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...

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