Mild to Severe Issues with 40 Year Old Hand Fed Furnace

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SWPAhomestead
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Hand Fed Coal Furnace: Mid-80s Thermomax H624

Post by SWPAhomestead » 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.

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McGiever
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Post by McGiever » Wed. Oct. 13, 2021 2:07 pm

You must have properly installed working Carbon Monoxide Detectors. Are there any alternate coal suppliers you could use?

 
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Lightning
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Post by Lightning » Wed. Oct. 13, 2021 7:44 pm

Wow man.. you probably don't wanna hear this but yer really burning coal the hard way with an appliance that sounds like it's in potentially dangerous condition. You could replace it with a nice secondhand unit, burn anthracite, and make life a lot easier on yourself. Just sharing my opinion.

 
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Post by franco b » Wed. Oct. 13, 2021 8:55 pm

I agree with Lightning. You are throwing away a third of your heat as soot. To burn bit you must provide heated over fire air to control the smoke and soot.

 
SWPAhomestead
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Hand Fed Coal Furnace: Mid-80s Thermomax H624

Post by SWPAhomestead » Wed. Oct. 13, 2021 9:51 pm

Thanks to those who have posted. A replacement isn't in the cards for this season, so I'm going to have to make the best of it at least until Spring/Summer of next year.

I do have a CO2 detector operating in the upstairs living area, and test it regularly. As for suppliers, all the ones in my immediate area source from the same place, and I'm pretty well locked in to the one I have for the moment (business arrangements in which I'm carrying a credit balance with him, so he "owes" me coal).

I have burned anthracite--not especially well, mind you--but purchasing by the bag got both expensive and unwieldy. When I do change this furnace out, I may reconsider that if I can find a bulk supplier. Out of curiosity, is there any advantage/disadvantage to burning a mixture of the two? I still have a couple of bags of pea anthracite, and can always get more.

Regarding "heated" over-fire air--to what degree (pardon the pun) must the air be heated? The area of the basement where the furnace is located is always toasty when the furnace is burning, and this is obviously where it's drawing it's air supply (the "replacement" air coming from a drafty area on the other side of the basement). Should I configure some sort of forced-air system to push air over the fire? That shouldn't be too hard to do, and pre-heating should be relatively straightforward if I can draw the forced air from within the sheetmetal "heat box" that surrounds the furnace...


 
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warminmn
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Post by warminmn » Wed. Oct. 13, 2021 10:42 pm

heated air has to be preheated inside the stove, like with pipes inside the stove, or a distance from the fire itself (think air spinner on the door). Hot air ignites the gasses inside the stove. The added pipes inside will heat up that air before it reaches the fire and if done right works quite well. Door spinner maybe not as good but does work. There are a few posted topics on this site about over fire air if you search for them using the search box near upper right corner. Galvanized pipe will work, probably a pair of 1" inside diameter size minimum if you go that route. Ran along the top of your firebrick inside with holes drilled in them aiming towards the fire. Member Lightning has a post that describes the size and how many holes to drill. Maybe other posts do too.

Burning bit your chimney should be cleaned and/or checked a few times a year. Your chimneys large size has helped you in that respect. I'd get another CO detector for the basement and another one with a readout for upstairs if your going to try using that beast another year.

Switching back and forth between anthracite and bit can be done with some stoves but i'd forget about it with what your using.

 
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Post by Hambden Bob » Wed. Oct. 13, 2021 11:11 pm

Wow...I reread your entire post three times. I let it sink in. I can't help you,nor can I offer any advice other than you have to get a fully functional,non rusted out unit in place of that corroded safety hazard you're trying to claim is operable. You can't control your combustion nor draft. You are leaking CO into the house. That has to stop. As has been said,there are alot of intact units that are being sold due to conversion to Natural Gas,or Folks who have aged out and can't do Coal anymore. Your situation is dire because you've waited till now,the edge of the start of cold weather coming. If you're flat broke,and have a Family to keep Warm and Safe,We're listening. We're not the "Little Sisters Of The Poor" here,but We're listening.

 
SWPAhomestead
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Hand Fed Coal Furnace: Mid-80s Thermomax H624

Post by SWPAhomestead » Thu. Oct. 14, 2021 12:20 am

Thanks Bob (and others).

It's less about the cost (though that's not insignificant), more about the overall situation. 100 year old house we're already rehabbing as we can, limited ability to haul (you should see what we can get into a Honda Civic--but a coal furnace ain't going in there NO HOW), aging back and knees, VERY small stairwell into the VERY small door of the basement, and as you say--time not on my side. We won't freeze; we have supplemental heat all over the house. If the furnace is flat-out unsafe (and can't be made safe) I'll use the supplemental until I can get another one in here. That's the reason I posted, honestly...to find out just how dire it really may be.

