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Bed Rock 11-28-2010 06:03 PM

Making an old fireplace insert more efficient
I have an old non-EPA certified Colony Hearth Earth Stove fireplace insert (at least I am sure it does not meet current EPA Phase II standards for emissions.) Rather than spend $2,000 to $3,000 for a new efficient stove, I would like to be able to upgrade this old stove and make it more efficient. I am most interested in making the stove more efficient, in terms of BTU output per unit of firewood. But since clean burning seems to be directly proportional to energy efficiency, according to one EPA study I found on line, making it more efficient would also make it cleaner.

This insert (ser. no. OCIA 060L, as far as I can tell) was manufactured by Earth Stove Northwest in Tualatin, Oregon--not far from Portland--but the company seems to no longer exist. I found a web site on the internet:, but that leads straight to the Lennox web site, a company which makes heating and cooling products. This implies that Lennox may have bought out Earth Stove. And the telephone number found on the Web: (503) 692-3991, has been disconnected. So no help from that side. I had wanted to talk with Earth Stove people to see what modifications of the original design they might have made to keep up with improved EPA standards for emissions. I had also wanted to see if they might have a glass door that would fit on my stove, which doesn't have one.

In wading through a lot sites relating to fireplace inserts, and in looking at the efficient stoves now being sold in show rooms, I found two diagrams of more efficient designs shat show a baffle above the firebox, between it and the exhaust outlet--apparently to keep the wood gases circulating within the stove longer in order to burn more completely. Such a baffle would probably not be too difficult to make and have welded into the stove. What seems more difficult to replicate, however, are tubes with holes in them at the top of the firebox, under the baffle, to allow some mixing of fresh air with the burning gases to facilitate more complete combustion. I wouldn't know just where to place these tubes, how many to use, how large the holes in them should be, and how to feed the fresh air into them. Can anyone help with this?

At present the stove exhausts into an old brick chimney. I am told it would be considerably more efficient to have the wood smoke exhaust into a chimney liner, but I am reluctant to cut out or knock out the old damper/flue which does still work well. I am wondering if a sort of manifold exists or could be created to go from the stove (the exit is about 15.5" by 3.5") through the damper/flue (which when opened is about 35" by 3") and then into a six or eight inch pipe up the chimney. (I am told that for modern commercial installations, they use stainless steel, 24 gauge pipe.) There is also the question of what kind of cap to use on the top, at the chimney outlet. But the main problem is how to get through the damper/flue.

Ideas and comments would be welcome.

Daniel Holzman 11-28-2010 06:57 PM

I have a recently constructed Jotul fireplace insert. As you noted, this insert comes with a secondary combustion system, which is the horizontal pipe near the top of the firebox with holes in it. The purpose of this pipe is to allow secondary combustion of the gases which come off the wood, which in fact increases efficiency and reduces particulate emission. As to how Jotul came up with their design, I assume there was a lot of engineering that went into the system, not something I would care to guess at. The engineering would include the size of the pipe, the size of the holes, the placement of the holes, and the connection to the air inlet system.

The actual efficiency of a stove or fireplace insert is driven by thermodynamics, which sets a MAXIMUM efficiency of a stove at (T1 - T2)/T1, where T1 is the absolute temperature of the gas within the chamber, and T2 is the exhaust temperature. As you can see from the equation, the hotter you burn, and the cooler you exhaust, the higher the efficiency.

There is a minimum outlet temperature you must maintain when burning wood, else you get creosote. Most stoves set the outlet temperatures somewhere around 500 degrees F (use temperature 957 degrees Rankine for efficiency computations). The maximum burn temperature is not much greater than 1200 degrees F (1670 R). This limits efficiency to around 45 percent, however actual efficiency is lower since there is a considerable amount of water created during burning, the heat of fusion of which is lost since wood stoves are not condensing furnaces.

The most important ways to maximize efficiency of a wood stove are :

1. maximize burn temperature by controlling the air/fuel ratio

2. Minimize generation of water vapor by burning dry wood

3. Use secondary air to burn the volatile gases. Failure to burn these gases increases pollution, and wastes energy by reducing burn temperature.

4. control heat loss out of the firebox by insulating the firebox. This helps to maximize burn temperature.

roger erickson 10-10-2012 05:39 PM

colony hearth
my name is roger, and I am a new member, I read your thread on colony hearth fireplace inserts of 2010, hope you are still reading this stuff, looks to me like you and I have the same model, I think my model number is or was C-200 something like that, anyhow, the biggest thing I am interested in and hope you may be of help, if getting a replacement for the opening, as there is no window at all, I have made inquiries into finding some sort of welder to do the job, but that seems kind of futile, have you had anyluck with finding a way to get a window, or did you ever find a replacement for that part of it, let me know, thanks. Anything of interest about old earth stone northwest will be appreciated,
Roger d erickson
silvercreek, wa

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