Secondary burners added - One question about insulator over baffle.

[Dra2650]

A little history. My brother-in-law & I built my stove some 28 years ago. Modeled after his Fisher, so essentially an airtight box. The only differences are my primary air enters from the rear, the door is a hinge down, and mine is 3/16" plate (instead of 1/4", I think). It is still in really good shape. It was our only source of heat for the 1st 4 years. Since, it has been a used with our heat pump. Days below 50 and nights below 35 is my standard for when I burn a fire. I can get the stove hot, pack it full at bedtime, dial the air back, and still have large hot coals and heat radiating 8 hrs later.

Adding secondary burners caught my eye this winter (brand new to me). I watched a lot of Youtube videos, read many very long threads her and other sites, and even "white papers" from manufacturers. I have attached a drawing of my heater (black is the original stove layout) (blue is the added burners and baffles) (the fire brick is in brown just to make it easier to visualize and has always been there). The plumbing routing is not shown... just the secondary intake and outlet positions.

Finally, my question. Do I need an insulator on top of the SS baffle above the burn tubes? What is it's purpose? I have seen comment here and elsewhere, that it is to protect the stove top from direct heat. I have also seen that it is to absorb heat to keep the SS baffle hot as the "cooler" air hits it. Which is it? Maybe it is both.
The air gap above the baffle is in the 3/4 - 1" range. To me that seems sufficient for the protection argument. Am I correct?
If the reason is to properly maintain the temp of the baffle, my plan it to use cement hardibacker board. Someone posted that they had success using it. A ton cheaper than ceramic blankets. I would like to not need it just for the added weight on the tubes.

So, for my stove, is an insulator beneficial, needed, required, etc... and why?

Thanks in advance.

 

[Del_]

The baffle is about keeping the area of the secondary air tubes as high as possible. Then when the fresh hopefully pre heated secondary air enters the firebox in this hot area secondary combustion takes place. I believe around 1,200°F is the target temp. Once secondary burn starts the area gets hotter. My Jotul F600CB has a very convoluted secondary air path for preheating and 7/16" cast iron panels for the baffle. About a 1" sheet of some type of insulation is on top of the baffles. The glass doors are an important part of monitoring the secondary combustion system. Once it 'lights off' the main input air can be reduced to a lower lever but if air is reduced to soon then low efficiency burning and high smoke output take place. I've been watching and running this Jotul for 15 years now. I experimented for several years about 5 years ago making the secondary air adjustable because once all of the pyrolytic gasses are burn off and all that is left is a bed of coals efficiency can be increased by cutting off all secondary air. It wasn't worth the monitoring time but some type of automatic system would be neat.

 

[brenndatomu]

A little history. My brother-in-law & I built my stove some 28 years ago. Modeled after his Fisher, so essentially an airtight box. The only differences are my primary air enters from the rear, the door is a hinge down, and mine is 3/16" plate (instead of 1/4", I think). It is still in really good shape. It was our only source of heat for the 1st 4 years. Since, it has been a used with our heat pump. Days below 50 and nights below 35 is my standard for when I burn a fire. I can get the stove hot, pack it full at bedtime, dial the air back, and still have large hot coals and heat radiating 8 hrs later.

Adding secondary burners caught my eye this winter (brand new to me). I watched a lot of Youtube videos, read many very long threads her and other sites, and even "white papers" from manufacturers. I have attached a drawing of my heater (black is the original stove layout) (blue is the added burners and baffles) (the fire brick is in brown just to make it easier to visualize and has always been there). The plumbing routing is not shown... just the secondary intake and outlet positions.

Finally, my question. Do I need an insulator on top of the SS baffle above the burn tubes? What is it's purpose? I have seen comment here and elsewhere, that it is to protect the stove top from direct heat. I have also seen that it is to absorb heat to keep the SS baffle hot as the "cooler" air hits it. Which is it? Maybe it is both.
The air gap above the baffle is in the 3/4 - 1" range. To me that seems sufficient for the protection argument. Am I correct?
If the reason is to properly maintain the temp of the baffle, my plan it to use cement hardibacker board. Someone posted that they had success using it. A ton cheaper than ceramic blankets. I would like to not need it just for the added weight on the tubes.

So, for my stove, is an insulator beneficial, needed, required, etc... and why?

Thanks in advance.

View attachment 802111 View attachment 802111

In your case, its possible that having a baffle there is going to hurt you...it is severely reducing the exterior stove surface exposed to the fire/hot gasses. But, without the baffle there, your stovetop is being exposed to some intense heat too...so that could be an issue? As Del said...you can be talking about 1200*F, and higher there.
With the baffle to the rear, like in most designs, the baffle keeps the smoke/wood gas right at the hottest part of the whole firebox (at the early stages of the fire, where secondary burn does the most good) and right where the preheated secondary air is applied. The baffle then also elongates the path to the stovepipe connector...which gives residence time and maximizes the amount of stove surface area that the exhaust has to pass by...but the stovetop would not be directly exposed to the intense heat of the secondary burn, like your design would with no baffle in place.
To answer your question though, I think the baffle is often made of an insulative type material (or has some added) to keep that area as hot as possible

 

[Del_]

 

[Del_]

Del first draft

 

[babybart]

I would think the fibers in Hardiboard would break down to fast. You can get ceramic board online that is better suited to this application.

 

[Dra2650]

Thanks all.

Let do some thinking.

 

[tla100]

Mine is like Dels pic. Secondary burners go all the way to back. 6" exposed in front. There are ceramic type tiles above tubes and also a ceramic blanket on top of tiles. 3" between top of stove and top of blanket. 6" opening in front to the door.

 

[tla100]

Not sure how the reburn works on mine. It will roll pretty good and down the front of the glass and also flames shooting out of tubes.

 

[tla100]

This from my user manual.
1st a side view. 2nd a blown up diagram