Garn is surging

Dunno about Garn, but my EKO will do that if I have too much primary air combined with wood that's really dry or has a lot of surface area.

HW - yep, the GARN, Switzer, and just about any combustion appliance will do that. It happens especially with really dry fuel with lots of surface area and high primary air flow. The rate of combustion actually starts to exceed the (enormous) rate of air supply. It will briefly starve, burn rate drops, then when supply catches up, you get a brief flashover, causing the puff. It happens rapidly and cyclicly, as you found out.

When you got your GARN there should have been a loose refractory brick in the fire box. Per the instruction manual, you can use that brick to deflect the flow of the primary air coming out of the lower nozzle/outlet. stand the brick on its long edge about 6-8" from the lower outlet. That will defelct some of the air up, and slow the rate of primary burn. This does not always eliminate the puffing, but it does help. Experiment with the distance from the outlet, and I sometimes play with the angle it sits at too. Mine has actually cracked in two, which I like since I can stagger the pieces and adjust the air flow more easily.

Try reducing the amount of fuel, packing the fuel tighter (less air space between pieces), and even mixing in a little green/wet wood to reduce the burn rate. There is a learning curve with the fuel supply and type.

BTW - if you are getting sparks/ash pushing out while it is puffing, try tightening the door seal by spinning the inner door disk a half turn CCW.

I am contemplating a mod to my GARN air supply. Similar to but not as drastic as TCaldwell has done. I just want to add a deflector/damper before the air gets to the lower nozzle. That way I can adjust primary air flow externally if/when she starts to puff.

Jetstreams will do it too if you have too dry or too finely split wood. Solutions are listed above. Using bigger pieces is the easiest as it saves work spliting.

Also is worse with softwoods than with hardwoods.

hedgewood, the problem, too much primary air, and the manifestation of puffing can be reduced as described above, as suggested you can still have a full load just mix the moisture content , also try carefully pushing the wood towards the back of the firebox, away from the primary air outlet. Also make sure the combustion air inlet has no other piping attached to it that will impede flow, likewise on the exhaust, no spark cap or deflector. through trial and error you can greatly reduce this, ----, all [controlling] beyond this point has diminishing returns on the rate of investment. the design if the stock aircollar does not allow for seperate primary and secondary air control, the easiest way to read what i have found would be to scroll down the boiler room threads to 02 control for the garn,

short answer: You have more fuel than air available to burn it. I would hazard a guess that your wood is fairly dry and burns readily and quickly. Try mixing some "greener" fuel in with your loads and see what happens.

One of my customers with a new 1500 (he has 2 other Garns besides) was consistently running into that phenomena this season due to the fuel being very dry (<18% MC) red and white oak. Experimenting with it led to the realization that less than half a normal load would still make it chug. He is now using about 1/3 "green" and 2/3 of the very dry stuff. The green stuff he has was cut in 8' sticks last winter and only recently buzzed into usable length. The dry stuff has been cut, split and stacked under cover for 3 years. Larger pieces of unsplit wood will help also.

hedgewood, instead of a brick, try a short piece of 2x4, it will deflect the primary air initally, when needed and be burnt when you want to burn coals.

TCaldwell said:

hedgewood, instead of a brick, try a short piece of 2x4, it will deflect the primary air initally, when needed and be burnt when you want to burn coals.

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And the above is why I check the Boiler Room every day. Tom, that is a brilliant idea. My brick has broken into two smaller bricks, and I have often tried to prop it against some wood in a manner that would make it fall over as the wood burned. This is better/smarter.

actually that trick was passed on to me by a garn distributor, thanks anyway

slowzuki said:

Jetstream will do

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You are the only Jetstream owner that I have found on this site! In this area ours is the only one of three are still in operation, not including our spare! Of the 900 or so made, it would be interesting to know how many are still in operation. Have you any idea how many may still be going in your area? :exclaim:

I had that with the Atmos when I had kiln dried(pallet) wood in it. I am now using 4 to 6" splits & rounds for the early burns as Atmos says & real large rounds later. There is no more puffing & surging, Randy

Dosn't have to be a 2x4 either. You know those little quarter "cookies" you get from a short log? They work great for exactly this purpose. Especially when the ashes have been recently removed from the Garn, I find I need to place something in front of the nozzle to mix the air...else I may get a bit of smoke...not enough secondary air for the burn. So I use a short piece of wood, a little piece of a "short log", etc. just to deflect the bottom air feed away from going straight into the fire. Works like a charm. This tip came from heaterman last year.

In fact, I find myself looking for these little pieces...I might actually start cutting some on purpose and stacking separately. I've never had any remnants of this little piece either...it's always fully consumed.