Glass top range teardown

I have been wanting to replace that old perlite/clay heat riser I've been using up until now which is getting me by, but it time for an upgrade. Looking through the classifieds, I found 2 free glass top ranges. Monday, I plan on picking them both up in hopes that they will provide me with enough ceramic fiber blanket to build a 5 minute riser and perhaps enough to replace some of the thicker rock wool around the combustion chamber too. I'll save the glass too in case one day I want to make a double shoebox rocket cooktop and/or cut it up and make a door or viewing window. We'll see how it goes!

Turned out one was unavailable but I did get the other one. Its kind of a nice unit and am looking to see if it can be repaired before tearing it apart.
As the name says on the top glass its "Schott" which is the real deal for high heat ceramic glass. Hopefully the ceramic fibre is on the inside too.
Looked up the price of a new glass top.... $475 ! Yikes.

The cook of the house did not want the range so I went ahead and started to tear it down. I haven't seen anywhere of this being documented so I thought I'd post a few pictures of what it looks like. Of course, all ranges are going to be slightly different but the general idea I think should be the same.

I removed as many screws as I could see until the top glass frame of the range was free to move up and down on its hinge (to change the elements if needed). With a utility knife, I cut all around the perimeter of the glass: Its some sort of silicone I think.
This did not free it entirely as on all four corners (from underneath) it is also secured with some kind of adhesive that needs to be cut also. It then popped right off.
The third photo shows what it looks like with lights shining through it: very opaque. The bottom of the glass has little dimples in it and is very brownish in colour which makes the visual look very dark and distorted.
To be continued.....

The teardown continues as the metal skin is removed. There was a combination of screws and tabs holding it together. Most cables were unplugged to access the back insulation. Not sure why there were different thicknesses of insulation - It wasn't that some were matted more that others.
The insulation was almost identical looking to the batt fiberglass insulation you use to insulate a house. Didn't experience any more itching or loose fibres to breathe in like the fiberglass stuff.
There were also what looked to be compressed vermiculite disks (with little fibres) under and around the heating elements. I didn't see any immediate use for them but could have potential if they were needed.
One really nice perk of the new riser is the diameter size reduction (to provide more room for gasses to flow more easily around the riser and down to the manifold) and the weight was considerably less. I could easily lift it with one hand! My perlite/clay riser I have to grunt with both hands to lift it.
The height difference between the two risers was only because I used a strip of sheet metal for the outer shell to hold the insulation that was 24" wide. No big deal as the heat riser for a batch box I'm told can be shorter. Besides, it is an experiment anyway!
On to the photos....

Sweet Deal Gerry !  
Your gona love that new riser!
Awaiting your post on how well it does!

Thanks for doing this and sharing it as well.
I didn't realize that these units used ceramic fiber insulation,  so cool!
It seem like one item could provide insulation, a top for  your bell(the glass)  and an oven, complete with a working, well fit door.

Well gents, its been an interesting experiment but just found a glitch in the matrix.... read on.  

This afternoon I fired up the beast and put a full load of wood in. Everything ran quite smooth without a hitch. A few hours later (with welding gloves on because I was impatient... I mean eager) I removed the barrel to inspect the heat riser. The outside skin was fairly clean and the top of the insulation was well intact. Then when I looked down the 'barrel' of the heat riser I was quite surprised. The 6" opening near the bottom had shrunk to about half that size and it looked like a marshmallow roasted over a fire. I took it off, laid it on its side and inspected the bottom. The pictures below say it all.

Long story short, I don't think this is ceramic fiber blanket, superwool or whatever else you would like to call it. It may be a high heat insulation suitable for oven temperatures but certainly not what will work for the extreme temperatures of a heat riser. Sigh!  😢

My original inspiration came from this thread: ceramic-fiber-build-discussion over at proboards mentioned by Matt Walker (the 6th post) then again on the last post on page 1.
I don't know if there was something I missed or perhaps every manufacturer uses a different insulation product, but whatever the deal, it wasn't meant to be this time around.
I think I will drop Matt an email and see if he could clarify things a bit.
All in all though, it was an experiment and this small setback certainly won't curb my rocket science explorations.

EDIT:  Well there's still the glass top to play with!
EDIT2: I just watched Matts video posted from the link above and in it he says at 28:50 that he's using the salvaged insulation from the range to cover the outside of the metal of the heat exchanger which of course would not be as hot as the inside of a heat riser. I could see it working there or perhaps even on the outside of a brick core as insulation.

