weissman: we've batted this around before. It's obviously an issue of what each of us considers acceptable, but it was our experience at the lake house with a 600 cfm VAH hood over a 5 burner PGM365 Dacor cooktop that pushed me to spec a 1200 cfm Fantech remote blower and a 64'' Modern Aire hood liner over the new Lacanche in our home kitchen renovation. If I sear hard over the 15,000 BTU burner on the Dacor (i.e. preheat pan for 5 minutes over maximum heat and then dump in meat or fish) I get smoke that temporarily overwhelms the VAH blower and spills into the kitchen. Since that's kind of how I like to cook, it was an issue for me. So, for me 600 cfm (or, per the VAH hype, "equivalent to 900 cfm with a conventional blower"--which I don't buy) was inadequate for even one burner when doing this kind of cooking. I'm hoping the 1200 cfm will be more effective (though now I have fan envy, as there is someone who has recently posted about his 2500 cfm blower--now there's a reason for makeup air!). yoyoma: Re the continuously variable speed control--it's an option I'd consider a must if you're spending this kind of money on a vent hood. Again, this is based on my experience with our VAH, which also has a 3-speed control. The main thing a continuously variable control gives me is the option to run at a very low cfm setting, say if I'm just cooking one pot of rice. The VAH is just so darn loud even at low that I wish I could run it slower. The sound issue is also obviously why I went with a remote attic-mounted fan and the Fantech LD10 silencer. The silencer is a popular option as I know of several installations where the LD10 was used even when the blower was from a different manufacturer. For example, one appliance dealer quoted me a Wolf hood system but with the Fantech silencer. Do beware of the good point paddy 99 makes. I know that I'm going to get significantly less than 1200 cfm given a 20' duct run and the silencer, as well as one 90 degree turn. I did consider going even higher but at least with Fantech blowers it would have necessitated going to an even larger duct size which I did not have the room to use. BTW, I assume you're aware that it's important to use the largest ducting possible, typically 10'' size. And, as for yoyoma's choice of the Independent liner--it is by all reports a very high quality unit. My only issues with it revolves around the limited number of blower options. Their website makes it sound like you have to use their blowers. That makes sense with an in-hood unit, but I'm not sure that's really true if you're using a remote blower, which I think is the superior option. My guess is that you could use other remote blowers without problems, which would allow you to 1) use a fan with a continuously variable speed control and 2) choose an attic-mounted fan rather than a roof-mounted unit, which is what I think the Independent CFMR1400 that they sell appears to be. Issues with roof mounts are: 1) difficulty in installing (particularly with a multistory house and/or a steeply pitched roof) 2) Potential risk of roof leaks once you punch through it with the ductwork 3) Wear and tear to the fan due to 24/7 exposure to the elements on the roof versus in a protected attic. Well, that's all I know about hoods. Hope it helps.

Joumir: I do not know what your friend may have meant meant by "pressurized gas" but you should ask him or her. I did hear the term used recently (once) to refer to propane (LP) which is stored in pressurized tanks.I heard this from a couple of out-of-state urbanites who bought themselves a trophy ranch here and needed to refill their propane tank. Most older stoves are set up for natural gas (NG).If you need to use LP, then your stove will need a different set of orifaces and burner components. I've seen numbers of these where old ranchers hung onto their old stoves (mainly Wedgewood and Merritt & O'Keefe models hereabouts) but they did their propane conversions decades ago.The difficulty of fnding LP components now varies from hard to impossible depending on age and model of stove. Easier to go from LP to NG rather than NG to LP because of the number of junked old stoves that can be cannibalized for parts. If you have an NG stove and want to run on propane,you need find the parts or hire somebody familiar with older stoves to make the conversion. So, if your friend was using the old Tappan with NG and you are running LP, do not, repeat, do not hook it up until you get the burners converted. One possibility that occurs to me is that that some really old stoves were set up to run on early NG systems which may have a different gas pressure than current systems. But we are talking stoves from before the mid-1930s. If your friend's Tappan stove was working in your friend's house when they bought it, and that was within the last, say, 50 years, it seems unlikely you would have that problem. Finally, if there is a mis-match between the size of the gas pipes in your house and the inlets on the stove, you will need to get adapters and might need to install a regulator. If you do not understand what I just said, you really want to hire somebody with experience with old stoves to check the stove out and handle the installation for you. (If it has been sitting for more than a couple of years, you should have the gas lines and burners inspected and maybe cleaned of any bugs or crud that may be in them.) This post was edited by JWVideo on Thu, Nov 29, 12 at 14:39

Thanks---yes, we have the same griddle setup as circuspeanut in the center, and do use it as a form of counter space, which is nice. So it's true that we're not completely giving it up until/unless we actually replace the range. And assuming we keep it, which we're leaning strongly towards right now, one of my summer projects is to rewire it so we can plug it in (right now it shorts out the kitchen!) I keep waiting for the rains to stop so I can take it outside and take it apart---usually May is safe, but this year there's still rain in the forecast, so I'm really glad we didn't decide to start the remodel a couple months earlier! We don't plan to have any uppers on the wall with the range, just hanging things behind it, so it isn't too much of an issue on that front. And while we could end the run with the stove, DH is not enthused about walking into the kitchen to have the stove immediately next to you, and we do like having counter to the right of it as right-handed cooks. However, we could definitely make this a freestanding piece vs. a built-in cabinet, which would get around the locking-in-the-size issue and have an added benefit of being a better workaround for one of the funky CA codes with access to gas lines than our current solution. I'd just want to be sure we had storage space in the piece, if so. I'll have to look around---we have a cheap Ikea butcher block there that does the job, but has really taken a beating in the three years we've had it. @farmhousebound and circuspeanut, I see you both have vent hoods that are (or look?) the same width as your stoves---do you find that a problem at all? Buehl's post reminded me that we still haven't figured that issue out. I'd been advised to get one 6" wider, but there seems to be a somewhat limited selection in 42" widths....maybe we don't really need that, especially as the O&M is only 34" anyway? Doesn't help with the dilemma at hand, but something else I'd been wondering! We're coming from no venting whatsoever, so it's hard to know where to start on that.

The necessary information may be found by searching this forum. To summarize: Obtain a hood that overlaps the cooktop by enough to capture the rising and expanding effluent. Assume for this discussion a hood with a 42-inch wide by 27-inch deep aperture area. This is shy of 8 square feet. Desirable velocity at the baffles is 3 ft/s, leading to a need for 24 cu ft/s or around 1400 cu. ft./min. Experience shows that only half this is needed due to baffle behavior in directing the effluent flow close to the baffles. (Or to look at it another way, only half the baffle space is aperture.) This consideration yields a value of 700 cfm. To actually flow 700 cfm, the blower needs to do so at some pressure drop determined by the baffle loss, transition loss, duct loss, and MUA replacement air flow pressure loss. For likely conditions, a 1200 cfm rated blower would be desirable. At best, a VAH hood's rated actual flow (600 in Homechef59's message) only avoids part of the pressure loss. It is not equivalent to a 900 CFM blower with a baffled hood except when each is hanging in air without a house and ducting. While a 1200 cfm rated system is recommended in this example, stepping down to 900 rated cfm may be adequate depending on what plume velocity your cooking effluent actually achieves, and what area of aperture you end up with. Some effluent escape (capture but missed containment) or effluent missing the aperture (missed capture) can be expected at some level of flow and/or hood shrinkage. Note that this basis for CFM estimation does not depend on the number of burners that may be in use at one time, but on the pan temperature(s). Every plume rises and has to be captured and contained, and the other hood areas not directly impacted by a particular plume do not help capture and contain it. kas