How would you describe update: $5k spent? $20k spent? $100k spent? How tolerant are you of grease and odor spreading through the house, condensing on walls and fabrics? Do you ever cook at temperatures that cause vaporization of oil and/or grease, such as wok cooking or meat searing?

In general, to assure full capture of rising and expanding cooking plumes, one needs an overhead hood with an entry aperture that extends beyond the edges of possible pans used on hobs by the amount of expansion at the height of the hood above the cooktop. Induction cooking does not relieve one of this necessity, it only relieves one of the extra plume components from gas combustion that rise with the cooking plume.

Further, the actual airflow rate must be sufficient to achieve containment of the captured plumes before they can reflect out of the hood. (See a bazillion threads here on this topic.)

Downdraft collectors and pop-up side-draft collectors can only handle very low velocity cooking plumes such as from poaching or other water based light cooking, and maybe low simmering of such as bacon. Otherwise, the momentum of the cooking plumes is too high to redirect them sideways or force a U-turn. (See dozens of threads here commenting on this.)

Ignoring all this, whether another down-draft or side-draft assembly can connect to the existing ducting depends on details within your cabinetry. Whether a modern pop-up side-draft unit can work, even ineffectively, with whatever duct size you have would be a question that the installation directions for representative units might answer. Broan and Wolf make such devices, as I recall, as well as others.

@HU-22921295

Do you have model numbers for the Thermador cooktop and (presumably) Thermador pop-up?

Also, when you say that the"switches to move up/down and start fan are integrated with the existing cooktop switches" do you mean that there is an actual switch panel that is part of the cooktop or do you mean that that the pop-up just rises and lowers automatically when you turn a burner (or burners) on and off? I'm guessing that you did not receive a copy of the user guide or installation manual for the pop-up when you closed on your new house, right?

I'm asking because of my experience (a few years ago) of helping friends who had just bought a house that came with a Thermador pop-up behind a stove or cooktop. (Been a few years so can't recall now which type of appliance it was.) Because my friends didn't receive the user's guide for the pop-up and because the unit was already set to automatic mode, they thought that the pop-up was integrated with with the existing Thermador stove or cooktop simply because it rose and lowered when the burners were turned on and off.

Anyway, my "help" was finding them the user guide and installation manual and pointing them to the touch controls, one of which allowed the unit to be switched between auto-on and manual operations.

As I said, it has been a few years, but, IIRC, the auto-on feature operated from some kind of heat sensor that did not require being wired into (or "integrated with") the cooktop.

Also, IIRC, there was a physical button on the upper right hand top corner of the pop-up. Pressing the button would manually raise or lower the pop-up. When raised, the pop-up had a small touch panel display on the face of the right hand edge of the vent. IIRC, the middle button/lighted spot was what you pressed to activate and de-actvate the auto-on feature.

So, that Thermador pop-up, at least, could have been used with other brands or types of cooktop. Dunno if its is the same for your unit but I'm suggesting this in case it is.

FWIW, my friends soon decided to replace the pop-up with an overhead vent for all the reasons listed in Kas's post.

This is a Thermador GAS cooktop with a downdraft range hood whose up/down and fan switches are on the cooktop. If the hood is actually separate from the cooktop, perhaps you can disconnect the up/down- and fan- switch wires from the cooktop, connect those wires to switches you buy at Home Depot or Amazon*, and replace the old cooktop with a new induction one. Of course, the big questions will be whether you'll be able to find a cooktop that will fit in the space the old one occupied AND that can be installed adjacent to the old hood.

*Of course, you'll also have to find a place to mount the now-separate old up/down and fan switches.

Thanks everyone -

@kaseki - given the location of our cooktop, we would have to go ductless on an overhead range. Any opinions on that? We are going to update cabinets, and there is one potential layout where we could move cooktop to get an overhead duct to a hood - but it we are concerned it could crowd the entry way of kitchen, so it's not most ideal.

@jwvideo - I believe the model number for the Thermador pop-up is CV 2236 - but a quick search on Thermador website isn't a total match. I will poke around a little more to see what I can find - thanks for the suggestion. And yes, I mean that there is an actual switch panel part of the cooktop - nothing on the side.

@wdccruise - video is super helpful, that looks very much like our configuration (think it's #1). We would need new switches and somehow connect them to existing downdraft and yeah, it's unclear how things may ultimately fit.

An "up-draft" (hood) is always preferable to trying to collect from the side or down. Go for a route to the outside if at all possible.

For recirculating (ductless), the only model well described here is the VaH ARS. See https://www.houzz.com/discussions/2347276/vent-a-hood-ductless-ars-range-hood-update#n=65. Note that unlike these thin under cabinet ductless hoods with some stab at a filtering system, the VaH ARS has a filter pack above the hood in a duct style assembly.

I believe Broan/NuTone/Best also have filtering recirculating hoods that should be evaluated for whatever flow and overlap options there are. I haven't evaluated these or searched out other manufacturers.

The disadvantage of even the best recirculating units is less than desirable flow under heavy duty cooking conditions (commercial recirculating is likely an exception). The advantage is no make-up air is needed to keep house pressure close to the outside pressure. Window ventilation is desirable for dilution of any gasses that get through the filtering.

A brief search on the CV2136/2236 cooktop turned up some parts diagrams and a service manual.

Here is a link I found to Thermador's parts diagram and parts list for the electric cooktop and its ventilators: https://www.thermador.com/us/supportdetail/product/CV2236/01#/Tabs=section-spareparts/ (The difference between the ventilator models seems to be only in whether the blower is mounted with the pop-up assembly or mounted remotely. That won't affect your ability to re-use the existing system if you choose to do so.)

Here is a link I found to what seems to be the service manual (including a wiring diagram) for this line of ventilators: http://www.uncleharrywizard.com/nephewclub/wizardrange/bosch/thermadore-cook-n-vent--.pdf

These show that, as wdccruise suggested, the ventilator's wires and etc. can be dismounted from the CV2136 electric cooktop. You can even re-use the control knobs and switches. That coil-burner cooktop is old enough that it lacks microprocessor driven integrated circuit boards which makes it easy to dismount the knobs and switches from the old electric cooktop, remount them in a fabricated box someplace, and re-use the pop-up ventilator, if that is what you choose to do when you remodel with a new induction cooktop in a presumably new countertop.

Oh, if the ventilator does not already have its own 120v circuit to power it, you'll need to have one added because new induction cooktops won't have a takeoff for 120v accessories.

The NEC allows pull offs of 120 Vac circuits from stove 240 Vac power for peripheral devices such as clocks. I think a ventilation blower would be outside the intended scope of this allowance, but I would want to re-read the exact language before arguing one way or the other. (I wouldn't do it myself unless faced with a near impossible wiring job.) Always best to have the blower powered via a separate cable and breaker.

In addition, you may have to upgrade the wiring anyway; my 36-inch Frigidaire Gallery requires 50A wiring and breaker. The induction cooktop you select may have greater power needs than the existing cooktop.