Hi. I'm new to fireplaces and I'd like to ask a few questions that I haven't found the answers to. I've been told that the standard masonry fireplace is actually not good for heating the house because you use the warm air from inside the house to feed the fire... Are there any ways to modify the fireplace to use outside (cold) air to feed the fire? I'm thinking knock a few bricks outta the back or sides of the fireplace. Even if I solve the oxygen issue. There is very little heat transfer from the fireplace to the rest of the house. I've got the crappy glass doors on the front of the fireplace and the brick hearth of the fireplace for radiation and convection heat transfer. I can add to this by getting a fireplace insert. Those things go for a couple grand at the local Ace, I'm going to go used. I figure it's cast iron, nothing to wear out with use. What measurements do I need to go by to get one? I can't find a standard fireplace size anywhere... Are these things custom built for each fireplace they go in, or are they adjustable?