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#292347 - 09/10/16 01:46 AM Re: Count Rumford [Re: pondering_it_all]
logtroll Offline
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Registered: 04/26/10
Posts: 8647
Loc: New Mexico (not old Mexico)
The ash dump door came today and I got some more of the herringbone firebox laid up. It's a little rough because I'm cutting the 2"x2.5" out of the original firebricks salvaged from the demolition. The voids behind the firebox I'm filling with demolition rubble and a mortar made using mortar mix, vermiculite, and concrete foamer.

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#292350 - 09/10/16 02:12 AM Re: Count Rumford [Re: logtroll]
Spag-hetti Offline
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Registered: 09/10/08
Posts: 1593
Loc: Middle, USA
Wow. Looking good. Where does the ash dump go? Some place fire proof, I hope.
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#292351 - 09/10/16 02:13 AM Re: Count Rumford [Re: Spag-hetti]
logtroll Offline
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Registered: 04/26/10
Posts: 8647
Loc: New Mexico (not old Mexico)
It goes to the ash hole, what'd ya think?
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#292352 - 09/10/16 02:20 AM Re: Count Rumford [Re: logtroll]
Spag-hetti Offline
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Registered: 09/10/08
Posts: 1593
Loc: Middle, USA
Ow. And I did it to myself. Thanks for being so you. Do you burn in your fireplaces or just erectum?
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#292353 - 09/10/16 02:34 AM Re: Count Rumford [Re: Spag-hetti]
logtroll Offline
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Registered: 04/26/10
Posts: 8647
Loc: New Mexico (not old Mexico)
Since you asked, one does have to wait for things to stiffen up before lighting the fire.
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#292355 - 09/10/16 03:24 AM Re: Count Rumford [Re: logtroll]
pondering_it_all Offline
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Registered: 02/27/06
Posts: 7140
Loc: North San Diego County
I can see from the photo that the angles are not too tricky. You are just building the back as one plane and the sides as two intersecting planes. It will get a bit more custom fitted as you angle the top part of the chamber to fit the damper.

I doubt you need to slow the heat exchange between the firebricks and the back regular brick wall. The heat will move very slowly through the firebricks, which gives you good front heat efficiency. Heat that does get through could then move quickly through regular bricks to the outside. It might not even get to the outside if the outside surface of the regular bricks is cold. Adding more insulation between the firebricks and the regular bricks just lets the insulation get hot. Hope it is as heat-proof as the firebrick.

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#292356 - 09/10/16 03:29 AM Re: Count Rumford [Re: pondering_it_all]
logtroll Offline
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Registered: 04/26/10
Posts: 8647
Loc: New Mexico (not old Mexico)
The surrounding masonry is likely more than 50% air because of the high vermiculite and foam (air bubbles) content. I don't expect much heat transfer through it.
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#292358 - 09/10/16 04:49 AM Re: Count Rumford [Re: logtroll]
pondering_it_all Offline
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Registered: 02/27/06
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Loc: North San Diego County
Let us assume the heat transfer through the normal bricks is very fast. If you had just firebrick in contact with a normal brick back wall, then the back side of the firebricks would not get hot (because the heat that got there would leave very quickly out the back wall). The temperature gradient is within the firebricks.

If you have a layer of insulation between them, then the back of the firebricks will get hot. The temperature gradient will be across the insulating layer. Hopefully the insulating layer can take the heat. It is probably unimportant unless you want to run the fireplace 24/7.

One thing that makes a fireplace easier now is the use of 8"-12" round double-wall vent pipe above the damper flap. The pipe barely gets warm on the outside, so upper chimney boxes can be made of wood. Easy to retrofit such a pipe inside an old brick chimney. Much easier to clean.

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#292367 - 09/10/16 11:49 AM Re: Count Rumford [Re: pondering_it_all]
logtroll Offline
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Registered: 04/26/10
Posts: 8647
Loc: New Mexico (not old Mexico)
A flue pipe would be nice but my chimney opening is a narrow rectangle approximately 4" x 24". If this was a serious "working" heating unit I would consider rebuilding it, but it will be only getting occasional use.
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#292395 - 09/10/16 07:58 PM Re: Count Rumford [Re: logtroll]
pondering_it_all Offline
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Registered: 02/27/06
Posts: 7140
Loc: North San Diego County
Quote:
4" x 24"


Yep, you probably should just leave that the way it is, as long as the chimney bricks are okay. The vent pipe would be good if you had to rebuild the chimney, because then you could just use wood siding.

I can foresee it being a bit difficult getting that damper box on top of the firebrick. You'll have to fix it up there, then install the last bricks with some mortar on top to seal it to the bricks.

You also have to go from the herring bone pattern to straight horizontal at some point, or do a lot of fancy cuts on the top.

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