Oh Man! Dang , hate it when that happens!
At least the old reliable riser was there to step up and keep getting the job done!
Might take longer than five minutes, but i'm sure you have a 5 minute riser in your future.

Great test Gerry !
Thanks for sharing this experience.

Just now added to my to do list is a massive batch box with everything as transparent as possible.
I think we could do the burn chamber,  door,  and bell at a minimum.
I have a local metal recycled that might be the place to intercepting glass top ranges.


I imagine building this rocket glass heater it in the center of a large gathering place.
It wouldn't  be very efficient, being rather low mass, but it would compare favorably to a bonfire, offering lots of radiant heat and warm light  without the smoke.

In a steam room or sweat lodge, the glass could be a great surface to flick water at/throw herbs on.

Imagine an windowless insulated  grow house,  warmed and illuminated by a  rocket glass heater and biogas lanterns.

The lack of mass is kind of a limitation, so perhaps this would be the place to choose water as thermal mass.
Normal silicon caulk is rated for way higher than 212°,  so the techniques used by DIY aquarium builders should work to build a boiling vessel.

Gerry Parent wrote:

Long story short, I don't think this is ceramic fiber blanket, superwool or whatever else you would like to call it. It may be a high heat insulation suitable for oven temperatures but certainly not what will work for the extreme temperatures of a heat riser. Sigh!  

This is such a good reminder of just how hot parts of a rocket stove can get and how important it is to inspect things carefully, and design things so they *can* be inspected carefully, particularly when you're experimenting! I've been gradually collecting the things I'll need to do an outdoor one for learning on, but I'm totally cool with learning from other's mistakes! Thanks for the great pictures, Gerry.

I heard back from Matt Walker. This is what he said in regards to the insulation:

"Hi Gerry,

 It looks like your stove manufacturer used a lower grade insulation. I'm not surprised that there are variations on the construction across different models, but it's the first I've heard of it.

You can find superwool online at Amazon for reasonable pricing. If you are unsure or not willing to experiment then that's likely a better source for you.

Warmly,

 Matt"

I then asked if it was OK to share his response and this is what he said:

"Hi Gerry,

 Sure, you are welcome to share my thoughts, thank you for asking. Thanks for your continued support as well, I greatly appreciate you and the gang over there and all the support over the years. Let me know if there's more I can do to help.

Warmly,

 Matt"

So the facts are:  1) Not all salvaged glass top ovens are the same so my findings may not reflect what you find

2. Matt is a super awesome guy!

I wonder if that also applies to the actual glass, obviously all glass hob tops can withstand hight heat but perhaps some are better quality than others?
I have had one for a few months but not actually fitted it yet......

Fox James wrote:I wonder if that also applies to the actual glass, obviously all glass hob tops can withstand hight heat but perhaps some are better quality than others?
I have had one for a few months but not actually fitted it yet......

Don't know the answer to that one yet Fox. Perhaps this summer I'll make something with it and post my results.
I'm wondering about the door glass too. There are 2 layers and don't know if the inside one is more heat tolerant than the outside one, the same or both not good enough for the high heat of a RMH.
I think though I'd like to test cut the door glass with my wet tile saw to get some practice before hacking into the top piece. Its nice to have a free piece to do this with as I think I'd be a lot more nervous if I spent a lot of money and have it crack on me.

I have been through a few pieces of glass, I get free off cuts from a local stove company, some last longer than others .
The glass is directly above my heat riser, I have only had one piece that actually cracked but most go opaque after around 10 hours or so.
I was given a hob top that I will try out soon, it is almost new without any scratches or obvious wear, my stove can show temperatures over 600c so it will be a good test!

Thanks for the tip on the off-cuts Fox. I think I read about the colour change over at Proboards. Should look that up again.
The glass top I salvaged from the range is so opaque that I don't know how much of the flame will be seen as in the DSR in allerton abbey: double-shoebox-rocket-cooktop or if it will get even more dark. Time will tell.

In the meantime, I just had an idea that since my batch box is still not cobbed in around the burn chamber, I could experiment with that door glass and make something that resembles Peters batch box thingy with the glass acting as the roof. I know it may not survive that kind of heat nor is it good to reduce the insulation and lower combustion temperatures but hey... lets see what happens!
Would I need to put a rope gasket down first then just loosely set the glass in place so that it has room to expand/contract without cracking? Any thoughts?

