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rocket mass heaters

HELP!! Getting blowback

Posts: 55

Location: Shenandoah Valley

posted 8 years ago

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Hello All,

HELP! I had a traditional J-shaped rocket mass heater with a 55 gallon steel drum for a bell.

I rebuilt my traditional stove, and put the improvements Dr. van den Berg suggested into the burn chamber (the arrow, and the curve at the back.

Since rebuilding, the J-tube, I have some kind of issue. Basically, the stove works moderately well for about 5-10 minutes, and then my house fills up with smoke, and won't draw any more.

I checked that all of the exhaust lines are clear, as well as the chimney. The riser is 2" thick firebrick, with a 2" layer of rock wool insulation around the riser.

One other improvement I did between last year and this year was to add a chimney shelter.

Any thoughts appreciated.

"Let him who possesses a field, so partake of its yearly fruits, that he may not suffer the ground to be injured by his negligence; but let him endeavor to hand it down to posterity as he received it, or even better cultivated. Let him so feed on its fruits that he neither dissipates it by luxury, nor permits to be marred or ruined by neglect."

John Calvin

Glenn Herbert

Rocket Scientist

Posts: 4526

Location: Upstate NY, zone 5

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posted 8 years ago

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If the core is the same as before except for the addition of the tripwire and backsweep, something else must have changed for its behavior to have changed drastically. Tell us more about the chimney shelter. Also, more details about the overall system, its setting, your climate, and how it performed last year would be helpful in diagnosis.

Adam Jonathan

Posts: 55

Location: Shenandoah Valley

posted 8 years ago

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Glenn Herbert wrote:If the core is the same as before except for the addition of the tripwire and backsweep, something else must have changed for its behavior to have changed drastically. Tell us more about the chimney shelter. Also, more details about the overall system, its setting, your climate, and how it performed last year would be helpful in diagnosis.

Hi Glenn,

the chimney shelter is made for a variety of sizes (it's adjustable), and looks almost exactly like this:

https://jet.com/product/detail/acca05b578a046818db4ae30924a6bb1?jcmp=pla:ggl:a_nj_dur_gen_hardware_a2_b2:heating_ventilation_air_conditioning_a2_other:na:PLA_649032425_30291306262_pla-161719582140:na:na:na:2&code=PLA15&gclid=CMDz7bDGmdACFYb1MgodK1sLSA&gclsrc=ds

Last year, the only problem I had was a birds' nest in the flue, which is why I put in the chimney shelter

Otherwise, last year was a great year. Part of my barrel was clogged with ash, so I took the whole thing apart, and tried to do the van den Berg improvements. One improvement he suggests is a cured piece at the end of the burn tunnel, just under the heat riser. That sticks out about 2" plus, so maybe that's my problem???

Glenn Herbert

Rocket Scientist

Posts: 4526

Location: Upstate NY, zone 5

574

posted 8 years ago

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Ah, okay, a cap for the top of the chimney. It doesn't seem like that should make much difference in draft.

What is your system size? 6", 8", ? Can you post a sketch of exactly how you made the backsweep? That should not narrow the channel significantly, basically filling in the dead back bottom corner to make smooth flow along the outside of the curve.

Byron Campbell

pollinator

Posts: 293

Location: US, East Tennessee

posted 8 years ago

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This does sounds like a restriction problem. Was the barrel removed for the core mods? What is the top of the heat riser to barrel gap? If it's really tight, less than 2 inches or so, then the barrel top could be sagging / dimpling in with heating and further restricting flow out of the riser as the stove comes up to temperature.

The rocket burner's back sweep "kick tail" addition, if it is restricting CSA at the transition into the base of the heat riser, could also present a problem.

Last but not least, was any work done to the manifold area that could restrict gas flow from the barrel into the horizontal ducting?

Just a few ideas. Hope you get it figured out, cold weather is fast approaching.

best regards, Byron

John McDoodle

Posts: 617

Location: ontario, canada

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posted 8 years ago

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Must be one of your "improvements" if last year was great.

A quick way to eliminate guesswork would be remove the chimney cap. If that works, great, but I have a feeling it's not the cap.

I'm curious: What is this tripwire kick-tail and why have I never heard of this? Also, Was your riser wrapped in wool last year also?

positively optimistic 🙂 https://www.youtube.com/@613Builds

Glenn Herbert

Rocket Scientist

Posts: 4526

Location: Upstate NY, zone 5

574

posted 8 years ago

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The tripwire and backsweep with kicktail are part of the refinements made by Peter van den Berg to the standard J-tube before he started developing the batch box design. The tripwire works with the p-channel which is a secondary air injection port to create beneficial turbulence with the injected fresh air in the heart of the burn tunnel.

7" Core with TripWire/P-Channel/KickTail - Design

If you look at Dragon Heaters' designs, they are licensed directly from PvdB for US distribution. How Rocket Heaters Work

I agree. Here's the link: https://woodheat.net