove should have its own MUA system, but if you are relying on the hood system, it needs to be sized to accommodate both the log stove AND your gas range. The International Building Code for Residential Construction should provide all of the details you need (in the mechanical code) for this system - even if your local jurisdiction or contractors are not familiar with it....See Morewarmfridge
13 years agoJon T
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13 years agoJohn Liu
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13 years agoJohn Liu
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13 years ago
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