Masonry or Factory-Built? Gas Logs for Green Homes

Telling the Two Types Apart

A masonry fireplace is built on site from brick, block or stone, with a firebrick-lined firebox and a clay tile or masonry flue. A factory-built fireplace, often called prefab or zero-clearance, is a metal box manufactured as a unit and installed into a wood-framed chase, with a metal chimney pipe running up through the house.

Even when a factory-built unit has brick-pattern refractory panels inside and stone on the face, the clues are usually easy to spot once you know what to look for.

• Metal visible at the top edge of the opening or around the damper
• Thin refractory panels inside rather than individual firebricks
• A metal chimney cap and round or square metal flue on the roof
• A rating plate, often behind a grille below the opening or on the side of the firebox
• A chimney that runs through a framed chase rather than solid masonry

Gas Logs in a Factory-Built Fireplace

A factory-built fireplace is tested and listed as a system. Whether it can accept a gas log set, and which kind, is decided by the fireplace manufacturer, not by the log maker. The rating plate and installation manual say whether decorative gas appliances are allowed, whether vent-free logs are permitted and whether a knockout is provided for the gas line.

Many prefab units allow vented decorative logs installed per the manual. Fewer allow vent-free logs. Some do not allow gas at all. We read the plate, look up the manual if needed and only install what the listing allows. If the plate is missing or unreadable, we treat the fireplace cautiously and talk through alternatives.

Bringing Gas Into a Metal Firebox

Factory-built units usually have a designated gas line knockout on the side or bottom of the firebox. The line must enter there, through the knockout, and the opening has to be sealed with the material the manufacturer specifies. Cutting a new hole in a metal firebox can compromise its listing and the clearances to framing around it.

Green's newer homes often have the fireplace on an exterior wall or in a corner, sometimes above a finished basement. We route the gas line from the existing piping, keep it accessible for future service and finish with a key valve or a control valve with a separate shutoff. If the run is long or the piping needs updating, our Green natural gas line installers cover it.

Masonry Fireplaces in Older Green Homes

Older farmhouses and earlier subdivisions in Green are more likely to have true masonry fireplaces. These follow the more familiar path: chimney sweep and inspection, gas line through a sleeve in the firebox wall, damper clamp on vented sets, and a log set sized to the firebox. Masonry fireplaces generally accept both vented and vent-free sets, provided the vent-free set is listed for a solid-fuel fireplace and the room is large enough.

Alternatives When Logs Aren't Allowed

If your factory-built fireplace is not listed for gas, there are still options. Some homeowners replace the prefab unit with a new gas fireplace designed for the space, which is a bigger project covered on our Green gas fireplace page. Others keep burning wood or use the opening decoratively.

We will tell you plainly what your fireplace can and cannot take. For more on log materials, burners and ignition, see our Stark County gas log guide, and ask about our Green plumbing maintenance if you want the set checked yearly.