Retrofit Cat + Next Steps

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


New Member
Dec 20, 2021
Hello all. I've been burning as my primary heat for about 8 years; just moved to Michigan and have started here. Got an Ashley 3200 and have to heat ~3k sq ft. So far down to 20F or so it's been doing fine, though it's a little slow to get the job done being in the basement. The flue is ~25ft; with 3 stacked liners or so (18", 12", 6"?) inside one of those wood chimney add-on things, rather than a masonry chimney. I had the Fresh Air Kit installed.

After a month or so of heating with that and knowing it's going to get colder I've been looking at increasing the heat production a bit. My first mod was an accidental find with "StoveCat" - somehow I found the "retofit catalytic converters" portion of the internet and I decided that <10% of the stove's cost thrown at a gadget wouldn't be the worst thing I've ever done. Not to advertise too much; but they don't have the downsides of a normal cat in that they don't need maintenance or fuss with smoke-chamber swapping. The biggest reason I got one is that with a long flue I was concerned about creosote from burning ~4-6 months; and really don't want to clean mid season.

Note: I did an initial creosote check when I installed the cat and the stove pipe/first 6+ feet of liner seem to be sooty but nothing resembling creosote. Didn't check the top of the chimney.

The results after a couple weeks are interesting:
  • The Cat seems to increase the draft substantially. When the stove is turned all the way down I still get stove-top temps for the first hour or so of a new pile of wood in the 900+ zone -> e.g. wasted heat is my understanding.
  • Whether it's giving me extra heat or helping me build fires better; I've been keeping an extra degree or so at night and gaining an extra degree or so in the day; so despite the inefficiency of the overheat portion of the burn, it seems that my overall efficiency has gone up somewhat.
  • Stove start up to get to no-smoke (so I can go do something else) seems faster; as it should since the cat should activate around 650 smoke temp regardless of if the stove's hot enough for secondary air (the StoveCat activates at 650, I can't speak to regular cats.)
So while this is probably not the intended purpose of the retrofit (an EPA secondary air stove) I'm pretty happy with it. That said, I'm an engineer and just smart enough to be dangerous; time to crank a few more BTUs!

Here are my questions:

  • I'm considering the oft-discussed Magic Heat reclaimer; because the Cat + secondary burn gives me pretty high flue temps (initial temps are 650 to light the cat, and it burns at a similar rate down to 330 input temp.) My main concern, as it should be, would be creosote formation but I figure that between secondary burn + cat that not only are temps high enough but that there's basically no smoke left to cause issues. Any thoughts on that?

  • I'm debating adding a flue-damper. With the primary/secondary air pulls on the stove all the way out, the stove still gets to that "overheat" zone of 700+; I think getting a damper would let me stay in the goldylocks zone of 650-700 for the initial couple hours by placing it above the cat and slowing things down. This is both a safety consideration as well as an efficiency consideration.

  • I can't find any information on creosote formation regarding coals. I assume that creosote formation mostly occurs during the smokey parts of the burn and that by the time you're down to 3-400 degrees (stove top) and just coals that it doesn't matter if you have a heat-reclaimer at that point?
So any thoughts from a safety or efficiency perspective would be great, thanks!