Again, I urge you to read the many MUA related threads in this [Appliance] forum.

Integrating MUA into furnace or AC systems is perhaps the most difficult approach. They aren't sized for this function.

I also don't want to address all possible MUA systems until you specify your hood flow rate based on some rationale.

MUA only works when the hood is on, and it only needs heating when the MUA is on and it is winter.

MUA can be passive or active. These terms refer to presence or not of a blower in the MUA. See the picture I attached to your other thread. That duct is the MUA duct and it has heating and a blower.

How long you will keep your hood operating at higher blower power requiring MUA is something only you know, but for most the power cost is negligible. The cost is in the components and adaptation to the house.

Residential hood do not usually include any MUA features. Commercial hoods can. Read the Greenheck guide.

Yes this is a HVAC issue.

Fantech has some MUA systems scaled for residential use.

Thanks, kaseki, this makes me feel more informed for when I meet with contractors.

We're not looking for professional-grade appliances, but to avoid grease build up, a slightly more powerful blower would be nice (around 600 CFM?).

90 CFM/sq. ft. x hood aperture area (sq. ft) x 1.5 for pressure losses = blower rating

Thanks. Does that calculation include things like bends in the ducting or length of the duct? My range will not be on an exterior wall, so it will need a 90 degree bend and about 6 feet of ducting in the attic. Would that require a more powerful blower?

I don't know much about residential MUA, but it seems there are at least three basic decisions:

1) conditioned (or tempered) MUA or not

2) If (1), do you need an energy or heat exchanger

3) local MUA or distributed

Let me give you an example from my world. Laboratory fume hoods, like range hoods used to just suck conditioned air from wherever they were located in their leaky buildings. The first one that I worked at in Philadelphia had MUA coming in from right above my head as I worked in front of it. It was not conditioned or tempered. In the winter, a hat was desirable. In the summer, the ice in my ice bucket keeping my enzymes cold in the hood melted very, very quickly.

The least expensive MUA in operating and maybe installation costs would be right very near the source of the "problem", probably grates in the floor or counter near the range or cooktop. It would be air straight from outside run through a physical filter. You really want something like an air curtain around the appliance so it does not mix with room air.

If there is enough air being exchanged and mixed with conditioned air to make it economic you want an energy recovery or heat recovery exchanger. The choice between them depends on humidity and what you need to do with it.

If you are to temper the incoming air, it needs to run by your HVAC systems. Your situation is unusual because you have two separate systems. At that point, with forced air, you are not local anymore. Sometimes in residential forced air, MUA runs through a dehumidifier but is not cooled before being dumped into the duct distribution system. If so, when the cooling kicks on, it is fully conditioned.

In your situation, you have to heat with resistance heat if going for lowest installation cost. If you use another fuel for your boiler that is lower cost (natural gas yes, fuel oil or propane, maybe not) it may pay to run the MUA through a small hydrocoil if you feel you need it. Depending on the nature of your boiler and remainder of your hydronic heating system, you may need a buffer tank in your system or it might not be able to support such a small load without short cycling the poor boiler.

Here is an idea for you. If you already have an indirect water heater tank on that system, perhaps that could be used as a buffer. You might be able to just have the circulator pump for the indirect tank kick on and run water through the hydrocoil, but you'd want to be able to valve it off during the summer. If you propose this to a hydronic heating person that is not particularly smart or creative, they may look at you like you are from Mars. I think it would work, but may have never been seen on this planet.

NJ Mom: The factor of 1.5 is to account for the blower's fan curve vs. the flow rate dependent, and mostly unreported, pressure losses. The source of these include:

• o How good is the MUA system at keeping the house pressure close to that outside
• o How much pressure loss is there across the baffles at the actual achieved flow rate
• o What is the pressure loss of the hood interior transitions

The duct pressure losses can be calculated, but the pressure losses listed above usually exceed the duct losses and are a matter of guessing. Also, the fan curve varies for each blower. So I have chosen a rule of thumb of 1.5X. It may not apply to Vent-a-Hood systems because they don't have baffles, but do have a blower type with a less robust fan curve for resisting the pressure losses outside the control of their hood design.

NJ Mom - Do you currently have issues with cooking and using your existing hood? If not, I think I would skip the MUA and go for a nice 400cfm hood.