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dont let your stored thermal mass escape through the chimney

Posts: 15
Location: durham nc
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for those without batch burners or doors on the feed tube

so i noticed between burns in the moderately cozy temp in my house that i have set up the perfect escape rout of my stored heat the chimney

easy fix plug hole when fire is out

noticed a massive draft after fire was long gone you couldnt light a lighter in front of the chimney so much air was rushing out 12 hours after a burn

i have 30'+ flu through 350 gal of water 3yd of sand rock and cobb on a slab to store heat in so i can get a nice draft movin through the drafty house when their is a substancial temp differntial inside to out

energy doesnt like to loiter make it work to escape the home
keep the heat whatever that means
Posts: 3733
Location: latitude 47 N.W. montana zone 6A
cat pig rocket stoves
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I noticed the same thing in our greenhouse... BIG draft at the feed tube. Standard practice is cover it up every night ! There is so much draft in the morning that I use 2 larger pieces of wood to block 90% of the burn tunnel and then I add paper & kindling and other than still blowing out the lighter , it takes rite off.
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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A late welcome to Permies.com, our sister site, Richsoil.com, and the Rocket, Wood stove, and Cob Forum Threads, With 29,000 Fellow Members
Worldwide, you can come here 24/7 and find someone who wants to talk about what you want to talk about !

I noticed in your Dec 23rd 2014 Thread that you have a horizontally fed or L-shaped RMH System, without doors or a way to block off the thermo syphoning
of warm air through your system, you will have a continuous heat loss from your system !

The Vertically fed J-Bend style RMH has a couple of advantages over the L system, very soon after your fire is out The J-bend style will act like the water trap
under your kitchen or lavatory sink preventing this Thermo syphoning, It is also an easier system to manually cap off After the Fire is out ! and burns a
little hotter and cleaner soon, and needs no periodic shoving of Your Wood Fuel forward to reach tits sweet spot where it burns best- Also this reduces the likely-
hold of shoving live coals and charcoal ahead of the fuel reducing the affective size of the Burn tunnel and potentially causing smoke back

While rare with the Vertically fed J-Bend accidentally shoving coals and ash and charcoal a head and reducing chamber size Can happen with the Vertical Feed

For the Good of the Craft ! Big AL !
Posts: 219
Location: S.W. Missouri, Zone 6B
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I just put fire brick over the feed tube opening, although that is not a perfect seal, so after a couple hours I will then remove them, lay a piece of aluminum foil over the opening, a couple spare pieces of tile I have that are larger than the opening, and then put the fire brick on top of that. Kinda ratty looking, but right now the whole thing is in build-modify mode anyway, so that's not important right now.

For a nicer finish, I think something else would be better. Perhaps pouring a plug to drop in (basically like casting a core, or more specifically, like making a capping plate as used in masonry heaters). But these are basically the same techniques one uses to seal the clean out doors. So whatever works there could be implemented at the feed tube with some forethought. That said, I think the easiest thing to try is finishing the facing material around the feed tube with a smooth tile-like finish, and then getting a capping plate that has some kind of an air gap seal under it to fit just around the feed tube opening. Just like you do on doors and windows.

I'm kinda thinking some granite tie might look nice in this application. Hard stuff, so it would certainly take the accidental knocking of wood going into the feed tube. And as tile it can be found very smooth, which will make brushing any ash and debris into the feed tube simple, and then just set the cap over the feed tube opening, made an inch or so larger on all sides than is the fire brick lining, so that the edges of the cap is pressing down against the granite, and where the cap and granite touch, that's where you put the seal. It could be as simple as foam or rubber that is used as threshold sealing for doors. The only added caution is to remember to only put this on after the surface is cool enough, so as to not damage the seal / gasket material.

For your L-type rocket, I think I'd just cast a door/plug and after I know the fire has been out long enough for the draft to take away toxic fumes, I'd just plug the opening. Again, some foam or rubber gasket material might help.

Or rope, like is used on wood stove doors. That may be a better idea anyway, as that is designed as this kind of seal/gasket heheh

Just thinking out loud here. I'm not yet worried about this point, in terms of making it pretty to look at. My "gasket" material is the sheet of heavy aluminum foil, and I get an even pressure by setting the larger tile over the entire opening, and then add weight by adding the fire bricks I used to control the air gap whilst burning. But that is an ugly solution (although it does seem to have been effective so far).

Edit: Or use rock wool as the seal/gasket material. That should work well and be able to take high temperatures.
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Erik Weaver wrote:I just put fire brick over the feed tube opening, although that is not a perfect seal

I found out by accident that a square paving stone fits a 5.5 x 5.5 inch opening ( a 6 inch system) just nicely . . . has about 1/8 of an inch spacing here and there, but I figure it gives all those hot embers air too burn up . . . really cuts down on the draft thru the stove . .
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