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Rocket stove help!

 
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Hi all, I'm new to the forum and like all the info I find here, but I need a bit of expertise to help me with my rocket stove project. I've been building and tweaking this rocket stove over the summer and I'm really satisfied with the way it performs. I designed it to run on pellets which it does very well. There's a gate that controls pellet flow, as well as a damper and ash tray on the intake side. Running the stove wide-open, I hit 670 °F with a 4 foot section of stainless 6 inch pipe.

I was excited to get it installed in my RV for winter camping trips, but I've hit a huge snag. It fires up and drafts alright, but it gets nowhere near as hot as before. I could hear the stove roar before, but now its almost a sputtering sound. The stove and fuel are the same, but I've added two elbows for an offset, as well as a 2 foot length of B vent and a rain cap. Is the offset or chimney length causing the issues? I'm pretty bummed out at the performance drop and any help would be appreciated. This is my first large rocket stove build and I'd like to see it run right, it's getting chilly out there!
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Location: Pee Gee, Bee Cee, Cee Aye En Aye Dee Aye
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I'd suspect the clearance in the rain cap first, if removing it for a test doesn't make enough of a difference, I'd try extending the chimney.
 
pollinator
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Location: Penticton, Canada
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building woodworking rocket stoves
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Hi Brian,  What Alley suggested is a good idea. What also comes to mind is the inside air pressure causing it to slow down draft. Have you opened a window to see if that helps?  BTW, cool stove!
 
Brian Legend
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I tinkered with the stove again yesterday, removing the cap made no difference. I even put a small fan in front of the intake, and not much difference. I opened a window and got slightly better draft. What I noticed is when the pellet hopper is nearing empty, the burn gets considerably hotter, like the stove is getting more air. I held a piece of paper in front of the hopper and the draft held it on! I heard the familiar roar of the rocket again. The inlet on the stove is 4.5 x 5.5 inches, and my chimney is 6 inches. Maybe too large an exhaust pipe, or too small an air intake?

I'm beginning to think I was fooled a bit when I was running the rocket outdoors as it was getting lots of air. I don't know if I should get a reducer and run 4 inch stove pipe which is getting harder to find, or modify the stove to get more air. Kinda scratching my head with this one.
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gardener
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Where does combustion air enter, just through the pellet hopper, or the ash door too? I see a wooden handle; what does that control and how?

If your draft is too slow, reducing anything will not help. The longer chimney than your outside trials might restrict draft, or if hot might increase it. Testing outdoors with an identical chimney might be instructive.
 
Brian Legend
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Glenn Herbert wrote:Where does combustion air enter, just through the pellet hopper, or the ash door too? I see a wooden handle; what does that control and how?



The air enters through the bottom through the ash door, a bit of air also enters the hopper when the pelletts get low. The effect seems more pronounced when I run the stove inside. I was going to make a cap for the hopper but read that wood gas might fill up the hopper.

The wooden handle controls the amount of pellets coming in to the burn chamber. So, pulling the handle down will raise the gate in the hopper allowing more fuel in. The lower yellow handle controls how much air comes in. I usually run the intake full open, unless the fire burns too hot.

The only idea I had was inserting a metal sleeve in the hopper to get more air into the burn chamber. When I had the paper covering the hopper, I moved it so there was a half inch gap and the stove roared back to life. The other idea was to cut the bottom of the stove off and add another inch of metal. I don't want to go through all that chopping and welding if it won't work though.
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Brian Legend
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I think I had a eureka momment. I made a small sleeve out of some scrap and put it in the hopper to get more flow into the burn chamber. I lit the stove and it's burning way better. Would I be able to cut holes on the sides of the hopper near the burn chamber and tack on some metal screens or is there going to be a problem of getting monoxide geeting out?
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Location: Wellington, New Zealand
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Carbon monoxide is formed at the point of incomplete combustion and the draft will carry it out the chimney.  If it smokes back you'll get CO coming back.
But you'll need a CO detector near by with any appliance that burns inside.
 
Brian Legend
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Graham Chiu wrote:Carbon monoxide is formed at the point of incomplete combustion and the draft will carry it out the chimney.  If it smokes back you'll get CO coming back.
But you'll need a CO detector near by with any appliance that burns inside.



Thanks for the tip, I haven't seen the stove backdraft yet. Most appliances in the RV are propane and work well and up to snuff. I'm going to invest in a dual smoke/O2 detector because of the stove.

A trick I learned from my dad was to hold a lit cigarette in front of an appliance that has a cumbustion air intake, and if it draws the smoke in, you're likely ok.
 
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