Well, "any" is potentially a very small amount, and I'm sure that there is some slight amount. My attic, however, is vented all around the periphery, at the ridge, and also with an attic fan housing. Ice dams at the roof edges tend to occur when the outside air warms up during the day and heats the snow bottom up through the vents instead of top down. In my present half-completed configuration, the ~ 2 x 2 ft heat exchanger sits above a Cooley and Hart 3 x 3 diffuser in a hall ceiling. There is a furnace filter taped down on top of the heat exchanger. This style of filter (Honeywell Filtrete) needs significant pressure drop to move much air through it, and I was pleased to observe that warm air doesn't seem to rise through it in the winter, or hot attic air settle through it in the summer. The sides of the heat exchanger and its plumbing are buried in insulation. When kitchen fans are running and the house is closed up, air is pulled through and the thermostats, the larger-than-typical-size Taco pump, and the furnace controls do their thing to heat the air. (The circuit is capable of well over 100k BTU/hr depending on furnace and air temperature.) The problem, as I have pointed out a few times here, is that pulling air through a filter and heat exchanger requires a pressure drop -- a drop too large for combustion appliance safety. My only combustion appliance is an oil furnace, and it now uses its own MUA system to avoid back-drafting. Nevertheless, if I were to run both kitchen fans at once at full power expecting all flow to be made up through the heat exchanger without fan boost (possibly 1400 actual cfm with restricted MUA), the pressure drop in the house causes some furnace exhaust to be pulled into the house via tiny cracks not normally relevant when there is a positive draft, so I don't do dat without an opened window. My intention is to duct the heat exchanger to a mushroom air intake already installed on my roof via an axial in-line fan and a four-inch pleated filter caddy so that at the maximum possible flow rate (possibly 2000 cfm, say) the house pressure can be balanced and all the MUA comes from outside without mingling with the attic air. A damper may be needed, although as noted, the Filtrete coating will be pretty resistant to air passage without some deliberate pressure drop from the in-line fan. kas

Replacing the existing duct work is a big deal. As I said before, there are 600 CFM hoods that work with 6" ducting - that would be your best and least expensive option at this point. Is it a perfect solution - no - but it is a reasonable solution. I was in a similar situation - I have a 600 CFM hood with a 6" duct over my DCS 30" gas range. It is quite powerful enough - the only drawback is that it is only 19" deep so some stuff escapes the front of the hood. I occasionally have to clean some grease off the front of the hood. Not a big deal.

I got a private label re-branded Zephyr Typhoon from Signature Hardware on clearance for $350 in black. I know it is the exact same as the typhoon because the interior schematic maps are identical. Their website has it spec'd as 600 cfm but I do not believe this; I believe this is the full blown 850 cfm typhoon. I love this hood and it was a great price, see how strong it is, that is a full size corningware french white quiche pan it is holding up (basically like a pyrex pie pan - and note that in this picture the second fan is wide open during this)!! But do beware this hood is a BEAR to install due to finicky mounting hole locations, and you would need at least two adults if you do it yourself and don't want to be frustrated. Also, on the "slanted" underside: this is engineered into the hood so the draft is more efficient at pulling the fumes/steam/heat that you want up into the fan. If the surface were only straight down, then some of the fumes/steam/heat would escape up the front surface outside the hood. That angle provides a small CROSS angle current so it is sucking up from directly below and also a small proportion from frontward, so more is captured. A hood is first a functional piece of equipment and secondarily a cosmetic consideration! Here is a link that might be useful: My hood, powder coated 16 gauge stainless This post was edited by beautybutdebtfree on Fri, Feb 28, 14 at 8:43

I'm not that helpful. But I do love my 42" kobe 1100cfm range, over my 36" Miele induction cooktop. -- What were/are your priorities in choosing? What makes for better capture and lower noise? Width/depth? Duct size? Single/dual blower? Priorities: 1. cost 2. as much CFM as I could afford - I cook with a lot of "fragrant" food (onion, garlic, fish, curry, bacon, etc), so I needed all that smell out of my house - and the power to suck up all the grease and steam (hardly any smoke, since we don't have a grill). 3. baffle (so easy to clean) 4. 42" size Duct size/# of blowers are determined by the design and power of the hood. good luck, Amanda