How are fireplace inserts installed ? Are they efficient ??

It would depend on a number of things. How big your flu is, the actual fireplace opening is, and the amount of draw on the flu as well. If you leave your damper open or partially open you'll lose a fair portion of your heating costs up the chimney. We have a fireplace insert which I like a lot. However, you lose a bit of the ambiance that a nice open fireplace offers. We have a fan that we turn on that blows the hot air into the house which is beautiful. I guess it boils down to how much your pocket book can stand to pay for heating costs:>
If it is a wood burning insert it will put out more heat than without one especially if it has cast iron doors on it...
They measure the inside of your fireplace and then they insert the stove ( thats all an insert is) into the fireplace. It is sealed all around and is made to blow the heat through several channels and into the room. It may not be the best lookiung thing but after getting your heating bill you forget what it looks like. I used mine from the yime I got up in the morning and filled it with wood and shut it down where it still burned. When I got home from work I would fire it up again. I got most of my wood for nothing as I worked near a Pallett repair shop and collected all the scraps and waste. Most of the wood was hickory, maple or oak. I would say I saved over 40% on my oil