Mild to Severe Issues with 40 Year Old Hand Fed Furnace
Posted: Wed. Oct. 13, 2021 12:11 am
Apologies for the long post; lots of ground to cover.
I'm dealing with a mid-80s ThermoMax H624 Wood/Coal furnace, 9" flue, assorted problems and potential problems. I've been burning this for three years, and last year was BAD. I've learned a lot on this forum to make this year better, but I still have some concerns.
To begin, the furnace is obviously old, cast iron, and installed on a concrete floor in a damp basement. It's got rust issues. Most of this is surface, and the firebox is still solid, but there is at least one problem area (explained below). The flue is 26 gauge galvanized with an 8" barometric damper, total length from flue outlet to chimney interior is no more than six feet or so. It's "S" shaped (two 90 elbows facing opposite directions with a 3' section in the middle; the baro is located in this middle section). The flue also has corrosion to the point of holes, but that will be "new" by the start of this season. I'm keeping the original baro.
The shaker grate is irreparably damaged, broken in pieces and warped by the heat over time (it was like that when I acquired the house). I actually wired it together with coat hangers our first winter here, and got it to essentially function, but of course that was temporary and didn't last. The inability to effectively "shake" the fire is problem one.
The dirty, filthy, awful, run-of-mine, high volatile Pittsburgh seam bituminous coal we burn is another. Sized from massive chunks down to (entirely too many) fines.
The flue feeds into a standard brick UNLINED chimney, which was originally four 9" openings but three were "sealed" and now it is only the one. In essence, I'm only using one corner of the actual chimney. The flue literally pokes through the brick and just lays open in there. There is no chimney cap. The chimney itself is essentially solid, and I cleaned it to within an inch of its life when we first moved in (three winters ago). I'll likely do that again before this season commences. It is two stories tall, for what that's worth.
Now the issues. First, the fire won't burn consistently; it acts as if it's "wet" at times, which is ridiculous but that's the best way I can describe how it is behaving. I have not been careful to deal with fines properly (I've learned now that is a mistake) and so I consistently crusted my fire over with a hard shell as they meld together. Granted, I tend to poke holes to the bottom grate fairly regularly, but it still is often hit or miss with burning. Sometimes it will burn for a week with no issues, and sometimes I spend an hour lighting it, three times in a day. The only air inlet is a door on the below-firebox ash box, which doesn't allow for fine adjustment at all, and a minimal dial in the feed door affecting the over-fire air. I have sealed the feed door with fiberglass "rope". The ash door is not as well sealed.
I believe the draft is sufficient, and does not seem to be inconsistent. The first two years the baro seemed to do what it's supposed to, but last summer I made the mistake of cleaning and fiddling with it, and now I can't seem to get it to function at all. I'm sure it's an adjustment issue--I just am not clear what to adjust it to. Help on that would be appreciated. It is somewhat affected by rust, but I'm sure I can get the weights to adjust.
Now the heart of my issues (there are two). First--and because the fire won't burn well (and I've never had it burning super hard/super hot) I suspect this is the result--I get MASSIVE buildup of gel-like soot all through the heat exchanger and flue, bad enough that it all but completely closes off the system in a matter of 2-3 WEEKS. I will literally have to let the fire die for a day or two, completely remove the flue, and then go in by hand and remove this black jelly by hand, to the tune of two five gallon buckets, at least once per month and usually more often. This, of course, only compounds the burning problem, which compounds the soot problem, on and on. And I have to do this by sticking my arms clear into the furthest crevices of the kidney, while laying in a 2 foot space between the furnace and the chimney.
This operation revealed the second (and potentially more serious?) problem...the bottom of the kidney is almost completely rusted out. The advantage of all this soot was that it "sealed" the thing so I didn't know about it until the first time I had to do the cleaning. Anyway, it is bad enough that I had to do something (once "clean" it was pushing smoke/soot into the whole house via the ductwork and fan). Welding it in place isn't something I was able to do, and replacing the kidney (I found one for $600, which I would have had to go get and then install myself) wasn't and still isn't an option. Besides, I could replace the furnace for not much more. Instead, what I did was use the heavy-gauge sheet metal from an old shop light, bent and folded and finagled until it was approximately the right shape, cut tabs into it so it could be flexed into place over the still-solid metal of the kidney, and then stuffed any gaps that remained with stainless mesh (of the "pot scrubber" variety). This seems to have worked just fine, but I'm concerned now that it may throw off the drafting of the stove, and/or be allowing gasses to escape that I'm just not aware of but which could be a problem since they'd be going straight into the ductwork.
This second issue I'll have to find a permanent solution for; I mention it only to get any opinions as to how pressing it might be. I don't burn more than a handful of wood each year, so I'm less concerned with the risk of a chimney fire (and how such a problem might feed it). But if this could be causing drafting issues that may be giving me the bad burn, I'd like to hear opinions on that as well. I have to go with it this year in any case, so if necessary I'll find a way to patch it better.
That first issue, though--the soot--I have to find a way to mitigate. As mentioned, I'm sure all of these things inter-relate to CAUSE the soot problem, but I guess my question is--where should I start first?
I've included a picture to show what the inside of the kidney would look like if you could see it. Upper hole feeds smoke into the kidney from the firebox, with an inverted "V" of metal that sends the smoke (and sadly, soot) down to the flue and out the chimney from both sides. The red represents where the soot gathers the most, and the green is the area of the heat exchanger kidney that has rusted out (where my sheet-metal repair is).
Thank you for any comments and suggestions. Now I think I'll go lay down--I sprained something writing all of this.
PS--I really do like this furnace. The design seems good, the firebrick is all still solid and the firebox in general seems "worthy", and I would prefer not to replace it. I just want to make it work better without paying through the nose or risking it poisoning my family while they sleep.
