This topic comes up here from time to time. Amazing how many of those big-old units were sold by Jenn Air.

The usual suggestion for avoiding a countertop replacement/kitchen rebuild has been to fabricate an insert/overlay to adapt the old 46.5" cut-out to hold a current, smaller cooktop (or cooktops). Some suggestions have included making butcher block overlay (which will put the cooktop an inch or two higher and may pose ergonomic problems) or having a metal shop fabricate a stainless steel insert and frame that holds the new cooktop but covers the gaps. A stainless-steel frame probably won't be terrifically expensive if the existing counterop is not otherwise a problem.

Last fall, somebody here came up with an induction replacement that involved a long downdraft and a stainless insert that held a 4 burner 30" induction cooktop and a 2-burner induction cooktop, the combination of which filled the 46" cut-out for the old Jenn AIr. IIRC, they really wanted the extra long cooktop space but did not want to replace the countertops. Sorry, I can't find the thread at the moment.

>>>Can the existing countertop be trimmed to allow a 48 inch cooktop?<<<

Maybe. What is your present countertop made of? Laminate/formica? Stone? Tile? Butcherblock or wood? How much longer is the countertop than the base cabinet?

The bigger problem will be with the base-cabinet frame below. If you have a 48" wide base cabinet beneath that downdraft Jenn AIr, the interior space may not be wide enough to hold any of the 48" gas cooktops you are considering. Have you checked cooktop installation instructions to find out what is required for bottom clearances? If you have not already seen it, theinductionsite.com has a pretty good discussion of these kinds of issues at:

http://theinductionsite.com/replace-combos.shtml

>>>Can downdraft be used with gas? The cooktop is not against an exterior wall, and it may or may not be vented outside;<<<

It is possible. That does not make it a good idea. With a JennAir style of a cooktop level vent, it will just suck the flames away from the pots you are trying want to heat. Instead, look for a telescoping-type of downdraft (a/k/a "pop-up.") The higher the rise the better. I've seen some that rise up to put the intakes around 18" above the countertop/cooktop. Unfortunately, the higher the rise, the higher the cost.

As for running a 48" gas cooktop without exterior venting --- personally, I think that would be just plain nuts. Are you looking at those big gas cooktops for any reason other than it it is really hard to find anything else that could fill the space of the present old-Jenn Air?

Yes, I was just trying to look for something that would fill the space and in our vision for renovating the kitchen (whenever that happens), we did originally want gas, so that's why I was considering 48" gas cooktops. A 48" inch cooktop *would* prove highly useful to us, since we have a large family, but it's not an idea that I'm married to. And it's not like I'm going to have to force myself to downsize to a 5 burner induction cooktop; only 2 burners work on our big old Jenn-Air right now. If I want to make pasta *and* sauce, I have to use a tiny burner to boil the water, which takes a good 30 minutes or more. So anything is really an improvement.

We have laminate countertops that, frankly, need to be replaced. But since our cabinets also need to be replaced and we can't do that right now, we're just trying to make the right decision as far as timing goes.

If we do end up replacing the countertop, will we have problems installing a 36 inch cooktop in a 48 inch cabinet? #1 on my list for induction is the 36" Wolf. I think I would prefer frameless, but in another thread I read that it's harder to lift out that cooktop if we were to replace our cabinets later.

I'd love to know what the OP ended up doing. I'm in the same boat now.

Me, too/

Putting "@amgboord" into your comment will have a better chance of reaching the OP than just commenting into a resurrected old thread. Hovering over the OP's name above a comment will show additional information.

I have the same problem, We have granite counter tops. Hole cutout fits a 47 inch drop in downdraft. Jenn Air frame is stainless. It is 46 years old. Have had burners replaced and rewired. Purchased drip pans online and a cartridge from EBay. I think I smell burned wires sometimes. Sure have enjoyed having it. Grill was too messy. Looks brand new. Sit hot pots on the butcher block. Just the two of us now and getting too old to cook. A couple of burners won't work when you cut it lower than med heat. I don't want to spend the money to redo cabinets, and counter tops. We plan to stay home as long as we can. renovated the master bath to accommodate a wheelchair.