Thanks, kaseki, for your interesting insights. Intuitively it seemed better to me that the air was 'pulled' down by the inline fan, rather than pushed down the duct by a hood fan, but I understand your point to be that it fundamentally is irrelevant where the fan is mounted.

I am ignorant of our condo's water column pressure. It seems fairly well built and reasonably tight, so maybe I need to install an air make-up vent. Our hot water tank is on an indirect zone with our oil boiler, and the clothes dryer in the basement is electric, so those devices don't draw any air. The boiler gets outside air via its two-channel exhaust duct, which exits out the sill of the building, just as I am considering venting our range hood.

Inches of water column is a unit of measure of air pressure relating to a fraction of the approximately 33 ft that a water column at sea level in a tube sitting in water open to the air at the base will rise to if a vacuum is pulled at the top of the column. See also pascals.

For tiny fractions of sea level air pressure, the blower doesn't much care where it is in the air circuit, any more than a resistor in series with a battery cares which side of the battery it is wired to as the current in the loop will be the same. When significant fractions of air pressure are involved (including in the vicinity of the blades), then we are in a non-linear range where position can matter, although usually the blade design is selected to cope with position.

Be sure the MUA source outside is at least 10 ft (preferably upwind) of the vent exhausts.

Kaseki, thanks again.... Do you think I'll be able to pull about 300 CFM from the hood if I use a 600 CFM inline blower, given the ducting situation I'm working with?

I would guess so assuming an MUA system or open window.

Not sure if he said it but you will be limited by your duct size. See if there is room for a 3.5 x 14 duct in that wall. If a condo you probably can't change it.

A good suggestion by weedmeister.

The answer to resulting air flow rate will depend on the blower chosen as well as the restrictiveness of the ducting. For example, the Wolf 801640 Broan-NuTone exterior blower flow drops to 300 cfm at about 0.7 inches w.c. (some of which includes fan housing loss). The Broan 331H exterior blower is similar in performance. But the Broan RM325H interior blower drops to 300 cfm at 2 inches w.c.

http://www.broan.com/common/productDigitalAssethandler.ashx?id=c6cb8514-86ed-49f2-bb1e-9c5443ad495c

The former two blowers are intended for 10 inch duct, while the latter is intended for 8-inch duct. Fan curves for in-line blowers may be found as tables on Fantech's web site.

At 300 cfm, I would expect the hood baffles to cost around 0.3 inch w.c., although this is a stab in the dark as this information is almost never available except for commercial hoods where HVAC analysis is expected and required, and in any case the commercial filters will have been optimized for pressure loss and. grease collection efficiency, while residential filters will have appearance and fabrication cost dominating the design.

(A higher-end baffle filter link) http://www.filtersales.com/pdf/flame_gard_grease_filters.pdf

If you consider your ducting with its bends and higher loss due to being rectangular to be equivalent to 40 ft of 7-inch round duct, then at 300 cfm the loss might be around 0.4 inches, w.c. (This can be calculated using on-line calculation tools; I am just WAGing it here.)

The MUA is another source of pressure loss. Even a window screen can be significant, and a 3M furnace filter in line with an intake air duct will be higher yet for the same area. Usually, one needs blown MUA if the house pressure relative to the outside is to be kept close to zero. This is not needed for safety in this case.

So, whatever blower is selected for this application, it should be of the higher pressure class and overcome an inch or more static pressure loss at 300 cfm for a high probability of success at achieving 300 cfm.

Even if possible, enormous duct sizes are not optimal; choose ducting size to set the air velocity at the CFM achieved to at least 1000 ft/min (higher can be used in warm ducts).

kas