A fireplace heat exchanger works by drawing in cool air from the home and heating the air before discharging it into the home as hot air. There are two different ways to upgrade an open fireplace to use heat exchangers.
Fireplaces vary as far as efficiency, but most are in the minus 20 percent to plus 10 to 20 percent. This means most of the heat is going up the chimney, instead of into the home.
The tubular grate type is made up of a series of steel tubes that are curved to go around or behind the fire and then exit out of the top. A blower fan is used to draw in cool air from the bottom and blow hot air out the top into the home. It is important when buying these types that the steel tubes be high-quality and able to handle the high temperature and corrosive effects of a fire. This type of upgrade can be done for less than $1,000. The cost is usually around $400 to $500 for a quality-made product that lasts.
One can also buy inserts which are basically metal boxes that fit into existing fireplaces. The inserts have heat exchange chambers built into them and usually have glass doors so the fireplace does not pull in cool air, which would force the heat up the chimney, according to HowStuffWorks. These types are a lot more expensive and require a steel flume, which could mean having to install a new flume. A person can expect to spend thousands if going with the insert.