Writing in generalities, one approach is to provide MUA to the furnaces so they don't get back drafted from negative house pressure. In some cases this can be done by tailor made or factory made hardware directly to the furnaces. In other cases the furnace room would be sealed from having an air path to the kitchen. If possible, which depends on heating type, this would address the safety issue. The VAH flow rate then would be determined by how negative the house pressure got with whatever leakage the house and air conditioning has. A kitchen MUA could then be added if necessary to get good hood flow. You may want to condition this air. This is the bigger bucks part of the problem. Either furnace hot water has to be diverted to a heat exchanger in the air path (if the heating is hydronic), or electric resistance coils used in the airflow. Adding another furnace for the occasions of high vent flow is overkill because, unlike a restaurant, the periods of high flow would be a small part of a day. The kitchen MUA has another issue -- normally one wants to filter out critters and bugs and even dust from the air duct, and this causes a pressure drop. In such a case the MUA will not be making up as much air as desired unless a blower is added to the MUA path. Now there has to be a scheme for controlling the blower. However, if not conditioning or filtering the air is acceptable, then a large duct to a diffuser with a damper controlled by detecting hood air flow is a simple, low-cost solution. Broan makes a unit for this, or DIY using one of many Honeywell motor controlled dampers is an option. I suggest reading or at least skimming the literature linked at my "my clipings" page. In particular, Greenheck covers the topic well, albeit from a commercial point of view. But the commercial POV is the one that led to the Pro-style ranges and counterpart ventilation systems we are addressing with MUA. Last, while I think HVAC solutions other than another furnace are options, the more DIY one gets solving MUA the more one is trading one's time versus paying for a slightly more expensive turn-key system. But at the 10K price point, even with a hands-off goal, I would look for other bids/approaches including HVAC companies concentrating on restaurant HVAC systems. kas

This is an issue that requires some measurements and some analysis. To even know where you are you need to measure the pressure in the house relative to outside the house as a function of different settings of vent air flow and MUA air flow. Either hire someone to make the measurements or buy (cost is fairly modest, as I recall) a differential air pressure device. In test kitchens, the means of introducing MUA is via a perforated wall some distance from the test stove/vent air handling equipment (hood). What is desirable is that the MUA, when it gets to the air volume between the cooktop and the hood entry aperture, be relatively non-turbulent. Introducing MUA at one's feet next to the stove may or may not achieve this. Often the toe kick spaces there are too small, and may, depending on configuration, aim at some other structure (wall, island, whatever) that will force the air flow up. Now there is turbulent air all around the cook and the hood. I think the MUA exit area(s) should not be too much smaller than the hood entrance area unless the MUA injection point is fairly far from the hood. In a (completely burger odor free) burger joint in Concord NH there is a CaptiveAire system in which the MUA is expelled downward from the ceiling in front of the hood. (This aperture is actually part of the hood assembly.) I would estimate that the MUA aperture is roughly half that of the typical very large commercial hood aperture, although I cannot see all of the hood aperture from the customer seating area to be very exact about this. In my residential configuration, a 3 x 3 foot ceiling diffuser is used about 20 ft down a hall from my 10 sq. ft. aperture hood. This hall delivery should slow down the air velocity to about 37 ft/min, which is a slight breeze -- less than a half mph. I haven't pressurized the MUA yet, but I have seen the effect of an interior split cycle air conditioner head spilling air toward the hood, there is significant plume displacement. Is your MUA source via a basement, or via the roof? It might be better if you dumped the MUA at the ceiling directed away from the hood such that the air takes a longer path to the hood aperture. Or dump it into diffusers at various locations in ceilings connected to the kitchen. (This might be a casus belli if not heated.) Or use a lot more toe kick area. Besides measurement, I would check that with windows open, MUA off, and hood on, that you can cook something and see it fully captured and contained by the hood system. Then as you close up windows, and do whatever you are doing (manually?) to set MUA flow, does this start interrupting the capture efficiency? And yes, if you don't have a closed loop controller then both hood and MUA should have continuously variable controls. By analysis I meant making a gross estimation from the hood system fan curve and the properties of your vent system of what flow rate you may be achieving. (There are contractors who can measure this by temporarily replacing a door with a measurement device.) Ditto for the MUA system. What is its fan curve vs. ducting, filtering, diffuser pressure loss, and heating scheme, if present? If your actual replacement air is 200 CFM, then ideally you want the MUA to be 200 CFM less than the hood can pull when the house pressure relative to outside is zero. One expects that if the house pressure is positive, more air will flow out the hood system. But in your case I suspect, as did opaone above, that there is really a lot of turbulence around the hood and this turbulence is interfering with the cooking plumes attempting to rise to the capture area (the hood entry aperture). kas

