If the cooktop or range is against a wall, then the amount that the hood aperture extends past the burners front-to-back should be commensurate with the amount the hood overlaps the burners side-to-side. This is because the rising effluent expands equally in all directions as it rises. (A powerful hood will cause some distortion, but nominally and for the most part practically, the hood air flow does not "reach out" and suck in air that already has a velocity that dominates the air velocity of the hood intake air away from the actual aperture.) The best insertion of make-up air (MUA) is any method that doesn't cause any cross-drafts at the hood. In test kitchens, this is done by introducing MUA through porous walls. We can generally exclude this approach for residential kitchens. Floor, wall, or ceiling registers (diffusers are what you want for air flowing out, but are not really suitable for floors) are all potentially suitable options. Mine is a ceiling diffuser located down a hall that leads to the kitchen. This provides some flow straightening and area expansion as a means to minimize cross drafts. Cost of heating MUA is not high, but the assembly of parts needed may be high in cost. Unless you operate your hood 24/7 boiling off maple sap, you likely will only be running the hood at partial to full power for short durations. I have a heat exchanger hooked to my hydronic heating furnace that can utilize all of its (forget the exact number) probably 180 kBTU/hr output if needed for MUA heating. I think the furnace at this rate uses 1 point something gallons of oil per hour, so this high cost is around a few dollars an hour for usually less than an hour when the exterior temperature requires the maximum temperature correction. In any case, I believe that an electric heater in the MUA path will be an easier thing to integrate. Cost per hour may be higher in proportion to your electric rate's higher cost (per BTU) over oil. You may have to run significant power from breaker box to heater if you are going to make-up very high flow rates through the hood at -20F. (Fireplaces can have high flow rates that have to be made up also, but I don't know anything relevant about the flow rates of gas fired fire places, so that should be something you can find out for planning purposes.) If you are rugged enough, the MUA heating doesn't need to be perfect in temperature control, just good enough to keep the introduced air tolerable during the cooking. Your code requirement doesn't provide for different conditions needed for safety, it just mandates MUA. The safety requirement that should be driving a more sophisticated MUA requirement, applicable where combustion appliances are used without their own separate MUA sources (ducts to outside, operation in a closed room ventilated to outside, or whatever), is to keep the internal house air pressure high enough to not back-draft the appliances, and thus avoid pulling carbon monoxide into the house. For unblown gas appliances, the house negative pressure limit is 0.03 inches of water pressure, and requires very low pressure loss in the MUA system with a powerful hood. I think this is necessary for fireplaces also, as they depend on the draft for flow, and the draft depends on the pressure difference between hearth and top of chimney, given hot flames to provide upward momentum. All this means is that you can either provide a code-compliant MUA system that is rated for a given flow rate, and for safety do whatever is really needed to safety proof your combustion sources, or provide an MUA that is sophisticated enough to keep the house pressure up over the range of ventilation flow rates possible with the hood, fireplace use (potentially high flow rates themselves), bathroom fans, etc. While I am working toward a closed-loop pressure controlling MUA system for myself, I am certain that for most needing MUA, isolating appliances is the better cost approach, allowing the MUA to aid hood blower performance, and not be so critical for safety. My oil burning furnace does have its own MUA, but I wouldn't operate my fireplace with my kitchen ventilation running at full power, even with windows open (due to pressure loss in the screening), without a powered MUA path. Can't help with an educated HVAC company, but FanTech has a line of powered MUA systems (don't recall if they are heated). If not, a suitable heater can be found and inserted into the duct path. Someone on this forum back in the 2008 to 2010 period, possibly clinresga, provided an image of his basement ducting with coil electric heater in the path. My [not yet completed] system is in my attic and draws air from above the roof. A blower will push this air through a filter, through the heat exchanger (think car radiator), and into the diffuser. HVAC companies dealing with restaurants will understand what you have to do, but often their setups are not compensating -- flowing a fixed MUA flow rate against fixed vent hood flow rates. Large building MUA is usually compensated, but the schemes used are better suited (as far as I've been able to learn any details) for continuous pressurizing MUA systems that have to compensate for outside door openings. They can do this with passive air pressure control of dampers that recirculate MUA around the blower. The blower motor runs continuously. The relatively recent of introduction of residential MUA requirements has provided some impetus to development of residential MUA systems, so availability of systems and components should be expected to increase. Keep reading; be sure to check out the Greenheck paper available at their website: KVSApplDesign_catalog.pdf, as well as CKV_Design_Guide_2_031504.pdf, available somewhere on the Internet. These are commercially oriented, but should provide useful insight. kas

Since the structure isn't going to deflate and collapse when an exhaust system is running, the amount of air that goes out an exhaust system is limited to how much outside air comes in the structure at other places. A make up air system is a great approach. All houses need regular fresh air anyway, both purposes can be served. Older houses are usually not tight - think not only around windows and doors, but through the walls (electrical sockets and switches, pipe runs through walls and similar unsealed breaks in the wall, through the floor up from a crawl space or basement, unsealed areas around HVAC return or supply grill boots, etc.). Unless all of these have been sealed. It's not often done other than in extreme weather areas. In times of mild weather or otherwise, cracking a window to allow in fresh air helps an exhaust fan (whether for cooking or even in a bathroom) work better. Gas appliances if inside the structure should be in areas that are closed off from inside air so that backdrafting can't happen. In my house, I have two "closets" (one for a water heater, one for a furnace) that are within the exterior walls but both closets have outside air supplies and exhausts and the doorway edges are sealed tightly with raised threshholds and tight weatherstripping around the door frames. When gas appliances are in a basement, the best approach is to similarly close them in an airtight room or otherwise closed off with outside air supply for combustion.

