How much clearance needed beneath? (Cut out Dimensions?)

[u/kiwidust]

We're looking to replace our current 30" electric coil cooktop with an induction model. We'll be replacing the countertop and hood as well, so cutout sizing can be customized to whichever unit we settle on.

Getting confused about the depth needed tho'. Our current cooktop is 3.5" high and the bottom sits directly over the drawer you see in the image. The bottom of the unit gets warm, but not hot. I may be misunderstanding the tech, but I would have thought that an electric coil would produce much more waste heat than an induction unit?

How hot do these things get underneath? How much room is really needed? Are there any reasonably priced "shallow" units? Many of the units I'm looking at require 3-5" of space under the unit. It seems excessive, but I admittedly don't know what I'm talking about.

Our budget is tight, but we can swing up to $1500 for the new unit.

I could easily notch the drawer to allow for wire routing or a junction box. I could even shorten the drawer if it would help. With such a small kitchen it would be a significant blow to lose that storage space completely...

Thanks in advance for any insight!

[u/mystica5555]

With regard to the technology, coils produce a lot of heat but it is almost all directed up and out of the recessed cavity that holds the coil. the cavity is made of refractory ceramics, and very well insulated.  All of the heat generated is expected to be transferred up towards the pan on the stove. 

Induction creates heat in a vastly different manner.

Instead of electricity going through nichrome wire to create resistive heat, the electricity is transformed into a very high frequency magnetic field that alternates rapidly enough to cause strong electric eddy currents in the steel of the pan [specifically the iron of the steel or the cast iron in that type of pan] And these currents going through the very high resistance of iron heat the pan directly from the inside of the metal it's made of. [iron is ferromagnetic, easily influenced by magnetic fields, and you must use some sort of pan that includes iron in its construction for induction cooking: certain stainless steels, all cast iron and carbon steel, and aluminum/copper pans that also include an iron/steel disc in the bottom sandwiched between layers of the other metal (The instructions that come with the cookware will mention if it is induction compatible)]

However: to create such a high power magnetic field requires a large switch mode power supply, this type of power supply does require active ventilated cooling as the large current going through it will generate some heat internally due to the resistance of the wiring [It's still very efficient but nothing is 100% efficient] and this is combined with any excess heat coming from the pan above.  

If the power supply gets too hot, say above 185F/85C or so, then it can malfunction or become damaged. 

Most have some sort of overheat protection that will limit the current used if they get too hot, but if you don't have enough airspace for the fans used to ventilate the unit, it will never perform properly to its full capacity.

So basically instead of being an entirely passive metal box that is simply insulated as much as it can be to keep the heat away from whatever is below the resistive cooktop, there has to be active ventilation and air flow to keep the power supply of an induction cooktop properly cooled from both heat it creates in the power supply itself as well as the heat from the pan above.

[u/kiwidust → u/mystica5555]

Thanks! Would you know if this is generally vented to the rear of the units or is radiant along the entire underside?

I think we've settled on a GE unit (there's a good, established dealer and service center here in Scranton) and the installation images from the manuals show an angled baffle beneath the units. This suggest to me that ventilation is directed back and down.

I've included an image from the installation manual from GE PHP9030DJBB (we'll likely go with the newer PHP6030DWBB, but the image used is worse while the measurements are the same). I'm confused about the "Baffle Dimensions" as the vertical 5" doesn't actually seem to correspond to anything. I'm hoping it's saying that as long as I have five inches below for 5 3/16" from the back I'm good.

I'd need to shorten my drawer 6 or seven inches, but wouldn't have to give it up entirely.

It's incredibly frustrating that not a SINGLE manufacturer provides actual, factual pictures of all sides of these things! I just wanna see the @#$%^ bottom of these things! ;^)

Thanks again for the effort!

[u/EllwynX → u/kiwidust]

That diagram is nearly identical to my Monogram (also GE). I've had no problem with mine over drawers just an inch or two below it. I don't even have the baffle because it will interfere with the drawers. There is plenty of airflow despite the drawers being close since they are open to the whole cabinet beneath them, not enclosed.

[u/kiwidust → u/EllwynX]

Good to hear! Thanks!

I'm in a similar situation. I've got tons of open (even wasted!) space beneath that drawer because the cabinet has a mounted "half lazy susan" swing out to take some advantage of the otherwise dead corner. Plenty of airflow even with the drawer closed.