Don't assume HVAC pros will be well schooled on this very complex need. The collective knowledge on this forum, led by Kaseki, is greater than most HVAC individuals. I also have a 48" Blue Star and if you are wanting to use it to it's full potential you will need a sophisticated exhaust system with make up air and perhaps forced and conditioned depending on your climate. 1200 cfm should be adequate, but if you use a remote blower you can and should go a bit higher. I think I spent close to $5k on my MUA system, parts and install. I needed it fan forced and heated, I'm in Chicago. Here is what I bought: https://shop.fantech.net/en-US/muas--1200--makeup--air--system/p111242 If I would have listened to my well experienced and great in every other way builder, I would have had no MUA and an ineffective system. If I would have listened to my builder after I insisted on MUA, I would have spent $1500 for an ineffective MUA system that would have also taxed my furnace. My builder wasn't trying to get one over on me, they just didn't know any better and thought my house was leaky enough given its age. This is a very common thought we see on these forums. In the end, I told them forget it. Then I called my long time HVAC guy. He had done this in restaurants but never residential, though was up for learning something. Fantech provided really good support and I was also extremely lucky that this could be installed after the fact w/o having to tear things up. My venting and MUA system work great together and I can wok, sear steaks on cast iron and notice little to no residual grease, odors or smoke.

"The manufacturers of Vent Hoods are miseducating the consumers." Yes. Somewhat. Not really. They are in business to make money and they do that by making hoods as inexpensively as possible and then selling as many as they can for as much money as they can. Their goal is NOT your health or the IAQ of your home - that is up to you. Telling consumers that they'll also need to spend money on MUA if they buy hood X will negatively impact their sales (ignorant consumer will just go buy a hood from brand Y instead because it doesn't say you need MUA even though it has an identical need for MUA) so they do not want to do that. MUA is also not something that fits well within consumer hood manufacturers world except to the extent that they might offer a hood w/ integrated front curtain ducting. It is much more of a pure HVAC thing. It can be supplied to the return ducts of an HVAC system, the supply ducts or ducted directly to appropriate locations. Incoming air can be heated by gas, electric or hydronic. Incoming air may need to be humidified or dehumidified. It often needs to be electrically integrated with the HVAC system controllers to function properly. Consumer hood manufacturers - ARE NOT IAQ or HVAC people or engineers - they make something decorative that by nature must include air movement so they reluctantly include air movement in their product. Commercial hood manufacturers - ARE IAQ and HVAC people and engineers. Their customers are much more educated than consumers. The one singular purpose of the product they are selling is IAQ - so they design and sell systems that provide good IAQ. Aesthetics is quite secondary for them. Residential HVAC companies in the U.S. - ARE NOT IAQ people (they should be though). A tiny few, less than about 1%, know it well and a few more know it a very little but the vast majority know just enough, based on what they've been told at a 4 hr CEU course, to sound like they know what they're talking about but they don't really understand it. Most residential HVAC people do not understand air movement or why things are done the way they are - they only know how to use tables that tell them to do this or that and as soon as something is outside of defined parameters they're totally lost (though sometimes don't even realize that they're lost). Licensed Professional Engineers do (or most do, some don't) understand air movement and other elements. They are the people who create the tables that HVAC people use. They can think independently. Defined parameters for them are not tables but the physics of air - it's movement, temperature and components. Unfortunately, most U.S. engineers do not have a good understanding of human physiology (except perhaps for biomedical engineers). They do not, for instance, understand how CO2 functions in our bodies and how high levels of CO2 due to poor ventilation affect us. Or how poor ventilation resulting in high levels of VOC's, PM, Carcinogens and Pathogens affect us.