Petite Godin Custom Mod (for More BTU)

 
ringer19547
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Post by ringer19547 » Sat. Oct. 29, 2011 10:47 pm

Firstly, I've enjoyed lurking on this site over the years. Thanks to all the contributors.

I was burning in a Crane Coal Cooker (very respectable stove), after burning coal in a Triburner Stoker for several years, when I happened upon a Petite Godin. I was sure my wife would like the appearance and decided to give it a whirl. Well, she wasn't all that excited but I'm glad I tried it. It's a great little stove; easy to start and easy to burn. It will burn like a torch if you open it up. Having melted the paint on the ash door (as a novice), I can say that. The 5 inch stove pipe for the Godin is not commonplace so I used stainless steel truck exhaust pipe from the local scrap yard. Nothing rinky dink about that pipe. It came in 3 foot sections, is about 1/16 inch thick and could easily have a warranty for my lifetime. With galvanized pipe outside for insulation the chimney could suck a golf ball through a garden hose. I have a manometer, barometer, damper, hygrometer (not pertinent), outdoor thermometer and stack thermometer all in line with what I like to think of as my coal operations center. The issues now are too much draft and all the heat goes up the stack i.e. the Godin has thermodynamic short comings. Which leads to the custom mod...

The Godin burns inefficiently. The cylindrical shape and the secondary burn port burn the coal well, but all the heat goes up the chimney. So, how to improve the heat output? In my shed I found a piece of copper flashing (2ft X 3ft) left over from an addition I put on my old stone house years ago and which is now worth a pretty penny. I bent the copper flashing into a parabola and slapped it up against the backside of the Godin. That's it! A Godin with heat fins. The flashing more than doubles the surface area of the stove and noticeably increases heat output and air convection. When you feel the additional warmth, it doesn't look all that bad either!

P.S. In other posts people claim to fill the Godin stove up with coal to bank it for the night. How can you do this? If there is the slightest excess draft the entire mass of coal starts to burn and paint will start to melt. If there is too little draft the fire will die down. I put a couple inches of coal on the bed and it will burn for 8 hours with a stack temperature around 225F. Any more coal than that and I can't control the burn. Any answers out there?


 
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KaptJaq
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Post by KaptJaq » Sun. Oct. 30, 2011 12:16 am

Sounds like you may have an air leak somewhere. I have used the Godin 3721 or 3731 for over 20 years and never had an over-fire situation. I start the stove with a few pounds of coal. Once that is hot I add as much as she can hold. Once I see the blue flame start to dance on the top of the coal I reduce the air supply. I have put 40 pounds of coal in the stove and adjusted the air control to have it burn at 15K btu/hour for more than 24 hours.

If you cannot fill the stove and control the burn you may have a major air leak. Your strong draft is pulling too much air through the coal bed. The air control should limit this. When my stove is in steady state the air control is only opened about half to three quarters of a turn. Any less and the fire dies, much more than a full turn and she gets a little too hot.

Just for reference I have about 10 feet of 5" SS pipe that goes into an 8x8 clay line internal masonry chimney about 22' high. This provides me with excellent draft. While I do not have one, you may want to consider adding a barometric damper to your stove pipe to help control the draft and over fire situations.

 
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SteveZee
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Post by SteveZee » Sun. Oct. 30, 2011 7:30 am

That's my suggestion too. A barometric damper will help if you've that high a draft pulling on it. Also you need to see if you have that air leak below the fire some where and seal it up so you have better control.

 
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Post by grizzly2 » Sun. Oct. 30, 2011 4:42 pm

I concur with the above two gents. If air was not getting into the stove it would not burn too hot. A baro damper will help even out the burn rate once you find the air leak or air intake control problem.

 
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Post by nortcan » Sun. Oct. 30, 2011 6:00 pm

Hi ringer, could you send some photos showing your stoves' installation?
Like Steve and other said did you checked the lower parts of the stove for air leaks, check with a light inside the stove (easier whith a cold stove LOL) to find some poor seals. Try the dollar bill test for the doors testing?

 
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Post by rberq » Sun. Oct. 30, 2011 6:08 pm

Yes, please, pictures of the heat fins (and everything else).

 
ringer19547
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Post by ringer19547 » Sun. Oct. 30, 2011 9:44 pm

Thanks for all the responses. My wife is in disbelief of the number of responses, but what does she know? Real men burn coal and don't use stokers! (If any women are reading this, I'm just talking the talk.) After reading the responses, I looked for (using the flame of a match) and found a major air leak at the shaker handle and minor leaks around the ash door and the molding around the ash door. If I block the leak at the handle the temperature will drop 250F, a regular burn is 1/2 a turn rather than 1/8 a turn of the air intake, the burn characteristics change dramatically for the better and I'm happier than a pig in sh*t. Is there a gasket or grommet I'm missing for the shaker handle?

Savant KaptJaq, you are hereby my idle. I hope this isn't too personal, but how often do you shake and load and what is your stack temperature for an idle burn? Also, do you get a cavity under the burn? Thanks in advance.


 
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KaptJaq
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Post by KaptJaq » Mon. Oct. 31, 2011 12:03 am

Hi ringer,

As far as I know there is no gasket around the shaker handle. Some air does get to the bottom of the coal bed but the holes through the door frame and shaker grate frame are small enough that this is minimal. If, due to wear, too much air is getting in this way you can wrap some gasket rope around the shaker handle and push it into the space between the door frame and cylinder skin.

The leaks around the door and door frame would concern me. They may appear minor but both those seams are long enough that a series of minor leaks can add up to a lot of air. Is the gasket in place between the door and frame? When you "melted the paint" on the ash door did you warp it?