Hey Gerry,
Not a frequent poster here, but hopefully you can see past that. Please don’t cut that glass top! Often times tempered glass will shatter when being cut, but if it doesn’t using it in high heat could be seriously dangerous. The reason being: tempering glass adds a huge amount of surface stress all around the entire piece. This results in super strength properties compared to annealed glass, and the “safety feature” of catastrophically shattering into small bits (not shards) when broken. Cutting it unbalances that stress.

If you give it a try anyway, be prepared both while cutting or subjecting to heat for the piece to instantly shatter into 1/4” cubes.

Kind regards,
Mark

Hi Mark, do you think that only applies to ceramic cooker tops because the normal ceramic hight temperature glass can be cut quite easily with a standard hand held glass cutter.
I have never tried cutting a cooker top but, I have cut plenty of ceramic glass.

Thank you for the warning Mark. I am only going on what a few others have said from their experiences with cutting this kind of glass. I do plan on taking extra precaution just to be on the safe side though. Probably be a few more days before I have the opportunity to get to it though. Will be sure to keep you all updated on my success or failure.

The kind of glass that says "Schott" and "Ceran" in one of the upper corners is glass ceramic, certainly not tempered glass. I have cut one at Paul Wheaton's in 2017, in fact it is the one of the rocket cook top in Allerton Abbey. And I did some small clear pieces at home, also using a tile wet saw. Very important: support the glass with a piece of plywood or the like and cut it in two or three passes. I never tried to cut it with an ordinairy glass cutter, by the way.

Thank you for the tip and support Peter, both you and from the plywood  :)

I have watched a very experienced elderly gentleman cut replacement new glass to fit the individual windows in wood burning stoves.
He simply places the 300mm square panes of hight temperature glass over the selected replacement frame and cuts it free hand with a glass cutter.
I go to this fireplace company to collect whatever might be on interest to me from their rubbish skip, I usually get a few bits of glass left over from the 300mm panes, they have hundreds of the squares staked in the workshop.
I cut the piece in the picture with my cutter and even managed to round over the edges with a wet diamond stone.

My warning is based on knowledge of tempered glass in general and a single experience of an employee walking across a glass top range during a cabinet install. It shattered like tempered glass, but I have no info about how that particular glass was labeled.

Looks like “ceran” is not tempered, so...

Sorry for raising the warning unnecessarily!

Mark,  No worries mate! We are all here to learn and even to expand on what we think we know.

Excellent thread everyone. This is super interesting. following but wanted everyone to know this isnt just an echo chamber.

Over the past few days, I've been having this side conversation with Jay Angler and thought it may be helpful to post it.

Jay Angler wrote:If you're not going to use it right away, is there a reason you didn't remove it at the hinges so it stayed in its metal frame for safer/easier storage? (I'm just curious what your thinking is?)

That's a great point Jay! It was kind of get-er-done kind of project and things were getting sliced and diced very quickly. As an afterthought, I ended up keeping the frame the glass mounts to because if I make the cooktop as large as the original then the frame makes an awesome flat mounting point and cob in the rest to the body of the stove.
So I might have to reattach it if that is the case! But thinking out loud, it also might be good to be able to lift the glass out to be able to clean under it. So much to find out!

Jay Angler wrote:Being able to lift it to clean under it sounds like a good plan to me. Hubby has some sort of heat-tolerant silicon goop that he's used on our wood stove - would a small bead of that to seal and support but not "glue" in do that? I will keep watching this thread to see where you go with this!
That said - the ultimate question is: if someone dramatically boils over a pot, where will the mess end up?

If the glass is going to be removable, I'm thinking something more like a rope gasket but it may be kind of thick and elevate the glass too high up out of the frame.
If I silicone the glass back onto the frame permanently and instead make the frame separate from the body of the stove, that could work also.
Both options I won't know until I get to that point.
Looking at the design of the cooktop in Allerton Abbey, it looks like there is a rounded wall around the entire perimeter of the glass top. I'm assuming a boil over would then stay contained like a swimming pool. It would not be good to have liquids dripping onto the hot bricks inside the stove which could crack from the thermal shock.
If the glass was made removable without a silicone seal, this could happen. Always a catch to consider isn't there? This is why its very helpful to discuss all these things that only one person may not catch and have more redo's that could have been prevented.

Gerry Parent wrote:

Looking at the design of the cooktop in Allerton Abbey, it looks like there is a rounded wall around the entire perimeter of the glass top. I'm assuming a boil over would then stay contained like a swimming pool. It would not be good to have liquids dripping onto the hot bricks inside the stove which could crack from the thermal shock.
If the glass was made removable without a silicone seal, this could happen. Always a catch to consider isn't there?

