The Natural Blaze NB18 / NB24 from Monessen
No chimney and no household power. The Monessen Natural Blaze is a vent-free gas log burner listed as an unvented room heater and as a vented decorative log set, in two sizes: the 18" NB18 at 29,000 BTU/hr on natural gas (28,000 on propane) for a fireplace at least 26" wide at the front, and the 24" NB24 at 37,000 (36,000) for one at least 29" wide with 24" logs or 33" with 30" logs — both 14-1/2" deep and 17" high — with millivolt or IntelliFire Plus battery ignition. It ships as the burner with its grate, two bags of lava rock, rock wool, switch, flex line and floor anchors; the Beachcomber, Berkley Oak, Highland Oak or Stony Creek log set sized to the burner is sold separately. from $999.
Choose the Natural Blaze if you already have a masonry fireplace, a UL127 factory-built fireplace or a listed vent-free firebox and want a tall, lively yellow flame over a glowing ember bed without a chimney run, a gas conversion or an electrical circuit. Pick the 18" burner for a fireplace floor at least 26" wide at the front and the 24" for one at least 29" wide (33" if you want the 30" log sets); both need 14-1/2" of depth and 17" of height, and the log set is chosen to match. The millivolt version keeps working through a power outage; the IntelliFire Plus version adds battery ignition and the RC300 remote in the box. Dual listing means that if a mantel or wall clearance cannot be met, the same burner can run vented with the damper open.
It is not right for a bedroom or bathroom — every version of this burner is rated above the 10,000 BTU/hr that unvented appliances are allowed there. It is not a primary heat source, it takes its combustion air from the room and puts about an ounce of water vapor into it per 1,000 BTU each hour, so a very tightly sealed house without added ventilation, or a room smaller than the manual's 50 cubic feet per 1,000 BTU/hr (1,450 cubic feet for the smaller burner at full input, 1,850 for the larger), is the wrong place for it. It is also not a stand-alone appliance: without a masonry fireplace, a UL127 factory-built fireplace or a listed vent-free firebox that meets its minimum hearth dimensions there is nothing to install it in, and a glass-door frame or lip that rises more than 3" in front of the burner is not recommended by the manufacturer.
Specifications
The fireplace or firebox floor must be at least 14-1/2" deep and 17" high for either burner; the front width depends on the burner and log-set size — 26" for the 18" burner with 18" logs (20-1/4" at the back), 29" for the 24" burner with 24" logs (23-1/4" at the back) and 33" with 30" logs (25-1/4" at the back) — with the log set against or as close as possible to the rear wall, and the same row applies whether the burner is millivolt or IntelliFire Plus. A glass-door frame in front of the burner changes the numbers: no restriction needs 14-1/2" of depth, a 0"-3" lip needs 16-1/2", and anything taller is not recommended. Sidewalls stay 9" from the side of the opening and the ceiling 42" above it; the material above the opening must be non-combustible — 12" or more of it needs no hood, 8"-12" requires the optional CABL hood, less than 8" is not allowed. A combustible mantel sits 14" above the opening if it is 3" deep, 17" at 6", 20" at 9" and 23" at 12" (8", 11", 14" and 17" with the hood); if those cannot be met the burner runs vented with the damper open. Combustible flooring other than carpet or vinyl may come right to the opening, but no carpet or vinyl within 14" of the face, and vinyl running to the wall calls for 14" of floor protection or an opening raised 12". Gas pressure is 5.0"-10.0" w.c. inlet and 3.5" manifold on natural gas, 11.0"-13.0" and 10.0" on propane, through a 3/8" line to the right-rear inlet; the 18" burner weighs 30 lb and the 24" 35 lb, and either anchors to the floor with two screws.
Features
- Natural Blaze burner technology — taller, livelier yellow flames that light instantly over an ember bed of rock wool and lava rock
- Dual listed: an unvented room heater (CSA/ANSI Z21.11.2) or a vented decorative log set with the damper open (ANSI Z21.60)
- 29,000 BTU/hr on the 18" burner or 37,000 on the 24" (natural gas), with an ODS safety pilot that shuts the burner down if room oxygen drops
- No household power: a self-powered millivolt valve with piezo igniter, or IntelliFire Plus IPI on four AA batteries with the RC300 remote in the box
- Ships with the grate assembly, on/off switch, two bags of lava rock, rock wool, anchor screws, flex line and fittings — add the Beachcomber, Berkley Oak, Highland Oak or Stony Creek logs sized to the burner
- Anchors to the fireplace floor of a masonry fireplace, UL127 factory-built fireplace or listed vent-free firebox
Answers to common questions
What’s included, what’s required, and what’s optional?