As to your questions:

My current stove is the 3721, rated at 37K btu/h. I believe the 3270 you have is a smaller stove rated at 15K btu/h. The difference has to be factored into my answers.

When I burn coal I tend to the stove about every 12 hours.

Depending on the quality of the coal sometimes when I shake the grate I do get a cavity under a bridge of burning coal and ash. The better the coal (lower ash, less clinkers) the less frequently the bridge happens. I shake first then add coal. The weight of the new coal usually collapses the bridge.

I normally burn my stove at 15-20K btu/hour. At that burn rate the stack temp is around 500 degrees about a foot above the stove with a condor flue probe. As a note these flue probes are not know to be terribly accurate. I use mine more for relative temps to gauge how my burn is doing.

 
rberq
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Post by rberq » Mon. Oct. 31, 2011 3:08 pm

KaptJaq wrote:The leaks around the door and door frame would concern me. They may appear minor ...
It is surprising how much air can leak through small spaces. There were a couple holes below my grates, each one much too small to fit a pencil through, but until I plugged them the stove temperature would run away to 350 degrees with all other inlets closed.

 
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Post by ringer19547 » Tue. Nov. 01, 2011 8:23 pm

KaptJaq.

Many thanks for all your help and thanks to the other posters. Two of the three air leaks, I suspect the Godin factory is a bit too close to the vineyards, have been blocked and the burn has improved dramatically. Having a Godin 3721 and not a 3720 (it's a bit confusing the names and model numbers), I've been able to follow your suggestions with great success: much less futzing for the next 20 years, longer burn times and much more heat. I appreciate the Petit Godin design more than ever.

Just one more question: If your burning at one half capacity (18 btu/hr) and the stack is 500F, what would the stack temperature be at full capacity? Holy mackerel, I thought 500F was on the hot side!

Thanks again.

 
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Post by ringer19547 » Tue. Nov. 01, 2011 8:31 pm

Sorry, but I'm not really setup for photos. Perhaps if you visualize a Petit Godin with angelic wings which double as heat fins. The reality is much bleaker, just some sheet metal attached to the back of the stove.

 
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Post by rberq » Wed. Nov. 02, 2011 6:41 pm

ringer19547 wrote:Just one more question: If your burning at one half capacity (18 btu/hr) and the stack is 500F, what would the stack temperature be at full capacity? Holy mackerel, I thought 500F was on the hot side!
Yes, 500F does seem very hot. My stack temperature right at the stove collar does not get that hot even at a very high burn rate. So probably you are STILL putting a lot of heat up the chimney, even after the improvements you have made. You said you have a manometer -- what reading does it show when the stack temperature is at 500F?

As a couple people suggested you might need a barometric damper to regulate (reduce) the draft and leave a lot more heat in your living space. You would then have to dispose of old golf balls some other way than having them sucked up the chimney, but it would be well worth it with less coal consumption and more heat. Let us know what the manometer shows....

Edit: Oops. I see it was KaptJaq, not you ringer, that has a stack temp of 500F. So now I want to know HIS manometer readings as well as yours. 500F with a probe equates to maybe 300F surface temperature, which is not terrible but is still kind of high.

 
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Post by ringer19547 » Fri. Nov. 04, 2011 5:28 am

rberg, kaptjaq, et al.

In my quest for the ultimate combustion experience, I've installed a barometric damper and plugged the air leaks. Life is good. Reading about .04 inches of water, before the damper (because the stove pipe is cooler and my manometer connection is plastic), at a stack temperature of 500F. Getting 10+ hour burns at 400F rather than 8 hours at 200F (if I was lucky) and I'm only days into learning the ways of the beast! Question: what is the optimal stack temperature for burning coal?

KaptJaq and other Godin-ites: The shaker handle rod goes through the sheet metal of the stove to the grate. That's it. The hole in the sheet metal is rather large, you can stick your finger in it, and it gets larger with shaking because the rod rubs against the sheet metal. If you point a flash light into the hole you will see. Initially the reasoning behind the design completely eluded me, but upon further consideration perhaps the hole is intentional and allows air to circulate to the back of the stove. The air coming in the hole will create a vortex under the grate, that's ingenious. However, still pondering that one...

rberg: the surface temperature of a Godin may be only 20 degrees less than the stack temperature because of the Godin design. It's hot. P.S. Isn't Dickens great!

 
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Post by SteveZee » Fri. Nov. 04, 2011 1:58 pm

Ringer,

I think I would make some kind of bushing for that shaker handle hole, first so as not to make it larger, and to give your shaker handle a little more solid mounting. Washers would block off the leak some and could work for the bushing if you had a way to tack them to the sides. You really want to be able to control all the air that you possibly can. Regarding your stack temps 500 is way high unless it's wide open when initially starting a coal fire. Both of my stoves have stack temps under 180 degrees once the stoves have stabilized at a given setting. My stack temps are usually half or less than the surface temps the stoves are running at. So, say I'm cruising at 400 degrees on the barrel of the Herald, the stack temps would be 180 or so. I understand that the Goden is direct vent so they might run higher but 20 degrees difference doesn't seem right? Very inefficient.

 
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Post by franco b » Fri. Nov. 04, 2011 6:45 pm

All the Godins I have seen have the shaker ring going through the cast iron. The ring is threaded. Un-thread it and install a fender washer on the shaft to block the opening.

The ideal stack temperature is 250 degrees all the way to the top. Any less causes condensation of the flue gas and corrosion, especially in stainless chimneys. The ideal stack temperature for maximum efficiency of the stove is as low as it can be and still maintain draft.


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