Author Topic: Infrared broiler burner in gas pizza grill -What's wrong with my design?  (Read 4982 times)

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Offline creaton

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I'm seeking input on how to make a top-fired ceramic infrared broiler burner work in the gas grill mod that I've put together.

My design idea was inspired by jgame's http://www.pizzamaking.com/forum/index.php/topic,10241.20.html top fired infrared burner grill mod, the rotisserie rotating pizza stone from Tampa http://www.pizzamaking.com/forum/index.php/topic,10241.0.html, and the insulated stainless steel top from robis http://www.pizzamaking.com/forum/index.php/topic,7333.0.html.  After months of collecting parts I finally put something together (see pix). The problem is that the infrared burner does not work well.  It works great with the top off, but with top on it only stay lit for about 15 seconds before going out.  My sense is that I'm suffocating the infrared burner because of an air-flow issue.  I have no vents for air to enter/exhaust the unit other than the rectangular slot where the pizza goes in.

So I'm seeking input on how to modify my build so the IR burner will work. Should I build a chimney/vent? If so how big and where to put it?  Any and all suggestions would be greatly appreciated.


Offline pizzaneer

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you should be getting enough entry air from the bottom and from the slot- what you need is somewhere for the oxygen-depleted hot air to go. otherwise it's like putting an upside down cup on a candle.  maybe a chimney?  something with an adjustable flue.


 Nice clean work!
I'd rather eat one good meal a day than 3 squares of garbage.

Offline creaton

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you should be getting enough entry air from the bottom and from the slot- what you need is somewhere for the oxygen-depleted hot air to go. otherwise it's like putting an upside down cup on a candle.  maybe a chimney?  something with an adjustable flue.


 Nice clean work!

Thanks Pizzaneer!

Any ideas where the best place would be to put a chimney?

Offline pizzaneer

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In the front, about 2" back from the wall. This mimics the classic WFO chimney.  I can't really enumerate specific reasons why it should work, I just think it will (OH NO THE RIGHT BRAIN IS TAKIN OVER!!) and will look purty too.
I'd rather eat one good meal a day than 3 squares of garbage.

Offline shuboyje

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Without a vent at the top of the chamber I think you might continue to have the same issue.  The hot smoke will rise to the top and choke the burners supply of oxygen.  To maintain your current configuration you would need a burner with it's own supply of fresh air from outside the chamber.
-Jeff

Offline pizzaneer

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yeah, maybe I wasn't too clear:  chimney pointing up, located on the top surface, about 2" back from the front wall...
I'd rather eat one good meal a day than 3 squares of garbage.

Offline creaton

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Without a vent at the top of the chamber I think you might continue to have the same issue.  The hot smoke will rise to the top and choke the burners supply of oxygen.  To maintain your current configuration you would need a burner with it's own supply of fresh air from outside the chamber.

Seems that the top vent/chimney may be the easiest solution as I'm not sure how else to get easily get a supply of fresh air.  Any idea how much heat will be lost through a top vent?

Offline pizzaneer

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Well, actually, the "fresh" air will come up from the bottom and in through the front opening.  

If you don't have an exhaust vent in the top of the box, the flame will die, because the hot, already-oxygen-depleted air will sit in the top of the enclosure.  You need to have a flow of air.  

This is what a top vent / chimney provides.  You can control the amount of airflow exiting out the vent with a damper.
I'd rather eat one good meal a day than 3 squares of garbage.

Offline jgame

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I would use a small adjustable vent on the backside, near the very top. That's what I have and no problems.
jgame

Offline Tampa

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Creation Ė got your PM.  A few quick comments.

I love your workmanship, the upper IR burner (esp. adjustable legs), the overall look and balance of the setup.  Really good stuff here.

Itís hard for me to visualize the heat flow.

Looking at the backside picture, Iím guessing the lower, stainless-colored vents, are the air intake for the lower burner(s) and the upper, black-colored vents, are the hot air exhaust.  Right? Did the original hood for this grill have an air vent in the upper area above the burners?  It must have had an upper heat vent (like mine) in the rear of the hood.  Otherwise the heat from the lower burners would only exit the back of grill never going above the grates when the lid was closed Ė I donít think they are designed like that.

In your modification, assuming the top hood just fits over the grill, it makes sense that some of the heat from the lower burners are blocked by a square pizza stone (? -  I donít see any evidence of a rotisserie or round stone) and exit the black area in the back.  The rest of the lower heat flows up the sides and into the hood building up until it exits the forward cutout slot.  Given the likelihood of hot air buildup in the upper hood, that top surface must be ďbugger hotĒ unless the stainless is double walled and/or insulated.  (Correct me if this is not true b/c it means I donít understand the hot air flow in this system.)

That said, what youíve created is beautiful, but it doesnít work right.  IMO, take off the hood and prototype something else with a roll of aluminum flashing from Home Depot and rivets.  Iíd want to understand and control that underside hot air flow.  Iíd block the side grates, maybe a little blocking in the front, so everything is forced out the back in the black-painted vents.  In my case I forced everything to the back of the grill then added a diverter to channel the hot air flow over the pizza and out the front slot.  (A lot depends on the stone Ė square or round Ė as to how you want to do this.)