True story time: Years ago we bought a glass-topped convection oven from a reputable brand. I specifically wanted the element dials on the front like a gas stove so I don't have to reach over hot pots to turn them off. The only one we found that fit the bill had the new electronic system for oven control, and this was also mounted on the front. It had a lock on it, and no small kids here, so I figured I could live with that (the element knobs just pull off to make it safe for young children). We were asked to host a couple of Japanese school girls for a week, and they were instructed by their teachers to "cook us a Japanese meal". They managed to boil over the pasta, and the manufacturer had failed to put a proper seal between the front of the glass and the front of the stove, so the pasta water dribble down all over the electronic module. Luckily, hubby is a consummate fixer and electronics engineer, so he took the front of the stove apart, cleaned the electronics as best possible, and got things working. I insisted we call the company because there's no way I was going to put up with a stove-top that couldn't tolerated spills! Now that some sort of gasket has been installed, we've not had any more problems and the stove is now about 10 years old.
The moral of the story is: cooking messes will occur, so you might want to plan from the outset where the mess will land, and how it will get cleaned up!

Jay,  I remember at our cottage we had propane grill which at the back middle was an oblong drain hole where all the bacon grease or whatever 'shlop' you wanted to get rid of got pushed to which then was channelled into a pan below for removal. All the sides were slightly raised so it was kind of like a really shallow tub where things had to go down the drain instead of over the sides. Perhaps something like this could be incorporated into the design?

Gerry Parent wrote:Jay,  I remember at our cottage we had propane grill which at the back middle was an oblong drain hole where all the bacon grease or whatever 'shlop' you wanted to get rid of got pushed to which then was channeled into a pan below for removal. All the sides were slightly raised so it was kind of like a really shallow tub where things had to go down the drain instead of over the sides. Perhaps something like this could be incorporated into the design?

Yes, I can picture something like that. You'd have to push it to the hole or else have the cook top on a very slight slope which is not ideal if cooking things like omelet in a fry pan, but would be fine for many other dishes, so again, decisions and compromises!

My experience with the glass cook top is that if it boils over it boils off and cooks onto the glass. With the whole top hot on a rocket cook stove that should be even more so.  Keep a spatula handy to scrape up spils before they get too hard.

Hi Hans,  Thanks for the direct experience. Do you happen to have a picture to share? I am in the dreaming stage of building one and it would be nice to see others creations for inspiration.

Thought I'd give the stove salvage operation another try. This time with a damaged glass top Frigidaire range. Learning from the first attempt with the Maytag range, removal of two screws allowed the top to pivot upwards to expose under the glass top to the insulation below. The insulation looked exactly the same as in the Maytag, so my confidence that it was any different was minimal, but I just wanted to be sure. I hit it with a propane torch for about 11 seconds and it melted about an inch down. See video below. Certainly not worth any more of my time to dismantle it any further.

So with these two tests under my belt, I think if I was to ever look for ceramic fibre blanket again in a glass top range, I would bring a screwdriver and torch with me and test it on the spot before loading it up and hauling it away.

As far as the top glass, since it was already broken, I took one of the shards and cut it with a wet tile saw. Since my saw has a fixed blade there was no way to make several passes to cut, so it was all or nothing. It cut about as easily as a clay tile of the same thickness. No drama whatsoever.
If you look at the picture, there is some very minor chipping along the cut edges (cut from both directions) with only a few bigger chips (maybe 3mm). Easily concealed with cob, high heat silicone, a metal edge, or whatever.
 
I would like to test these cut shards for heat resistance in a few places (at the base and top edge of the heat riser).
Stay tuned for the outcome...

So now you've got "stuff" from two dead stoves. How about we start a stove version thread of what creative things can we do with the corpses?
https://permies.com/t/135617/permaculture-upcycling/ungarbage/Creative-ideas-parts-broken-washers

Ideas for how to test just how fire-resistant the glass is would be great.

The insulation isn't good enough for inside a RMH, but are there other places where it would cope? For example, we have a collapsible metal camping oven. I had hoped to be able to use it on top of our regular wood stove (Pacific Energy) but it looses too much heat through its top and sides to actually be useful in that location. I've always wondered if there would be some way to insulate it enough to actually work?

Convection stoves have fans in them and ours is quite quiet, but I don't know if that's just because it doesn't actually move all that much air. That said, there might be a place for "just a little air flow".

