I have recently purchased a home which has three fireplaces in it. This is a tri-level house and about 3200 sg ft. One fireplace is located on each level with the top and bottom floor chimney sealed due to chimney liner issues. ( I had them inspected and found the middle chimney to be OK to use.) The fireplaces are located on a inside wall. I am aware that a fireplace produces the least amount of heat to be used inside as most all of the heat is drawn up the chimney. My has a 12 X 12 liner. My intent is to purchase an insert but can not do so at the present time, money! This fireplace is about 30 years old and was built on a Heat-a-lator or Vestal spec. (I am aware another company made these units but have not found out any info) Four vents are located on the field stone surface, two at the bottom one on each side and two at the top one on each side. When I have experimented, I have found by building a fire up against the metal in the back produces over time a warm air flow from the top vents. I have tried to supplement this flow by using a small fan blowing into the lower vents only to see a slight increase in are movement. My question, has anyone build a "homemade" heat exchanger to use to get more heat off the fire? I have looked at various ones on the internet ranging in price from $500 to $1500. Almost the cost of purchasing an insert. Any thoughts?