Is this a passive (no blower) or an active (blower) MUA? Do you have any combustion appliances that take air from inside any part of the house connected to the kitchen? If not, then the pressure loss in the MUA from using a decent air filter will not matter, safety wise. Please better explain the path the MUA would take from outside to kitchen with option 1. I would like to be sure that I understand the concept. Also, do you need to heat the MUA? (See chart.) Dumping MUA into a basement or laundry room provides a means for having a heating system (e.g., hydronic or electric Dayton wall unit) in the room with its own thermostat, eliminating a complexity in the MUA system. In either option, MUA entering the kitchen must not cause excessive turbulence or cross drafts in the area between cooktop and hood entry aperture. Commercial MUA dumped at the floor seems to work OK with commercial style cooking devices (which are mop-spaced off of the floor). However, some home ranges prohibit air entry below the unit. This needs to be checked. Else, air from either source may have to be passed into more remote (from the cooktop) registers/diffusers and allowed to spread out into the kitchen volume. Option 2 needs to be considered from a dust into the kitchen concern point of view. In any case, the air intake outside should be higher than ground level, with the duct going down to the level where it would enter the basement.

"Thank you, Kaseki! I’ve been reading your past posts-would you mind sharing again what cooking device/range hood/ makeup air system you chose and why?" You may find images of elements of my kitchen in various posts. I won't repeat them here. Also, some hood flow parameters may be found in FAQ I. Please note that my kitchen reno planning began in 2007, with most purchases of appliances made at the end of that year. Delivery was taken significantly later for most items, but well in time to confirm measurements and interface details. Explaining rationale would make this tediously long, take too much of my time, and jack this thread. I owe a kitchen photo to the FAQ II thread, and one or more should appear in the fullness of time. The cooktop: I have two induction cooktops, a 36-inch Frigidaire Gallery (replacing a 36-inch Electrolux clone Kenmore that failed after 5 years or so) and a Cooktek 3500W induction wok. These are set in soapstone over cabinets in which there is added stone support and wire racks for pans, providing maximum air volume for cooling. The hood system: Overspreading these is Wolf's largest Pro Island hood set at 34.5 inches above the counter. The hood connects to a damper, then a Fantech silencer, and then a Wolf (Broan) 1500 CFM roof blower (which has a damper). (As I have explained many times, once installed in a hood system blowers cannot flow their rated CFM due to pressure losses. I have measured, however, about 1000 CFM with presently passive MUA and no other household exhaust blowers operating.) Duct is 10-inch. The secondary hood system: There is a secondary system comprising a pair of ceiling registers (14 x 20 if I recall), 3M Filtrite filters in the register boxes, a damper, silencer, and roof mounted NuTone down-blast blower. I believe this blower is rated 600 CFM, but can't find my literature for it as it was originally bought to provide additional flow for a '70s cooking center with miniscule blower performance. The registers are ceiling mounted over a pair of Wolf wall ovens. The MUA: I have planned an active MUA system, but all parts have not yet been acquired. There seems to be no end to new "required" projects. The system as it presently exists is operated passive, and comprises a highly ventilated attic with an additional roof-mounted down-blast commercial blower housing for eventual ducted air intake, a one-inch pleat 24 x 24 furnace filter (to be replaced with a lower pressure loss 4-inch pleated canister version, a 30 x 30 heat exchanger connected to my oil-fired hydronic heating system, and a 36 x 36 diffuser at the end of a hall that connects to the kitchen. The control system for this is intended to keep the kitchen pressure equal to the outdoor pressure (which will be the attic pressure once the MUA is ducted). Some elements of this are place. A Fuji computer module in a DIN control array next to my furnace will attempt to adjust its natural frequencies (poles and zeros) such as to make a stable MUA system independent of the main hood flow rate, the wall oven vent flow rate, and bathroom blower flow rates. The differential pressure sensor upstream and motor downstream control loops are 20 mA current type. Separate sensors and controls are used to keep the heat exchanger from freezing when not in use and otherwise keeping the air passing it temperate. Blower will be the largest that can get into the attic that Fantech sells that incorporates the 10 Vdc control voltage motor. (I forget the part number.) This wasn't available back ca. 2010, nor did Fantech list a motor controller that could handle that size motor back then. If starting from scratch, I would investigate the present offerings of Electro and Fantech to minimize my work, but large flow rate in an assembled unit would likely not fit into the attic without removing the diffuser and heat exchanger for a one-time installation. While balanced air pressure is highly desirable for several reasons repeated often on this forum, I should note that my System 2000 oil furnace has its own MUA and a sealed exhaust stack installed within the original brick chimney that served the previous one- and two-generations-back Beckett boilers. The hot water storage is heated via a hydronic loop on the furnace, and the dryer is electric. Hence, back-drafting of combustion appliances is not an issue. To deal with the flow to the MUA heat exchanger (capable of 120k BTUh if necessary) as well as the longer reaches of my house hydronic plumbing, I use a larger (higher head vs. flow rate) Taco pump than is usual.