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

I just moved and thought my experience with my old house and the new house might help. Old house: Range: Thermador 36" with 4 burners; each rated at 15000 btu (I think); mostly do stir-fry; never had more than 2 burners on. Hood: 36"-wide; equipped with an internal blower, rated at 600 cfm; has 2 settings (low and high); the duct goes up, turns 90 degree, and travels between joists for about 18' to the exterior wall. My experience: The hood is used 80% on the "high" setting. It is noisy but acceptable. It gets the job done most of the time but falls short when I pan-fry steaks or fish - the house would be filled with smoke and smell oily. New house: Cooktops: I have two 15"-wide cooktops; one has a single gas burner rated at 18000 btu and the other is an induction (3.6 kw) with 2 elements. Hood: 36" wide with an external blower rated at 1300 cfm; has 3 setting; the duct goes up, turns 90 degree and goes immediately through an exterior wall. My experience: the hood is 90% on "low", 10% on "median" and never on "high" (aside from testing). When on "median", it's comparable to my old hood on "high" in terms of the noise level but do not have the smoke/smell issues like the old one. So overall, it's quieter and gets the job done. My suggestion: Go for the 1200!

I love the range Lizzie! We had and OTR microwave when we first installed the range. It would come on automatically every time I used a burner. I didn't even know it had a default to come on automatically (had been using it for 5 years), and EVERY time I turned on the range, the fan in the OTR started. We quickly decided that the OTR wasn't going to work and we had to get a hood. We actually have MORE room with the hood as it is only 10" deep (about 6" shorter than the microwave). But yes, we did have to get a counter microwave and put it in a corner. Are your cabinets already installed? I wanted an under COUNTER microwave, that hangs from the bottom of the cabinets and still leaves me a little bit of open counter space underneath, but they have to plug in inside the cabinet, and since we were retrofitting everything, we didn't have a plug in the cabinet.

Its going to take extensive carpentry, electrical, hvac, and a whole host of other skills to do anything the way it needs to be done here. That isn’t a simple project. At all. You might as well go whole hog as to spend 10K to just replace the range and vent. As in, find a better layout that doesn’t leave it hanging on at the end of a run. You’re gonna have to tear up enough stuff that you should look at total replacement. Of everything.