DIY secondary burn

[DaveNY49]

I’m seeing many people who have successfully made a secondary burn set up for their stoves. I just bought an old used Bullard stove. It has a thick (2 inches) hollow baffle. And comes with a blower on the back. If what I’m seeing in a secondary burn system is correct,…it’s basically air coming into the top of the firebox pushing down on the fire and burning the smoke and gases? I’m wondering if I could drill a series of holes in the hollow baffle creating secondary burn effect? And leaving the blower off would leave an opening for draft to he holes. Am I off on my theory?

Thanks

 

[stoveliker]

In principle yes.
The relevance of the blower depends on the path of the blown air. Are you saying it blows air into the baffle and then out I to the room?

If the blower does have to be off for.your secondary combustion to work, I suspect you may get less heat from the stove with secondaries but without blower. It may be cleaner burning but might not result in more heat in the room?

 

[begreen]

As noted in the other thread, the baffle may not be stock. At least it doesn't show in the manual. An air supply pressurized by a blower sounds like a way to turn it into a forge. It's a tough old stove, but that would overfire it quickly.

 

[DaveNY49]

In principle yes.
The relevance of the blower depends on the path of the blown air. Are you saying it blows air into the baffle and then out I to the room?

If the blower does have to be off for.your secondary combustion to work, I suspect you may get less heat from the stove with secondaries but without blower. It may be cleaner burning but might not result in more heat in the room?

So I’ve been researching secondary burning stoves today and it seems that a secondary air intake gets its air from outside of the stove at room temp. So my plan was to remove the blower from the stove. Which would leave an opening on the back of the stove. An opening that leads to the hollow baffle.

The original design is that the blower blows forced air into the back of the stove up a chamber into the hollow baffle which exits out either side of the stove through a small vent. Since the baffle is hollow I was thinking of making use of it and utilizing it as secondary air tubes. The air woukd follow the draft up through the back of the stove (if there is any draft there at all) , into the hollow baffle , and out the holes of the bottom of the baffle that I’d drill.

I’m just not sure how many holes, how far apart, and what size I should drill. And if there would be enough draft. There wouldn’t be a cut off valve for this make shift secondary air either. It would always be there.

 

[stoveliker]

Yes, that was.my understanding.

I don't know the size or spacing of the holes that you need
As it wasn't engineered, it'll be trial and error.
I'd Start with 2 rows,.one at the front, and one in the middle of the baffle, with 1/8" holes that are 1" apart. But I have no experience.,.

 

[begreen]

There must be no connection between the convection cavity and the firebox cavity. Otherwise there's a chance for smoke or CO to enter the room, especially at the late stage of the burn.

 

[stoveliker]

That's a good remark.

But isn't secondary air coming from the room (as always) not the same risk?
Or are you saying any natural convection in a (otherwise fan forced) hollow part might suck out gases more than the natural convection around the stove?

 

[begreen]

It's an unknown, but a possibility of greater risk due to the input and output openings for this convection baffle being large. It's hard to say how convection will change during various stages of the burn. I'd be more comfortable seeing a secondary rack put in right below the convection baffle. This could be done with plumbing pipe.

This is all without actually seeing the setup.

 

[gruesome]

This is also all assuming that the firebox is sealed well enough so it will pull in air from the holes drilled into that baffle. I'd check the door gasket tightness, and how low you can turn down the primary air.
There is also no reason to leave the blower opening open; as you said, there are openings for the blower air to escape from the baffle, and those will be enough to draw air in.