Convection Fireplace Pocket-RMH

I've done some searching and found ideas for RMH in chimnies, but I didn't find anyone using convection to help send the heat to the room. My fireplace gives me a 22" cube to work in, little extra width I can use for the infeed. My wife doesn't want to be able to see any of this, so it has to stay inside. I was thinking about using a simple J-type with a ~5 gallon bucket. Then snaking the exhaust gases through some 4" tubing and placing a fan behind all of this to blow the heat into the room. It's not a big space, do you think I can make an effective unit in this small space? I could also add some fins to the bucket to get better cooling across it. This seems very logical to me, but I'm not sure it will work as well in practice.

I am fortunate that my chimney cleanout is outside, just 6" below the fireplace, so I can run the exhaust outside easily. I will test everything outside first of course. Interested to hear the feedback.

Thanks.

pics of the fireplace please!

Your indicated 22" vertical puts a big crimp on your J stove diameter.

You might want to google up "Zero rocket" it should take you to a free .pdf around 10MB or so that might give you some ideas.

That vertical limit is a problem.