Piggybacking this one because I'm in the same boat.

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

Thank you kaseki! Questions:

1. The synchronized fan solution sounds good, however it may affect air temperature in the kitchen too much. Heated MUA can add at least $1k or more to the project and is more expensive to run. Do you know if there's a way to set up controls for the makeup fan to kick in only past say 100 CFM? You can probably get the first 100 CFM from the ERV, etc.

2. Do you know of electronics/controls that can be purchased to control these things, i.e. when the damper opens/fan kicks in, manual override, etc.?

3. What can be done to lower the CFM required for proper ventilation? Lower the hood? Perhaps there are more obscure but also more efficient designs you would recommend looking into?

4. Do you know how to choose / where to find a fan that allows for low CFM, such as say 50? Or perhaps they all do?

5. Are there instruments/ways to measure the actual CFM upon installation?

Thanks,

Nick

1) Since the goal is keeping the house pressure from going too low, better would be a differential pressure sensor and a relay to inhibit MUA below some pressure, such as 0.03 in.

2) I am building my own. A real HVAC person who works in commercial buildings would be a possible source of knowledge on this.

3) I don't understand the question unless you mean how small a cooktop would it take only boiling water to avoid MUA altogether. Restaurants, by the way, have to use MUA, and they spend most of their electricity cost on venting, air replacement, and air heating/cooling. Once you select the 48-inch range (with the implication of using it) and a grill (massive effluent), you are into the realm of approximating commercial cooking, if only for shorter periods, and the whole cooking package requires a big, powerful hood and MUA.

4) Most induction motors run at low speeds when controlled by a suitable controller, even the simple diac/triac configurations (such as my Wolf hood has). Just be sure you have a continuous control, and not a "n" position control. Keep in mind that effluent rises at about 3 ft/second, so if the air velocity at the hood aperture is significantly less, containment is unlikely.

5) I think yes. Well, of course, but I'll interpret the question to mean easily accessible means. There are people who measure how tight a house is by replacing a door with a panel having a calibrated fan and differential pressure sensor. Such a setup could be used to compare negative pressure at known flow rate to negative pressure you get when the door is sealed and you run the hood.

I suspect your HVAC person needs to consult with one who has more experience for your particular situation. That isn't me.

kas