Fireplaces and flues
Factory-built (prefab, zero-clearance) fireplaces, the metal fireboxes framed into Portland tracts and condos
We inspect, sweep and repair factory-built fireplaces in Portland-area houses and condos, from refractory panels to the pipe, chase cover and cap. What usually fails is a rusted chase cover letting rain in, cracked refractory panels, or the wrong cap on the pipe.
Updated
What a factory-built fireplace is and how it vents
A factory-built fireplace is a listed metal firebox made in a plant, shipped with its own chimney pipe, and set into a wood-framed opening with almost no clearance to the studs, so the trade also calls it a prefab or zero-clearance unit.
It vents through a round metal chimney tested with the firebox as one listed system, either an air-cooled pipe of nested walls or a solid-pack insulated pipe, run up inside a plywood and siding chase and finished with a flat sheet metal chase cover and a round cap.
Census figures put about a third of the housing in Washington and Clackamas counties in the 1970s and 1980s, and a framed, sided chase on a split-level, a townhouse row or a condo stack from those decades is where we find these units.
How to tell what you have
Four things tell a prefab from brick before anyone climbs on the roof.
- Firebox walls made of three or four large flat panels, gray or tan, with a visible seam in each back corner instead of rows of small bricks.
- A rating plate or paper label inside the face, behind the screen or under the hood, naming the maker, the model and the pipe it was tested with.
- A thin steel damper plate in a sheet metal throat, worked by a pull chain or a short slide, not a heavy cast iron plate.
- Outside, a square chase sided to match the house, topped by a flat metal cover with a round pipe and cap poking through.
What you will find in Portland homes
The prefab units we open up around the metro fall into these groups.
| Type or model | Era | Notes |
|---|---|---|
| Radiant open-front box | Older models | Single steel firebox with a mesh curtain and air-cooled triple-wall pipe; thin panels and a rusted chase cover are the usual finds. |
| Circulating box with louvers and a blower | Earlier models | Double-wall firebox with vents above and below the opening; the fan and its wiring sit in the lower cavity, collect dust, and a stuck blower gets mistaken for a draft problem. |
| Clean-burn unit with sealed glass doors and outside air | Current models | Built to burn cleaner, with a ceramic baffle and secondary air tubes; it is swept around the baffle like a stove and the door gasket is checked. |
| Prefab with gas logs or a wood insert added | Any | Either is right only when the plate or the insert maker lists that firebox; without the match the steel box can overheat the framing, so this gets a Level 2 and a frank answer. |
What goes wrong and what fixes it
A prefab fails at its chase cover, panels, pipe and cap, and each fault below is paired with the visit that fixes it.
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Unknown condition of the pipe, panels and chase after a purchase or a chimney fire
A Level 2 camera run of the pipe, the panels checked for cracks, the plate read and the chase cover looked at from the roof Chimney Inspection, from $129
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Cracked, crumbling or missing refractory panels
Panels replaced with the maker's part or a listed universal panel cut to fit; a panel cracked through keeps the unit cold until then Smoke Chamber and Firebox Repair, from $299
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Creosote on the pipe walls and the mesh curtain or glass
A poly or wire brush sized to the pipe's inside diameter, with the spark screen and curtain cleaned Chimney Sweep, from $249
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A rusted chase cover letting rain run down the pipe and into the firebox
A new stainless cover with a drip edge and a cross break, and a storm collar sealed at the pipe Chimney Flashing and Leak Repair, from $399
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A missing or wrong cap, or a cap screen packed with debris
The listed cap for that pipe, since a masonry cap does not fit and a mismatched one chokes the draft Chimney Cap Installation, from $299
How a prefab fireplace is swept and inspected differently from brick
A prefab gets a softer brush, a closer look at the panels and a roof check of the cover, because what fails on it is thin metal and ceramic rather than brick and mortar.
The pipe is brushed with a poly or wire brush matched to its inside diameter, from the top or through the damper opening, with the face sealed and a HEPA vacuum running. A stiff masonry brush scores the inner wall of an air-cooled pipe, so it never goes in one.
Inside, we pull the grate and screen, vacuum the firebox, check every panel for cracks, chalking and open seams, and photograph the rating plate. Outside, the chase cover gets a hand on it for rust-through, pooled water and a missing cross break.
When a factory-built fireplace should be retired rather than repaired
Retire the unit when the firebox is warped or rusted through, when the pipe or the panels are no longer made for it, or when the chase has already caught fire; repair it when the panels and the cover are the whole problem.
A factory-built fireplace is a listed system, so masonry repairs do not transfer: nobody can parge a steel firebox, line an air-cooled pipe with stainless or stack brick on a chase cover. Parts have to match the plate, and a discontinued line means the unit has reached its end.
The choices from there are a new listed unit from a hearth dealer under a permit, an insert only when it is listed for that firebox, or closing the opening; our part is the inspection, the sweep and the venting checks.
A prefab that smoked into the room, showed a cracked panel or had a chimney fire stays cold until it is inspected. With a chimney fire burning, get everyone outside and call 911 before anything else; the fire department clears the house, then we look at the pipe.
Rain, chase covers and the Portland prefab
Rain is what ends a prefab in this climate, and it gets in through the chase cover before anywhere else.
A galvanized cover rusts from the top down where water pools around the pipe collar or along a seam; the first sign indoors is rusty drips on the panels or a brown ring on the hearth. Moss on the shaded side holds water against the plywood, and the fix is a stainless cover with a drip edge, a sealed storm collar and the right cap.
Factory-built fireplace questions
Can I put a wood insert into a factory-built fireplace?
Only when the insert maker lists that exact prefab firebox. A factory-built unit sits inches from framing and was tested as one system, and an insert pushes more heat into a box never rated for it. We read the plate, check the listing and give a straight answer.
How often does a factory-built fireplace need a sweep in Portland?
As needed, which for a prefab burned through a Portland winter usually works out to once a year, with the panels and cover checked each time. The pipe is narrower than a masonry flue, so creosote closes it faster, and the national standard asks for an inspection every year regardless.
Are cracked refractory panels in a factory-built fireplace really a problem?
Yes, once a crack goes through the panel or the panel crumbles at a seam. The panel is what keeps heat off the steel box and the framing behind it. We measure what we find and replace the through-cracked panels before the next fire.
Why is water dripping inside my factory-built fireplace?
Usually a rusted or flat chase cover letting rain pool around the pipe and run down it, with a missing storm collar the next suspect. The water stains the panels and leaves a brown ring on the hearth. A stainless cover with a cross break and a drip edge fixes it.
Does a factory-built fireplace count under Oregon's wood stove removal law?
No. An open factory-built fireplace with no air controls is exempt from the home-sale removal law, just as an open masonry fireplace is. The law reaches uncertified stoves and wood inserts only, so a prefab comes into it when an uncertified insert has been set into the box, and that insert is what has to go.
Related pages
Factory-built fireplace calls near you
Factory-built fireplace work has taken us to Hillsdale, Mt. Tabor, Rose City Park and the rest of the metro, and the posted price is the same at every address.
Other fireplace and flue types
Ready to book a sweep?
Call with what the fireplace is doing, or text a photo of the opening and one of the chimney top, and we will name the service and its posted price before we come out.