With winter approaching, I'm once again dreaming about what to do with my fireplace. For several winters I've considered what to do.

The house was built in 1948, and the fireplace is a 5' wide masonry with a steel double wall passive heatilator-style insert. At face value, everything is in great shape and still solid after all these years. 12x12 tile flue in excellent shape. No issues with fireplace (good draft, etc), except the lack of efficiency. Growing up with a wood stove cranked every weekend leaves me wanting more.

With no room in the house to put in a freestanding unit, are there safe, intended products for use in this type of situation? Many warn against inserts going into pre-fab fireplaces, but most of the products out there indicate use in both pre-fab/masonry/any type of existing fireplace. I'm not sure if those warnings are for the zero clearance "sheet metal" type fireplaces with 2x4 framing mere inches from the fire or not...

In my situation, are there any reasons not to put an insert in? I know specifically I have will have code issues to combustible materials (tongue and groove knotty pine over masonry to w/in 6" of opening) that I would need to rectify, as well as probably running a stainless flue liner.

Any solid models to look at?

A call to my local inspector didn't yield much insight outside of "boy, those inserts really crank out some heat!" and the local retailers/installers will sell me anything.