The smoke intrusion stopped (as far as anything noticeable, at least) as soon as I patched up that bottom area of the kidney, and I'm terribly thorough; it's not welded or puttied or anything like that, but the patch is mounted tight and stuffed even tighter with stainless wadding. It's gas, so I'm not about to say that nothing is passing through there, but it's got to be working awfully hard to do so if it is, especially given that the chimney is drafting right above it. Still, if it's utterly unsafe, I won't bother burning it until I can get a different one.

I've done many things "wrong" when I have burned, partly out of a "wood" mentality and partly out of fear of burning too hot (which seems now to be the exact opposite of how I should be doing it). I've definitely fed improperly and failed to take into account the "fines". I haven't emptied the ash bin until it's well full (another mistake I've learned about on here). I suspect that the combination of these mistakes has led to most of my poor burn experience, and the poor burn is leading to the soot problem. Nevertheless, if I can burn perfectly but still not safely, I'll use alternative means until I have a better furnace.

 
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warminmn
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Post by warminmn » Thu. Oct. 14, 2021 9:46 am

Do you have a chimney inlet in the living area to hook too? A Warm Morning brand stove or a few other brands do not sell terribly high and burn bit coal ok. They dont weigh a ton either. One man with a 2 wheeler could move one except for steps. I took my Riteway into my house in pieces by myself to get the weight down.

You have to be more careful loading in a living area because of smoke but its manageable. many of the stoves will burn anthracite too.

 
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Post by jedneck » Thu. Oct. 14, 2021 7:05 pm

I have a ds machine riteburn taking up space in yard. Its no show queen but pretty sure its serviceable with new firebrick. It yours if want it. Just have to pick it up. I’m in central pa 30min from carlisle in perry county


 
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Post by Rob R. » Thu. Oct. 14, 2021 7:15 pm

Based on your description, the existing stove is destined for the scrapyard. Cut or break it up into manageable pieces and get it removed.

I would not burn wood with an unlined chimney, but it should be fine with anthracite, and also with bituminous if you get a stove that will allow you to burn the volatiles and minimize soot.

Does the house have any form of central heat?

 
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warminmn
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Post by warminmn » Thu. Oct. 14, 2021 8:14 pm

jedneck wrote:
Thu. Oct. 14, 2021 7:05 pm
I have a ds machine riteburn taking up space in yard. Its no show queen but pretty sure its serviceable with new firebrick. It yours if want it. Just have to pick it up. I’m in central pa 30min from carlisle in perry county
Real nice of you Jed. Would be worth a long drive for OP to get too.

 
SWPAhomestead
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Hand Fed Coal Furnace: Mid-80s Thermomax H624

Post by SWPAhomestead » Thu. Oct. 14, 2021 10:00 pm

Wow, lots of responses. I've been gone all day so I'm just now checking in.

First, Jed--thank you. That is indeed a very awesome offer, and one I'm definitely inclined to take you up on if I can arrange a truck. It would be the first of the week at the earliest. I am familiar with Perry County, so that's a plus. That particular stove is a downdraft model, yes? I've always admired the design (I even built a rocket mass heater once, which works on the same general principle). I will definitely be in touch via message.

In answer to other questions--the furnace I've described is our central heat. It's surrounded by a sheet metal box with ductwork at the top and a fan (with cold air return) at the bottom. The system is very simple but works well, and even without power it radiates heat nicely when it's burning properly. When we first moved in there was no power; I had to completely rewire from the pole on in, and everything inside the house. We went most of the winter on solar lights and purely radiant heat from the coal furnace, and still maintained mid-sixties. I guess that's why I like this thing so much; it "worked" when we needed it to.

There is no chimney access from inside the living area, though that wouldn't be hard to accomplish; the brick chimney lays behind plaster and lathe, all easily enough removed and broken through. But I'm looking to stay with the central system that is in place now. The stove Jed mentioned may not be ideal for this, but I believe that very slight modification of the sheet metal heat box would allow it to provide heat in exactly the same way the current setup does, and that's work that's easily enough done. I believe most of the firebrick I currently have is still in decent shape, but if it's not or if it isn't the right size/shape, I just priced brick at Tractor Supply and it's reasonable enough to replace.

Regarding burning wood, I only burn (literally) a shopping cart worth for the whole season, fully seasoned and all hardwood. Something about chimney fires keeps me up at night, so I stick to wood to get things started and coal from there on out. This worked well until this past season and the malignant soot problem.

Thanks to everyone who has responded. I'm learning a lot, and finding that coal people are just genuinely good folks. That doesn't surprise me; there's a certain self-sufficiency that comes with burning coal, and that's pure Americanism at it's heart. That's why we homestead, that's why I insisted on buying a home with a wood/coal furnace, and that's why we prepare for the worst. Lately that "worst" seems to be close at hand, and my faith in humanity has been pretty well tested. This board has restored some of that faith.

 
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jedneck
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Post by jedneck » Fri. Oct. 15, 2021 7:18 am

I’ll get some pictures soon as I’m home and it’s light enuf to see.

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