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I want to install an induction cooktop (GE model PHP9036DTBB) into my granite countertop, but looking through the installation manual, I have a few questions.

  1. In picture 1 below, why does the junction box need to be installed a minimum of 16 inches away from the top of the countertop? The diagram also suggests it needs to be a junction box situated outside the wall, but would an in-wall junction box work? Would an in-wall box allow me to use a shorter distance between it and the bottom of the cooktop? The middle of my current electrical box (which is where the manual appears to be measuring from) is located about 12 inches below the surface of the countertop. Would that be sufficient?enter image description here

  2. In picture 2 below, the installation manual seems to require 2 inches of clearance between the edge of the cutout and any wall beneath the counter. The cooktop I'm replacing, which is gas, has less than 1 inch of distance in this regard, if I'm understanding the manual correctly in what it's measuring. (For what it's worth, it appears the previous owner of my house improperly installed the gas cooktop in this way, since the manual for it says there should be 3.75 inches for this same thing.) Why would the induction need so much space in this respect?enter image description here

Any help understanding this is appreciated!

Andrew
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  • Does the cooktop fint in the cutout in the granite and is it supported by the granite on all four sides? What is the distance between the inside surfaces of the two walls? 30""? A lot of people would just install the cooktop if it fits in the hole. A hack that might lower risk would be to line the inside walls with metal sheeting. The current location for the junction box (12" down) should be fine if you can reach it from the cabinet below. – Jim Stewart Nov 30 '23 at 17:09
  • I can easily reach the junction box in the cabinet below (after popping out a drawer, which sits about 6 inches below the bottom of the current gas cooktop). And I haven't fit the induction into the hole yet (the measurements for the cutout fit within GE's requirements, so it should rest on all four side). But the current gas stove has an under-countertop clearance of 1 inch from any wall on the right side and in the front; the back has 3 inches of clearance; and the left side has a 0.5 inch clearance. And the distance between the left and right walls under the countertop is 35 inches. – Andrew Nov 30 '23 at 17:15
  • The instructions should state the volume of the space below the cooktop required to allow mixing of the hot air expelled from the cooling ports under or at the side of the cooktop. Conceivably you might have to replace the drawer with just a cover, perhaps with vents to allow mixing in the entire cabinet volume. Instructions should state clearance required underneath. – Jim Stewart Nov 30 '23 at 17:21
  • The instructions just say 3 inches of clearance from the bottom of the cooktop to any combustible materials. I should have at least 5 inches of clearance from the bottom of the induction to the drawer that's under the cooktop. – Andrew Nov 30 '23 at 17:23
  • Perhaps there is enough space on the sides and back of the drawer to allow air exchange with the cabinet below.. Are the tops of the sides of the drawer wood? Are they closer to the bottom of the cooktop than 3"? I think the instructions don't suggest have a drawer there, but it would probably be OK. You might have to curl thin metal over the sides of the drawer. Do you use it as a drawer or is it empty? – Jim Stewart Nov 30 '23 at 17:27
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    The sides of the drawer are wood, but they should be 5 inches (or more) from the bottom of the cooktop, so there should be plenty of clearance. We do use the drawer. – Andrew Nov 30 '23 at 17:42

1 Answers1

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I think there are two very different issues here:

Heat

Clearance on sides, back and above are likely based on heat. An induction cooktop can produce a lot of heat. While most of that heat is on top and directed upwards, the rest of the appliance can get hot in use, which is likely the reason for the 2" side clearance. If you don't follow the directions and you ever have a fire, you could find insurance not wanting to pay for damages. Really.

Wiring

Many ovens and cooktops come with an integral junction box. You connect your own wire whip or NM cable or whatever (specs and options vary) to the oven or cooktop and to a junction box.

However, this cooktop comes with an integral 4' conduit. My hunch is that they are seriously concerned about people hooking up too-small cables or trying to set it up as a plug-in/receptacle, both of which can lead to serious problems with an induction cooktop that needs a 50A circuit! A lot of older electric cooktops (and some current models too) use a 20A or 30A circuit. Or even worse, a 40A circuit (more common for a full range = cooktop + oven, than just a cooktop) with a NEMA 14-50 plug/receptacle (so 40A circuit but 50A receptacle which can fool some people into thinking they have a 50A circuit when they don't). In addition to other issues, the larger receptacles tend to have more issues with overheating. So really for almost anything larger than 30A, hardwired is the way to go.