I'm dealing with a mid-80s ThermoMax H624 Wood/Coal furnace, 9" flue, assorted problems and potential problems. I've been burning this for three years, and last year was BAD. I've learned a lot on this forum to make this year better, but I still have some concerns.
To begin, the furnace is obviously old, cast iron, and installed on a concrete floor in a damp basement. It's got rust issues. Most of this is surface, and the firebox is still solid, but there is at least one problem area (explained below). The flue is 26 gauge galvanized with an 8" barometric damper, total length from flue outlet to chimney interior is no more than six feet or so. It's "S" shaped (two 90 elbows facing opposite directions with a 3' section in the middle; the baro is located in this middle section). The flue also has corrosion to the point of holes, but that will be "new" by the start of this season. I'm keeping the original baro.
The shaker grate is irreparably damaged, broken in pieces and warped by the heat over time (it was like that when I acquired the house). I actually wired it together with coat hangers our first winter here, and got it to essentially function, but of course that was temporary and didn't last. The inability to effectively "shake" the fire is problem one.
The dirty, filthy, awful, run-of-mine, high volatile Pittsburgh seam bituminous coal we burn is another. Sized from massive chunks down to (entirely too many) fines.
The flue feeds into a standard brick UNLINED chimney, which was originally four 9" openings but three were "sealed" and now it is only the one. In essence, I'm only using one corner of the actual chimney. The flue literally pokes through the brick and just lays open in there. There is no chimney cap. The chimney itself is essentially solid, and I cleaned it to within an inch of its life when we first moved in (three winters ago). I'll likely do that again before this season commences. It is two stories tall, for what that's worth.
Now the issues. First, the fire won't burn consistently; it acts as if it's "wet" at times, which is ridiculous but that's the best way I can describe how it is behaving. I have not been careful to deal with fines properly (I've learned now that is a mistake) and so I consistently crusted my fire over with a hard shell as they meld together. Granted, I tend to poke holes to the bottom grate fairly regularly, but it still is often hit or miss with burning. Sometimes it will burn for a week with no issues, and sometimes I spend an hour lighting it, three times in a day. The only air inlet is a door on the below-firebox ash box, which doesn't allow for fine adjustment at all, and a minimal dial in the feed door affecting the over-fire air. I have sealed the feed door with fiberglass "rope". The ash door is not as well sealed.
I believe the draft is sufficient, and does not seem to be inconsistent. The first two years the baro seemed to do what it's supposed to, but last summer I made the mistake of cleaning and fiddling with it, and now I can't seem to get it to function at all. I'm sure it's an adjustment issue--I just am not clear what to adjust it to. Help on that would be appreciated. It is somewhat affected by rust, but I'm sure I can get the weights to adjust.
Now the heart of my issues (there are two). First--and because the fire won't burn well (and I've never had it burning super hard/super hot) I suspect this is the result--I get MASSIVE buildup of gel-like soot all through the heat exchanger and flue, bad enough that it all but completely closes off the system in a matter of 2-3 WEEKS. I will literally have to let the fire die for a day or two, completely remove the flue, and then go in by hand and remove this black jelly by hand, to the tune of two five gallon buckets, at least once per month and usually more often. This, of course, only compounds the burning problem, which compounds the soot problem, on and on. And I have to do this by sticking my arms clear into the furthest crevices of the kidney, while laying in a 2 foot space between the furnace and the chimney.
This operation revealed the second (and potentially more serious?) problem...the bottom of the kidney is almost completely rusted out. The advantage of all this soot was that it "sealed" the thing so I didn't know about it until the first time I had to do the cleaning. Anyway, it is bad enough that I had to do something (once "clean" it was pushing smoke/soot into the whole house via the ductwork and fan). Welding it in place isn't something I was able to do, and replacing the kidney (I found one for $600, which I would have had to go get and then install myself) wasn't and still isn't an option. Besides, I could replace the furnace for not much more. Instead, what I did was use the heavy-gauge sheet metal from an old shop light, bent and folded and finagled until it was approximately the right shape, cut tabs into it so it could be flexed into place over the still-solid metal of the kidney, and then stuffed any gaps that remained with stainless mesh (of the "pot scrubber" variety). This seems to have worked just fine, but I'm concerned now that it may throw off the drafting of the stove, and/or be allowing gasses to escape that I'm just not aware of but which could be a problem since they'd be going straight into the ductwork.
This second issue I'll have to find a permanent solution for; I mention it only to get any opinions as to how pressing it might be. I don't burn more than a handful of wood each year, so I'm less concerned with the risk of a chimney fire (and how such a problem might feed it). But if this could be causing drafting issues that may be giving me the bad burn, I'd like to hear opinions on that as well. I have to go with it this year in any case, so if necessary I'll find a way to patch it better.
That first issue, though--the soot--I have to find a way to mitigate. As mentioned, I'm sure all of these things inter-relate to CAUSE the soot problem, but I guess my question is--where should I start first?
I've included a picture to show what the inside of the kidney would look like if you could see it. Upper hole feeds smoke into the kidney from the firebox, with an inverted "V" of metal that sends the smoke (and sadly, soot) down to the flue and out the chimney from both sides. The red represents where the soot gathers the most, and the green is the area of the heat exchanger kidney that has rusted out (where my sheet-metal repair is).
Thank you for any comments and suggestions. Now I think I'll go lay down--I sprained something writing all of this.
PS--I really do like this furnace. The design seems good, the firebrick is all still solid and the firebox in general seems "worthy", and I would prefer not to replace it. I just want to make it work better without paying through the nose or risking it poisoning my family while they sleep.