This is another situation where all the "junk" that wouldn't be junk if it weren't so hard and expensive to repair them and if people learned the skills as a matter of course, rather than it just be the 1% who can't stand to see waste who learn how to repair it. Re-use isn't quite as good, but it's still a big improvement over the landfill.

Jay Angler wrote:So now you've got "stuff" from two dead stoves. How about we start a stove version thread of what creative things can we do with the corpses?
https://permies.com/t/135617/permaculture-upcycling/ungarbage/Creative-ideas-parts-broken-washers

Actually, the first one has had all its parts distributed around. The insulation for a future wall cavity, some of the metal kept for future projects and the rest of the metal (90% of the stove) off to a metal scrapyard where the local fellow gets a small income from it being sold to a recycler. The second one as I mentioned, has only been partially taken apart, but I will cruise over to your thread and see if something else can be repurposed from the metal heap in the shop.

Jay Angler wrote:The insulation isn't good enough for inside a RMH, but are there other places where it would cope? For example, we have a collapsible metal camping oven. I had hoped to be able to use it on top of our regular wood stove (Pacific Energy) but it looses too much heat through its top and sides to actually be useful in that location. I've always wondered if there would be some way to insulate it enough to actually work?

The insulation may not even be able to handle the heat from your wood stove. Even if it could, I would probably recommend not putting it there as it may cause the metal to warp from overheating. Clay bricks or rock has been used by many people as a way to capture and hold some of that heat around a conventional wood stove.

Jay Angler wrote:This is another situation where all the "junk" that wouldn't be junk if it weren't so hard and expensive to repair them and if people learned the skills as a matter of course, rather than it just be the 1% who can't stand to see waste who learn how to repair it. Re-use isn't quite as good, but it's still a big improvement over the landfill.

I know I gasped at the price of a replacement ceramic glass top. No wonder why the people who owned the second stove with the busted glass top gave it away. The first one had a control board that was faulty and also cost about 1/2 the price of a new stove.
Along with the stove, I found a front loading washing machine that I repaired by bending a metal contact just a wee bit in order for it to complete a circuit so it would go into high speed spin. Nice to have a back up anyway out in the boonies.  

This evening I pulled out the glass shards from the batch box. One right next to the port, one was right in the firebox, one at the base of the heat riser and the last one at the top of the heat riser. All 4 of them looked exactly the same with no signs of degradation. Nice to have a success after the insulation bust.
With this confidence, I'm going to definitely move ahead with the cooktop this summer.

No idea yet whether the door glass has the same high heat properties. Another time....

It makes me wonder if perhaps this same glass could also be used as a protective liner for a RMH core? (to protect ceramic fiber, light weight insulated fire brick, perlite clay cast core etc.) It takes up a lot less room than hard firebrick and wouldn't suck up as much heat from the fire to get to the high clean burning temperatures much quicker. Also, another experiment at another time.....

Possibly then the glass could be used as a firebox liner in the air crete rocket mass heater.

Then the metal from the stove used as the surround for the air crete stove body and the air crete mass around the heat riser..

Thanks for the suggestion Hans. I've 0 experience with aircrete but is on my to do list of things to try.

As another note for the Frigidaire range, the glass top is going to be a little more tricky to remove as the metal frame its mounted to goes from one side to the other with only holes cut out for the burners. This means that one can't get a knife between the metal frame and the glass from underneath. The silicone is at least 1/8" on the horizontal plane so the glass definitely can't just be ripped off as the silicone really holds well.
Just goes to show you that every model will be different. Some being easier to disassemble than others.

EDIT: At first I tried cutting the metal with a cutoff wheel (top right of photo), but it was taking way too long since I was being careful not to hit the glass just millimeters below. Instead, by taking off the elements and using the holes they were in, I was able to get a utility knife with the blade extended all the way out to reach and sever 95% of the silicone seal - the rest was carefully sliced from the top at an angle.

One thing I noticed about how the glass is attached to the metal frame. Right along the edges (4 corners, top and bottom middle), there were 6 small square double sided adhesive tabs that were about 1/16" thick. I think these are put in place first to not only temporarily hold the glass in place but more importantly, to raise the glass up off the metal. I figure as the metal expands and contracts differently than the glass, these tabs prevent any cracking from happening. The silicone is probably then added around the edges to seal the whole thing from water infiltration below.  

A test I performed from the tear down I posted on a different thread:

Front door glass test:

J tube-Batch-Box-Conversion

I just replaced my glass top stove for $600.00 & you said the top replacement is $475?! WOW.