I've recently begun revisiting using the fireplace in my house, which is located in an addition that protrudes 18 feet off the rear of the 2 story portion of my home. It is a fairly well constructed masonry fireplace built at an angle in the far corner of the room that is extended by the addition, the underside of which is not insulated and the ceiling is vaulted making the whole room very difficult to heat with the installed supplemental electric heat. My grandparents rarely used the fireplace in their tenure in the home due to various breathing issues in their golden years, but the price of oil has me looking for a solution to at least supplement the existing oil fired forced air. The addition was built in the 80's and the fireplace and chimney are in good shape (perhaps a good cleaning is in order) with no real damage, and from reading and research I've decided that an insert is most likely the safest and cleanest way to bring it back to life. I am considering a few possible solutions to the loss issues created by the fact the addition was built on top of some large pilings instead of a foundation by undermining and creating a crawlspace, and perhaps lowering the ceiling and increasing the insulation as well, but the most perplexing part so far comes from my research on the various inserts available. The majority of the ones I've researched state that the minimum chimney height should be 15'. on this I am assuming they measure chimney height from the top of the appliance, not the hearth? Either way the chimney is not the required 15 feet. from the hearth it is 8 feet inside (including the assumed portion within the roof), and 5 feet outside for a total of 13 ft. if you deduct the appliance height from that, it obviously falls well below the minimum chimney height specification. In addition to that I measured from the chimney to the house's second story portion and with the large soffit that overhangs, it is hardly the required 10 foot distance diagonally, but scrapes by if you measure directly to the wall. In many of the drawings I have seen, they specifically label such an arrangement as less then ideal for draft. I have found a chimney extension at extendaflue.com that appears to be a neat and easy (also cheaper then a mason) solution to extending the chimney roughly 4 feet on a 12" x 12" flue. I'm not sure if in conjunction with installing a new stainless liner this is a good/safe way to go? This extension looks like it is of good quality. The other issue I have come across, is on the inside of the front of the fireplace, at the front of the hearth, with a significant protrusion at an angle, is a cast iron air intake vent. the vent runs almost the entire length of the inside of the fireplace, and would interfere with any insert laid directly on the inside of the fireplace floor. With that said, i really like the clean look on an insert that has a shroud around it, but I'm not sure what to do to deal with this vent. Being the house is fairly tight, and the chimney is where it is located and not very long, as well as possibly being code required, It seems like having an intake is a good idea, but I cant see how it won't interfere with most inserts that have a fan located at the bottom, either from combating the output of the fan, reducing the intake capability by enclosing it or blowing on it with the fan, or just obstructing it with the insert in general. The hearth is also exactly 16", which would make coming out of the fireplace any farther then the face of it require some more modifications. Any ideas or product recommendations on this would be greatly appreciated. The last concern I have, when installing the chimney liner, the damper is undoubtedly less then 6" which is what most appliances i was looking at require, is using an oval liner acceptable, maybe just in the area that goes through the damper? Cut the metal and knock out a little brick? I am not in a position right now to take a few pictures of the situations, but I could if need be to better understand anything. Any help would be greatly appreciated. I'm Looking forward to participating in such a great resource for fireplace information.