NG Furnace getting long in the tooth

Hoping a moderator (or senior contributor) can point me to a couple thread(s). My Trane NG forced air furnace is 15 years old - been throwing some interesting controller codes. Welp, this will be my opportunity to look at something wood fired (in tandem) for the basement - so can you point me in the right direction. Sorry I don't have the bucks for a gasifier unless they've gotten a lot cheaper past 5 years.

My Hampton insert on the 1st floor keeps us cozy in the front living room, but it's certainly not doing the heavy lifting of keeping the house warm below 20F.

Many thanks and happy holidays,
Churchie

Thanks for the replies I'll check out the gasifier link later. I have a 100k BTU Trane NG single stage forced air furnace, model number TUC100C948B7 serial number R364M7S7G. The "R" (from Googling) indicates manufactured year 2000. Recent fault has been '4 flashes' described as 'Open High Limit Device'. After a bit of head scratching and two evaluations from Service Technicians the fault has gone away (for now). Yes, NG is cheap here in NE Ohio, will stay cheap and I always planned on replacing NG furnace with another NG furnace. Usually what goes on these is the blower, and it's just better off buying a new furnace at that point. Just wondered if there was any sense in placing a wood fired furnace in line (think I've seen someone talk about their Caddy Furnace years ago).

Really like my Hampton. It's installed to a large outside chimney and also near the main staircase. So supplemental heat is an accurate description of its limit.

Well that is two mentions of Kuuma, never heard of that brand and I've been reading posts on Hearth for quite a few years. I just sent them an email for information. I'll also search on this forum. My NG furnace uses PVC piping to vent out side of house. The central chimney flue, right next to the NG furnace, has an available flue.

I agree with balancing the $$$s. Quite a range of consideration just for a NG furnace: one can pay $5k+ for a top of the line 98% AFUE modulating NG; or, they can pay $2,500 for a basic 80% AFUE. If the gasifier break even point is no more than 10 years, in my mind it's worth it. Lots of numbers to jot down and muse over.