Superior RD-36 Fireplace Doors — Measure First, Order Once
Before Anything Else, Take These Three Numbers
Put the catalogs away and pick up a tape measure. To build replacement doors for a Superior RD-36, we need three things from you: the width of the firebox opening, its height, and a note about anything that intrudes into that space — a screen track, the lip of a bent louver, a gas valve key. Tape the width at the top, the middle, and the bottom of the opening. Tape the height at the left edge, the center, and the right edge. Six readings, one flashlight, about five minutes.
Why lead with the tape instead of the model number? Because after three or four decades of heat cycling, settling framing, and whatever a previous owner did to the surround, no two RD-36 openings measure alike. The tape reports what your fireplace is today; the model number only reports what it was in the showroom. Our illustrated measuring guide shows exactly where each reading lands on a louvered prefab face — bring a helper to hold the light and it goes twice as fast.
For a sanity check only: aftermarket fitment charts place the RD-36 opening near 36 inches wide by 20-1/8 inches tall. If your numbers land wildly far from that, re-measure or send us photos. If they land close but not exact, trust your tape — that small gap is precisely why doors get custom built.
Radiant or Circulating? What the RD Label Won't Tell You
Plenty of owners assume the R in RD-36 stands for radiant. The paper trail is messier than the folklore: in the Lennox-era parts catalog, the RD36 and the related RDI36 appear under the Merit Series as heat-circulating wood-burning fireplaces. So skip the alphabet theories and read the firebox in front of you instead.
The check takes ten seconds. Functional louvered grilles above and below the opening — the kind that pass room air around a double-wall firebox — indicate circulating construction, the same architecture we cover in depth on our Superior BC-36 page. A smooth face without working grilles burns as a radiant unit. For door fit, the distinction boils down to a single rule: any grille your firebox has must stay uncovered. An inside-fit frame, which seats within the opening rather than lying across the face, obeys that rule by design — and it is the only style we build for this platform.
Pinning Down Your Exact Model
Every Superior prefab carries a riveted metal rating plate inside the firebox. Sweep out the ash, angle a flashlight along the side walls or behind the lower grille, and read it. RD36 and RDI36 both belong on this page. So do plates that say Lennox instead of Superior: the brand operated under Lennox Hearth Products from 1998 until 2012, when a merger created Innovative Hearth Products — same firebox, different badge. Aftermarket door listings have long grouped the RD-36 with the rest of Superior's 36-inch platform — BC36, BC36I, BR36, BR36I, BRI36, HC36, BBV36 — because those models shared a door footprint.
Plate missing or baked beyond legibility? Photograph the fireplace and run it through our AI Fireplace Expert; identification takes about fifteen seconds. Our doors-by-model index maps the full Superior lineup — including the larger RD-42 — in case the plate surprises you.
The Factory-Door Dead End
There is no OEM counter to walk up to. Lennox Industries bought Superior Fireplace Company in 1998; in 2012, Lennox Hearth Products merged with FMI Products to become Innovative Hearth Products, which revived Superior as a brand for new fireplaces — not as a parts program for 1980s fireboxes. The generic "fits RD36" door sets still circulating online carry a warning in their own fine print: they only work if your original factory tracks and clips are present and intact. On a firebox this age, that is a gamble. A door built to your measurements mounts on its own hardware and skips the gamble entirely.
From Six Readings to a Finished Door
- Measure. Six readings plus obstruction notes, following the guide above.
- Configure. Enter your numbers in the prefab door collection, pick frame finish, mesh, and glass, and watch the price update as you go. Custom doors start at $595, and the figure on screen is the figure you pay — no quote requests, no callbacks.
- Verify. Under the Perfect Fit Guarantee, we review your measurements with you before fabrication starts, so an odd reading gets caught while it still costs nothing.
- Receive. Your door is fabricated to the 1/8 inch against verified numbers and ships free anywhere in the US.
RD-36 Measurement and Fit Questions
My three width readings don't match. Which one counts?
Report all three — never average them, never round them. Old fireboxes rack slightly as framing settles, so a quarter-inch spread between top and bottom width is common and harmless. An inside-fit frame is sized against the governing dimension so it seats cleanly at the tightest point, and the measurement review is where we settle any reading that looks off.
Do I measure the metal opening or the tile around it?
The metal. Your door seats inside the firebox opening itself, so the tape goes edge-to-edge on the steel — not across the tile, brick, or marble facing that surrounds it. That said, tell us how far any facing overhangs the opening: a proud edge of stone can affect how the frame sits, and catching that kind of detail is exactly what the verification step is for.
Can I skip measuring and copy the dimensions of my old door?
Please don't. Original doors were routinely shimmed, bent, or trimmed during installation, and forty heating seasons warp aluminum frames further. Measuring a distorted door bakes its distortion into your new one. Measure the opening — it takes five minutes, and it is the surface your new frame actually has to fit.
Tape First. Everything Else Follows.
Grab your six readings and price your RD-36 doors in the prefab door collection right now — or, if you would rather confirm the model first, send one photo to the AI Fireplace Expert and let it do the identifying. Either path ends the same way: a door built to the 1/8 inch for the opening you actually have, verified before fabrication and shipped free to your door.
More Superior models we build doors for: BR-36 · BC-36 · HC-36 · BR-42 · BC-42 · RD-42 · HC-42 · BBV-42 · EST-48 · LBR-4324 · LBC-4324 · SUPERIOR-WRT3036 · SUPERIOR-WRT3042 · SUPERIOR-WRT2036 · SUPERIOR-WRT2042 · LENNOX-LBR-3824 · LENNOX-LBC-3824 · all fireplace models