A fireplace insert is like a wood stove that has been modified by its manufacturer to fit within the firebox of a masonry fireplace. Wood fireplace inserts are used to convert masonry fireplaces, which are inefficient and polluting, into effective heating systems. An insert consists of a firebox surrounded by a steel shell. Air from the room flows between the firebox and shell to be warmed.
The outer shell ensures that most of the heat from the firebox is delivered to the room instead of being released into the masonry structure. A decorative faceplate covers the space between the insert body and the opening of the fireplace.
Back in the early 1980s when wood fireplace inserts were first installed, they had a bad reputation for being unsafe, inefficient and expensive to maintain. Most inserts were not connected directly to the fireplace chimney and, in fact, many older insert installations allowed the exhaust gases to exit the flue collar and find their way up the chimney.
Later, a short length of stainless steel liner was installed up into the chimney of the original fireplace. This short length was called a ‘direct connect’, but there was not really a connection to the base of the fireplace chimney. Inserts installed this way were fussy to light, smoky to use and costly to maintain because the insert had to be removed to clean the chimney.
A good insert installation should be considered permanent. Installed correctly, the insert should not need to be removed from the fireplace for many years because the liner and all the hardware supporting it is corrosion-resistant stainless steel. Where the liner passes through the fireplace throat, it should be sealed to the masonry. A good seal in this location prevents cold, smelly air around the liner from migrating into the room.
An insert with a full chimney liner. Note that masonry material has been removed from the throat area and smoke shelf to allow the liner to curve gently before rising straight up through the chimney. If you already have an insert installed in a masonry fireplace, the addition of a stainless steel chimney liner can improve performance.
This improvement in the design of insert installations has improved their performance to the extent that today’s best fireplace inserts can be almost as efficient as free-standing wood stoves. Don’t make the mistake of thinking that installing an insert is a simple matter of running a liner up the chimney. Contract with the most experienced insert installer you can find. You won’t regret the small additional cost.