Now that Iíve got the lower heat flow controlled, Iíd think hard about letting the IR burner do what it does best: radiate.  For this to work, I think you have to use a rotisserie, otherwise youíll get a rectangular char on the round pizza mirroring the shape of the IR burner.  I think you understand what Iím saying even though the char wonít really be exactly a mirror imageÖ

You might look at pictures of salamander broilers and/or cheesemelters.  They have gas versions that use the upper IR element and therefore manage the air intake and exhaust.  The general rule for grills and broilers is take the cool air in from the front and exit the back.  Only by hacking together prototypes will you get a sense of what works.

Regarding the vent/chimney idea, I think it has potential.  A flue doesnít do much IMO.  All you need is the vent, but angled away from the chef.  Again, Iíd prototype first.  Iíd try the vent at the back of the IR burner.  Assuming you donít have a lot of heat flow from the bottom, venting behind the IR burner should draw fresh air from the front slot.  But if you prototype it right, maybe you can switch the vent from front to back, or even to one side or the other of the top surface of the hood.

Iím out of time right now.  Iíll keep thinking about it.  Answering some of my above questions would help.  BTW, where are you located?


Offline creaton

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I would use a small adjustable vent on the backside, near the very top. That's what I have and no problems.
jgame

Jgame - Can you post of pix of your vent?

Offline creaton

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Tampa -  All very good questions and insights - Thanks.  Here are some answers on my end.

My lower burners are not having any problems running with the top on.  I've run it a few times with all three lower burners on and it gets to 750 in about 15 minutes easy.  I'm not exactly sure how the airflow works for my lower burners, but I didn't make any modifications here, so probably is operating very similar to its grill design other than the closed top that I've added in place of the original grill top.  My guess it that the fresh air is coming mostly through the black-colored vents, and the hot air is going out my pizza slot in the top.  With the original grill top on, I believe the hot air was escaping out the top-back like most gas grill designs.

In terms of the pizza stone/rotisserie design, here are some pix of how that works.  It is very similar to your design with a vertical rotating rotisserie and round 16" pizza stone sitting on top.   I guess you may be correct here that the heat is probably going up to the pizza slot level and existing.

My new oven top is double-walled SS and insulated with ceramic insulation.  It does still get hot, but not as much as it would without the insulation.

I like your idea of prototyping some top design with cheap aluminum flashing to see what works with blocking and vents.  Definetly much easier than destroying my double walled SS top. Then once I have a working prototype I can modify my SS top.

Hoping that my answers can help generate some more ideas!


Offline Tscarborough

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You could probably have built a brick oven for what you have invested in that.

Offline creaton

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You could probably have built a brick oven for what you have invested in that.

Very possible, Tscarborough!  The most expensive part was the grill itself, but I was able to get a steal on it during a Sears super sale in the spring + floor model discount. The top I was able to build for the cost of the SS sheet stock with the help of a friend. Other parts I've been able to find as scrap from friends that do work with SS.

Hoping it will be worth it in the end!

Offline Tscarborough

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What is the particular advantage of something like this over a regular old brick oven?

Offline creaton

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For me it is the mobility/portability of these units since I'm not particularly settled in any one geographic region and can just load this thing into a u-haul and roll; the small size as I don't have much space, and the fast heat up time (shooting for around 15 mins to hit 750-800)

Offline Tscarborough

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Fair enough, but the same principles apply:

A discrete thermal mass isolated and insulated, and in your case, adequately fired so as to be efficient.

Offline Jet_deck

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I will type again that IR burners are very rarely placed in a pointing down situation.  They tend to melt themselves. 

Just my .02 and and extra .01 for the propane.
Her mind is Tiffany-twisted, she got the Mercedes bends

Offline Tampa

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Jet - thanks for the comment.  But isn't it true that gas-fired salamander broilers and cheesemelters are common in this "pointing down" arrangement?  I have not fiddled with those devices, but I have fiddled with my grill IR and believe they use the same porus ceramic "sponge" as a burner - which should be OK in extreme heat.

Tscarborough - your comments are appreciated as well.  In my own grill experiments, I could have built a WFO from scratch and gotten fat(er) eating pizza by the time I finally had the bugs worked out on my rotisserie pizza grill.  Now however, I am quite happy with it - 20 minutes from ignition to yum.  By comparison, the overhead of a WFO (wood, warm up time, cleanup, space, etc.) isn't worth the incremental improvement for one lone Fatso and his skinny wife.  Maybe we need to host more events.

In full disclosure, I'm looking at a WFO this afternoon with my neighbor Bobino.  He's rich and is nuts about pizza.  I've always wanted to have a good friend with a WFO close by.

Creation - I'm still thinking about your situation.  It seems to me the problem has to be hot air buildup in the upper hood (w/o O2).  I think you need a topside vent.  Maybe even a large vent, if you are running 3 underside burners.  That heat rising past the black vents at grate level should draw in enough air to oxygenate the IR burner.  If the vent location is right and right-sized, you might be drawing cool air in from the forward slot.

Looking forward, since IR is cooking the top of the pie, you may need to either slant the IR burner (higher at the center, lower on the side) either that or diffuse the heat somehow in the center of the pie.  If you think about the radiant heat, perhaps you'll anticipate what I do - the center of the pie is always exposed to the IR burner but the rim is only partly exposed.  (I'm a good anticipator, but history shows that I'm often wrong in unique setups like yours.)  Prototype it first.

Dave

Offline shuboyje

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My home oven has an ir broiler looking down.  It hasn't melted yet
-Jeff