Wow! A rare case where the aesthetics part of the performance-aesthetics-economy: pick-any-two limitation is not a factor in hood selection. But first, given a sealed household, I would strongly recommend obtaining a furnace kit to use outside air. This will avoid the possibility of the MUA system not working perfectly and the hood causing negative house pressure and hence backdrafting of the combustion appliance. I know that such devices exist for Beckett burners, and would guess that there are adapters for other burners. As the OP correctly notes, a 200 cfm ERV is not going to cope with a 1200 cfm vent hood. (Actually, what would happen with a sealed house is that at full power, the hood would pull the cfm the ERV would let through into the now minus a couple of inches w.c. house pressure.) So MUA is essential, and in the mid-Atlantic region would be pretty uncomfortable in winter if unheated. Depending on one's tolerance for heat and humidity, cooling in summer might be optional or not. We are starting to get into the realm where performance-economy, pick any two is applicable. MUA can be roughly characterized as passive or active. By passive is meant no fan in the circuit. Active uses a booster fan to keep the house pressure stable. No-fan only works for simple ducting with a vent hood air flow controlled damper. (A recent post here provided some sources for these.) If a filter is used at 1200 cfm (or whatever flow actually could be pulled with all the doors and windows open, then the house pressure will drop. One can see on websites selling filter packs that the pressure drop at such flow rates is too large for combustion appliance safety, which require negative pressures not be greater than 0.03 to 0.06 inches depending on appliance type. Active is needed to overcome the filter restriction. It may be needed to overcome heating heat exchanger restriction and/or air conditioning heat exchanger (expander) restriction. The difficulty with active is balancing the MUA air flow rate against the variable hood flow rate such that the house pressure is near zero. This usually requires a control system of some sort, and can be a "project." What to do? What to do? Only one free-of-processing-controllers active MUA has occurred to me. In the simplest embodiment, the hood control is connected to two parallel wired identical fans, one in the hood exhaust path and one in the MUA path. Then the two will (try to) operate at nearly the same flow rate at every control setting, and one only needs to adjust the MUA duct restriction until it matches that of the hood path. More exactly, adjust the MUA path so that house pressure falls very little as the hood is turned on. Note that this doesn't account for bathroom fans, fireplaces, or other exhaust flows not due to the hood. In such cases, PID control of the MUA fan would be needed. In my case, due to a 1500 cfm hood, 1000 cfm over-oven vent, fireplace, and three bathroom fan household, I am building an active MUA that will use an axial blower in the 2000 cfm regime. It has to overcome the pressure loss of its intake vent, its filter, and its heat exchanger (which is hot water pumped from my oil burner). Control is via a Fuji PID controller operating from a BAPF differential pressure sensor. The motor power control is not yet selected, and a lot of sheet metal action is still needed, along with further attic revisions that I seem to have trouble getting to at the needed rate. I recommend the OP and/or his HVAC person read the "Kitchen Ventilation Systems Application & Design Guide" that may be found at Greenheck's web site. It periodically moves around, URL-wise, so a Google search by name may be fastest. Greenheck or one of its competitors may be able to provide what you need for considerably less agony than a do-it-yourself HVAC project would. kas

Your builder is supposed to know. Contract the hood to a COMMERCIAL installer and they will make sure system is right. My experience with commercial kitchens has been that make up air is provided intergal to vent-a-hood. There is no reason for tempering air in the comfort system when air can be drawn in ajacent to range. Hopefully that answer's your question,here's mine. Are you acting as your own GC? If you are and haven't started yet you should reconsider because there will be far rougher roads ahead concurning the build. If you have a GC and haven't started,hire a new GC.

Adam with that much CFM on the blower, if you stand to close you might get sucked out hahaha, only joking.One question did they use the right size ducting material that the manufacture recommend if undersized this could be the source of your problem.

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