The new stoves are engineered to EPA standards. You don't just put some pipes in the stove and think it's better. These stoves have a secondary combustion that ignites the smoke (unburned gas) before it enters the chimney. The opening is also smaller. Today's stoves have 6" outlets as opposed to the 8" outlets of yore. You have a "Smoke Dragon" and it's time to replace it with the newer 80% efficient stove inserts. Your stove has served you faithfully. It's time to retire it.

I'm an actual user. I live in a coastal city, and bought a townhome with an Empire Mantis fireplace. Many of my neighbours have had issues with theirs, and mine has quit operating completely - this is after extending its life a little with a brand new motherboard. While these units have been touted for being very good at heating a space, and being efficient, I can corroborate reports that the units are very noisy and problematic (e.g., the water pump failed resulting in a great deal of moisture leaking beneath my floor, damaging the wood). Empire provided a little support in early days, but have since stopped manufacturing these units and their parts. Few service centres are willing to work on these units, so we're looking at options for replacement.

If you aim for a serious amount of heat, you need to get a direct vent insert. These cost at least $2K. They are energy efficient in that most of the heat does not go up the chimney like the typical gas logs that look nice but do not give out real heat. And stay away from unvented systems which are a safey hazard and outlawed in many places. Do a search of direct vent on this forum to find out more.

Since there have been no replies to your message to date, I would suggest that you google humidifiers, find a manufacturer that has a customer service phone number and call them. That is, if you can't find a source for information locally.