Monessen Attribute ACUF36 36" Vent Free Gas Firebox
Zero clearance to combustibles at the back, sides, top and floor — no chimney, no vent run. The Monessen Attribute 36 (ACUF36) is the enclosure half of a vent-free fireplace: a 36" x 27" clean-face opening in a 42" W x 34" H x 20" D heat-circulating firebox, listed to CSA/ANSI Z21.91 to host any listed vent-free gas log heater up to 40,000 BTU/hr, sold separately. Reversible fiber panels come standard in Multitonal Brown or Multitonal Gray, the hood and mesh firescreens ship in the carton, and a junction box is built in for a blower or light kit. from $949.
Choose the Attribute 36 if you want a built-in fireplace opening where a chimney or vent run is impossible or too costly — it frames into a 42-1/2" x 34-1/4" x 19-3/4" rough opening, straight or in a corner, sits directly on an ordinary combustible floor, and takes the 24" and 30" vent-free log sets you pick separately. Its adjustable floor supports are made for heavy concrete log sets, and the angled box pushes more of the heat forward. Optional mesh cabinet doors (ASD-36) fit this size.
It is not right for a bathroom, or for a bedroom unless the heater you put in it is rated 10,000 BTU/hr or less — those limits come with any unvented gas heater. It is not a primary heat source, it burns room air and adds moisture to the room, so a very tightly sealed house that cannot spare combustion air or add mechanical ventilation is the wrong home for it. It is also not a wood-burning fireplace and never takes a vented log set: if you want to burn wood or vent the flame outside, look at a direct-vent or wood fireplace instead.
Specifications
Frame a rough opening 42-1/2" wide by 34-1/4" high by 19-3/4" deep — add 1/2" to the width and 1/4" to the height if the trim kit will finish a cabinet or built-in; corner framing is tabled in Figure 3.3 on page 8 of the installation manual. The firebox itself is 42" wide across the face, 31-1/8" at the back, 34" high and 20" deep, and weighs 70 lb. The floor inside measures 32-7/8" across the front, 15" deep and 24-3/8" across the back, with 25-1/2" of height at the front and 22-5/8" at the back — the figures Monessen publishes for sizing a log set. Clearance to combustibles is 0" at the back, sides, top and bottom; keep 9" from the opening to a perpendicular side wall, 42" from the opening to the ceiling, and 36" from the front to anything flammable. Combustible mantel and mantel-leg clearances depend on how far the mantel projects — see Figures 7.1 through 7.4 on pages 18 and 19 of the installation manual. Non-combustible facing up to 4 inches thick may cover the metal front faces. The gas line enters through side or bottom knockouts; the junction box takes unswitched 110-120 VAC when the log set or an accessory needs it.
How the Attribute 36 compares to the 32 and 42
The three Attribute sizes share the same 27"-tall opening, 34" height, 20" depth, reversible panel choices and accessory list; they differ in width. This 36" gives a 36"-wide opening in a 42"-wide firebox at from $949; the 32" narrows the opening to 32" in a 38"-wide box at from $879, and the 42" widens it to 42" in a 48"-wide box at from $1,069. The framed opening grows with the size — 38-1/2" on the 32, 42-1/2" here and 48-1/2" on the 42 — while framing height and depth stay at 34-1/4" and 19-3/4". The 36 and 42 take 24" and 30" log sets and the 32 takes 18" sets; the optional mesh cabinet doors fit only the 36 and 42.
Features
- 36" x 27" clean-face opening in a heat-circulating, radiant-face firebox — the angled box and air channels push more heat into the room
- Zero clearance to combustibles at the back, sides, top and floor — no chimney and no vent run
- Hosts any listed vent-free gas log heater up to 40,000 BTU/hr, sold separately — CSA design certified to fit most 18", 24" and 30" sets
- Reversible fiber panels ship standard in Multitonal Brown or Multitonal Gray — traditional brick on one face, herringbone on the other; reflective black glass is the optional third interior
- Built-in junction box — blower-ready and light-kit-ready with in-firebox or remote wall-box controls
- Hood, mesh firescreens that tuck into hide-away pockets and a two-piece hearth ship in the carton; adjustable floor supports carry heavy concrete log sets
Answers to common questions
What’s included, what’s required, and what’s optional?
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Included in the box: 36" x 27" clean-face firebox opening; Reversible fiber refractory panels — Multitonal Brown or Multitonal Gray (traditional or herringbone face); Hood (must be installed); Two mesh firescreen panels with hide-away screen pockets; Two-piece hearth for access without removing the log set; Built-in junction box; UL listing to CSA/ANSI Z21.91:20; HHT limited warranty — 20 yr parts / 3 yr labor on the firebox.
