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[vpd66]

Ok, I've been planning to build a Garn style wood boilder for quite a while. I have the shop, I'm a welder by trade, I've researched how it works and have worked out the dimensions. I've seen Petemoss and Canuck's builds and I've been just waiting for the right sized tank to come along to use. I've found some used tanks, but there either too long or too small of diameter. Anyway, my question is how does this design achieve secondary burn? I understand that it has a refactory insulated secondary chamber, but doesn't it need to have air injected into the secondary burn chamber? All I see is where air enters the firebox around the collar of the door. Shouldn't some additional air be piped to the secondary burn chamber? Maybe I'm missing something.

[Canuck87]

In a Garn there is an air inlet at the top of the firebox and one at the bottom as you probably already know. The air from the bottom inlet flows through the wood load and fans the fire. Air from the upper inlet flows mostly across the top of the firebox away from the flames and then drops down to be sucked through the secondary where it mixes with any unburnt fuel and burns. Any smoke that comes from the burning woodload is extremely hot and just needs the added bit of oxygen to burn. I ran air tubing back to the secondary but the Garn design works great on its own so I don't think it is really helping me any. Having the secondary air flow through the hot upper part of the burn chamber might be an advantage.
One thing I noticed on a Garn design is that the secondary is almost at the bottom of the firebox. I don't know why it is but I assume there is a reason.

Good luck with your build, I'm excited to see how it comes together.

[vpd66]

In a Garn there is an air inlet at the top of the firebox and one at the bottom as you probably already know. The air from the bottom inlet flows through the wood load and fans the fire. Air from the upper inlet flows mostly across the top of the firebox away from the flames and then drops down to be sucked through the secondary where it mixes with any unburnt fuel and burns. Any smoke that comes from the burning woodload is extremely hot and just needs the added bit of oxygen to burn. I ran air tubing back to the secondary but the Garn design works great on its own so I don't think it is really helping me any. Having the secondary air flow through the hot upper part of the burn chamber might be an advantage.
One thing I noticed on a Garn design is that the secondary is almost at the bottom of the firebox. I don't know why it is but I assume there is a reason.

Good luck with your build, I'm excited to see how it comes together.

Thats kind of how I thought it worked. Seems too simple when you compare it to a down draft gasifier. I'm still in the planning stages and searching for a tank around 6ft diameter and 8ft long.