Your average cheap appliance installer (delivery and installation included free on all orders over $x...) will slap a standard plug/cord on an appliance to match the appliance and the existing receptacle. They will not deal with hardwiring - they know that requires an electrician. So they will not attempt to install this thing for you.

Which means that you end up either doing the research (as you are now...) to DIY, or call an electrician. Either way the end result is likely to be:

  • Check existing circuit. Breaker 20A or 30A or 40A. Wires not large enough for 50A.
  • Run new 50A circuit with 6 AWG copper cable, 8 AWG copper wires/conduit or 8 AWG aluminum wires/conduit.
  • Install an appropriate junction box. Which may need to be larger than the previous junction box due to larger wire size.

In order to enforce that, the manufacturer includes a 4' conduit with wires. That way you are far less likely to cheat - doing so would clearly void the warranty. But there is a problem - wire bend radius. 16" is 1/3 of 4'. So with that 16" minimum basically the conduit forms a big loop. With 12" you are more likely to end up with some sharp twists and turns - which is not a good thing.

manassehkatz-Moving 2 Codidact
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  • Thanks—this is helpful! Re: wiring, the current junction box is set up to be a hardwired, not to use a plug. It's also on a 50 amp circuit. Re: heat, would cutting out the wood walls to the left and right of the underside of the cooktop be sufficient disperse that heat? On the other side of each wall is just more under-cabinet space, and the walls don't appear to be load-bearing, as there's a tiny gap between them and the granite countertop. If that's not a good enough fix, any suggestion what to do here? – Andrew Nov 30 '23 at 18:15
  • Don't be so quick to say "not load bearing". Granite is heavy stuff and the installation may have been based on "cabinets every 'x' feet minimum". Hard to say. – manassehkatz-Moving 2 Codidact Nov 30 '23 at 18:16
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    @manassehkatz do you think he could get away with removing the drawer entirely and putting a grill over or into the drawer opening? Then a grilled port in one or both of the cabinet doors. This would provide circulation of hot air out the drawer opening and cool air into the cabinet below. Then sheet metal over the insides of the walls close to the sides of the cooktop. Only real solution would be to return this (36" ?) cooktop and use a 30" induction cooktop. Construct an insert that would fit a 30" cooktop. – Jim Stewart Nov 30 '23 at 18:54
  • Could he cut out the tops of the cabinet walls and insert custom made load bearing steel inserts that would support the granite? – Jim Stewart Nov 30 '23 at 19:03
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    @JimStewart All of that sounds possible/plausible. But unfortunately we don't know the real engineering constraints. Is it air flow? Is it literally the surface of the sides gets hot? etc. A GE engineer could tell you - but getting through the bureaucracy of GE to get all the way to someone who actually designs the stuff is probably nearly impossible. – manassehkatz-Moving 2 Codidact Nov 30 '23 at 19:03
  • Get a custon made, slip-in metal frame to fit a good quality 30" induction cooktop. – Jim Stewart Nov 30 '23 at 19:08
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    Just got a remodeler to our house, and we confirmed that the countertop isn't resting on the walls to the left and right of the underside of the cooktop (you can pass a piece of cardboard between the top of each wall and the countertop, all the way from front to back), so we're cutting out the necessary room to disperse the heat on the sides of the cooktop. The countertop is supported entirely by the back wall and the front wall of the cabinetry, neither of which will be touched. – Andrew Nov 30 '23 at 19:15
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    When I said a steel insert I meant not just a plate but an open rectangular cross section duct that would mean there is no wooden wall there or any wall. If there is no support between the cabinets and someone would later set something heavy there it could crack the granite. Maybe this is overkill. Could be added later from the other cabinets. Could just use linear angle steel inside the two flanking cabinets. – Jim Stewart Nov 30 '23 at 19:21
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    Honestly, this is probably overkill. If it's anything like ours, there are simply fans that blow hot air down from the bottom of the cooktop. The air inside the cabinet does get warm, but it's not *hot*. We just store pots and pans in the cabinet below. I'm assuming your cabinet is at least a 42"? – Huesmann Dec 01 '23 at 14:56