Mini Caddy Firebox has 2" crack- repair?

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New Member
Jul 8, 2015
Charlevoix Michigan

Back in 2009 with the help of many on this site I purchased a Mini Caddy. We've been happy with the furnace but this past season we developed an issue with the firebox near the door. A 2" inch crack has started from top left corner of the door extending outward to the left. Its out of the warranty period. The manufacturer says to seal the crack to prevent air into the combustion chamber. Makes sense And they suggest welding. Now in doing some research I've learned that there are other potentially better solutions like, brazing, patch, furnace cement and hi-temp sealants. All have their pros and cons. I would greatly appreciate suggestions on the best way to repair the crack. Picts are attached.



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Howdy DK! Man, seems SBI has had a rough run with cracks lately. The Tundra/Heatmax, which is a big box store version of the full size Caddy furnace, turned out to be a real "crack ho" about two years after they came out (2012 IIRC) Your pics look very similar to the ones I have seen on the Tundras (looks like a similar design firebox) Anyways, I bought a used Tundra that had cracked just to play with. My plan was to drill a ~1/8" hole just out past the end of the crack, this should stop it. At that point you could either air seal it with high temp silicone or stove cement. You could weld it up if you want but as long as the hole stops it, you really wouldn't need to. Welding can cause a whole new set of issues if not done correctly.
I decided to do nothing with mine except for add some heat shielding inside to the front of the firebox to see if the cracks would stop on their own before I drill holes. Funny thing is, after I made elaborate stainless steel heat shields with high temp ceramic insulation behind them, then SBI comes out with the new updated Tundras recently, they did the same thing, only with some simple firebricks cut to fit ;em DUH! Point is, don't make things more complicated than they need to be (like me) ;lol
If you want to read about the Tundra issue, here's a link
The crack issue pops up around the bottom of page 3, the shield I made, and the shields that others have made, are pictured starting around page 15 and beyond.

EDIT: You said that you are out of warranty, the Mini doesn't have lifetime firebox warranty like the Tundras?
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Welcome, DKHarwood,
Sorry to hear about your mini Caddy. I don't have one and I've never seen one in person, but I imagine it's similar to my Tundra (same manufacturer). A lot of us have had cracking problems with our Tundras that look similar to your crack. If you search in the boiler forum, you'll see a thread for "Everything Drolet Tundra/Heatmax" in which many of us discuss our cracks, and what to do about them. You might find some good ideas there.

As for me, I added firebrick to the inside front of the firebox, which I think should reduce thermal stress that I suppose caused and perpetuates the cracks. I'm going to see if that stops the cracks. If so, I'll probably avoid welding it and I might just put some furnace cement on the crack to prevent air passage, although warm temps close my crack so I'm not too worried about air.

Some of us are also adding better temperature controls to limit thermal stresses, although I assume the mini Caddy has better temp control to help avoid problems.

I honestly am not familiar enough with the mini Caddy to know if this can help your situation, but it's something to consider.

@brenndatomu and @laynes69 and others that I'm forgetting may have good ideas on the Caddy line.
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I'm not too familiar with the Mini Caddy's, but it looks like the same type of setup as the Tundra's. No false front to cool with the blower, and it's unprotected. I'm suprised it's not covered under warranty? I would do as mentioned and drill a hole and weld the crack. All these furnaces burn at very high temperatures, and not to protect the face of the firebox is asking for trouble. Our old furnace had the same cracks around a couple corners of the opening, and they never got worse in the last 5 years we burned the furnace. That furnace however was around 25 years old. I forgot to add, I would place a couple firebrick at the face to protect things. I would say, this doesn't mean they all will do the same thing, but there's alot of variables with heating demand and operation. To the OP, what size of home were you heating with the Mini caddy?
Guys, thanks for the responses. Yeh, I forgot about brother/sister furnaces under sbi. I'll review those posts, but the triangulation factor is pointing toward stopping the crack and sealing as opposed to welding. Funny thing is the old farmer I bought the house from had a look and suggested sealant and a heat shield of some sort. Not being a furnace guy but a backyard machinist out of necessity he wasn't far off. He mentioned ceramic fabric as a shield. Another option I guess. The mini is heating a 1200 sq ft ranch, but a recent addition will have us stepping up to something bigger next year, but that's for another post.
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