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Required to complete the installation, purchased separately: Vent Free Log Set (burner + logs/media) - make sure the Attribute 36" Firebox meets the minimum firebox dimensions. For a 36" box, The Torch Guys recommend 18" - 24" log sets; Gas Line - run by a qualified installer or licensed plumber through the side or bottom knockouts, with a regulator upstream if line pressure exceeds 1/2 PSIG.
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Optional: The 36" Contemporary Front, the trim kit for cabinet or drywall finishes, the ASD-36 mesh cabinet doors, the GFK-160VF blower, the MONAL-VF accent light kit, and the AKD outside air kit with 4" flex duct — the firebox operates fully without any of them; electrical power (unswitched 110-120 VAC to the junction box) is only needed when the log set or an accessory calls for it.
Does it need a chimney or a vent?
No — nothing about this firebox vents outside. The heater it hosts uses air from the room, so the installation must provide adequate combustion and ventilation air and stay out of drafts from exhaust fans, ceiling fans, return-air registers, windows and doors; an extremely tight home needs additional mechanical ventilation. Where a room runs tight, the optional AKD outside air kit ducts combustion air in through the side of the firebox.
Which log sets fit?
The firebox floor measures 32-7/8" across the front, 15" deep and 24-3/8" across the back, with 25-1/2" of height at the front and 22-5/8" at the back — those are Monessen's minimum-hearth figures for sizing a set, and the series is CSA design certified to fit most 18", 24" and 30" vent-free sets. The 36" takes 24" and 30" vent-free log sets, and any listed vent-free heater up to 40,000 BTU/hr may be used as long as the firebox meets that heater's own minimum size. Above 2,000 ft the heater's input is reduced 4% per 1,000 ft.
Where can it go — and where can't it?
Any ordinary living space that can spare combustion air — framed into a flat wall or a corner, directly on a combustible floor, with a perpendicular wall at least 9" from the opening and the ceiling at least 42" above it. Keep flammable objects 36" from the front, and over carpet, tile or vinyl set it on a metal or wood panel covering its full footprint with no carpet or vinyl within 14" of the opening; vinyl that runs to the wall calls for 14" of floor protection in front or a 12" raised opening. The unvented heater inside it cannot go in a bathroom, and only a heater rated 10,000 BTU/hr or less may go in a bedroom.
How high must a mantel or shelf be, and can a TV go above it?
The mantel answer depends on how far the mantel projects: combustible and non-combustible mantel and mantel-leg clearances are charted in Figures 7.1 through 7.4 on pages 18 and 19 of the installation manual, and reducing them means building the surround in non-combustible material to 12 inches above the framing height. Send us your mantel depth and we will read the chart with you. For a television, Monessen prints good-faith guidelines only — 17" from the top of the opening to a combustible mantel, 12" to a non-combustible one, shown in Figure 7.5 on page 20 — with the TV maker's own maximum operating temperature the deciding limit, so verify the actual TV temperature at installation.
Does it use electricity?
Only if something in it needs power. A junction box is built into the firebox and is wired to unswitched 110-120 VAC (the rating label reads less than 3 A at 115 V); not every log set needs 110 VAC, so a millivolt set can run with no power at all. Wire it in before the wall is closed if you might add the GFK-160VF blower or the MONAL-VF accent light kit — their controls mount in the firebox or in a remote wall box, and a circuit near a sink or in a bathroom must be GFCI-protected.
What are the interior panel choices, and what does "reversible" mean?
Every Attribute 36 ships with fiber refractory panels that are finished on both sides — a traditional brick face and a herringbone face — in Multitonal Brown on the ACUF36-BD or Multitonal Gray on the ACUF36-GD; the side and back panels lift out of their retainers and flip to show the second face. The third choice, Reflective Black Glass, adds the A36BGL black glass interior at extra cost. The hood, screens, clearances and framing are the same whichever you pick.
How does the warranty work if something goes wrong?
Hearth & Home Technologies warrants the firebox for 20 years on parts and 3 years on labor, the fiber refractory panels for 10 years parts and 1 year labor, and the junction box and other electrical parts for 2 years — coverage that transfers to a later owner of the home but applies only when the firebox was bought from an authorized dealer. The Torch Guys handles the claim for you: keep your invoice and the model and serial number, and we deal with the manufacturer on your behalf rather than handing you a phone number.
