Metal sleeves are the easiest to install, certainly more so than tiles in an existing chimney. Poured-in cement liners – cast in place – are an option, too, and last about 50 years. I’m not sure of the price.
The Hearth, Patio and Barbecue Association says a fireplace insert needs to be placed in an existing masonry or factory-built fireplace with a working chimney. A fireplace insert is either vented through a working chimney, direct vented, or vent-free, depending on fuel choice.
In most cases, a chimney liner is required. The type and size is specific to the fuel.
Vent-less gas inserts or logs come with carbon monoxide and oxygen-depletion sensors that automatically shut off if there is an operation problem.
Some municipalities have rules against vent-less fireplaces, though, so you will need to check with the building department before you proceed.
Older fireplaces lose a lot of heat. The association rates older fireplaces’ efficiency at 5 percent to 10 percent.
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