A.Stephen Bushway, mason and venting system specialist, responds: If there is one situation where you need to follow the manufacturer’s installation instructions, it is with metal fireplaces. They are sold as a system, with brand-specific chimneys. The components required will vary from manufacturer to manufacturer.

When the chimney is enclosed in a chase, some manufacturers require that the chase be equipped with two vents, one at the floor level and one near the ceiling, to help dissipate heat inside the chase. You need to install firestops at floor penetrations, where specified. Because the outside diameters of metal chimneys vary, the firestops are manufactured components specific to the type of fireplace you are installing.

Although each system varies, in many cases the installation instructions will specify requirements for wall bands to support the chimney and attic insulation shields, where applicable. Instructions should include a chart for calculating lateral distances when installing offsets and offset supports in the chimney.

Get a copy of the installation instructions before you start. This will give you the required clearances for the system, as well as information on what accessory components to order.