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Included in the box: Natural Blaze gas log burner assembly with ODS safety pilot; Grate assembly that positions and supports the logs; On/off switch and wire harness; Two bags of lava rock and one bag of rock wool embers; Flex gas line and pipe fittings with 1/2" T-handle shutoff valve; Fastener pack with two anchor screws; UL listing to CSA/ANSI Z21.11.2:19 and ANSI Z21.60-2017; HHT limited warranty — 5 years on the burner.
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Required to complete the installation, purchased separately: Log Set - one set sized to the burner: 18" Beachcomber, Berkley Oak (refractory or fiber), Highland Oak or Stony Creek for the 18" burner; the 24" or 30" version of the same sets for the 24" burner; the burner must never be operated without a log set installed; Fireplace or Firebox - a solid-fuel masonry fireplace, a UL127 factory-built fireplace or a listed vent-free firebox whose floor meets the minimum hearth dimensions for the burner and log set chosen; Gas Line - a 3/8" supply run and purged by a qualified installer or licensed plumber, with a regulator upstream if line pressure exceeds 1/2 PSIG (an external regulator is required for propane).
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Optional: For millivolt models the RCB on/off remote, TSST thermostat remote, TS thermostat sensor, RRCM receiver cover and HILOKTN / HILOKTP variable-flame kits (not with Stony Creek logs); for IPI models the ACCK-IPIP 6 VDC transformer; for any install the CABL adjustable hood (needed only when the non-combustible facing above the opening is 8"-12"), C-CLAMP damper clamps for vented use and extra VR1000A volcanic rock — the burner operates fully without any of them.
Which size should I choose, the 18" or the 24"?
Match the burner to the fireplace floor and the log set you want. The 18" burner needs a fireplace at least 26" wide at the front (20-1/4" at the back), 14-1/2" deep and 17" high, and runs 29,000 BTU/hr on natural gas or 28,000 on propane. The 24" burner needs 29" of front width with 24" logs or 33" with 30" logs, the same 14-1/2" depth and 17" height, and runs 37,000 BTU/hr on natural gas or 36,000 on propane; it is the only one that takes the 30" log sets. Both share the ignition choices, the listings, the clearances and the accessory list. If your fireplace is wider than the minimum, either burner fits; the larger set simply fills more of the opening.
Where can it be installed — and where can't it?
Inside a solid-fuel masonry fireplace, a UL127 factory-built fireplace whose instructions do not exclude unvented logs, or a listed vent-free firebox — never free-standing, and never in a bedroom or bathroom, because every version of this burner is rated above the 10,000 BTU/hr that unvented codes allow there. The fireplace floor must meet the minimum hearth dimensions for the burner and log set (26" front width x 14-1/2" deep x 17" high for the smallest), the room must not be a confined space (50 cubic feet per 1,000 BTU/hr — 1,450 cubic feet at the smaller burner's full input, 1,850 at the larger) and it needs to be out of drafts from fans, range hoods and return-air vents, with flammable objects at least 36" from the front. Above 2,000 ft the input is derated 4% per 1,000 ft, and a manufactured home is fine where local codes allow it.
Does it need a chimney, and what does dual rated mean?
No chimney is needed for vent-free use: the burner is listed as an unvented room heater, an ODS safety pilot shuts it off if room oxygen drops, and a damper stop is required on the fireplace damper so it cannot close fully (one is provided with the appliance, though the carton list does not name it, so check the carton and ask us if it is missing). The same burner is also listed as a vented gas log set — run with the chimney and damper open when a mantel or wall clearance cannot be met, or when you prefer to vent the moisture outside. Vented, the damper must stay open to the free area in the manual's tables (16.6 sq in for the 18" burner or 22.1 sq in for the 24" at a 10 ft factory-built chimney; 25.7 or 33.8 sq in at a 6 ft masonry chimney), a thermostat is not allowed, and Massachusetts requires the damper permanently removed or welded open.
Does it need electricity or batteries?
No household power is needed for either ignition system, and line voltage must never be wired to the valve. The millivolt version is a self-powered standing pilot lit with the piezo igniter and shipped with a decorative on/off switch log; an optional wall switch, thermostat or remote wires to the valve. The IntelliFire Plus version runs its intermittent pilot on four AA batteries in an integrated pack and comes with the RC300 remote paired to it — the optional ACCK-IPIP transformer runs it from 120 V instead, and frequent flame adjustment from the remote shortens battery life.
How high must a mantel or shelf above the opening be?
That depends on how deep the mantel is, and the table is the same for both burner sizes: a combustible mantel 3" deep sits at least 14" above the fireplace opening, 6" deep at 17", 9" deep at 20" and 12" deep at 23" — or 8", 11", 14" and 17" with the optional CABL adjustable hood installed. The wall directly above the opening must be non-combustible (slate or marble at least 1/2" thick): 12" or more of it needs no hood, 8"-12" requires the hood, and less than 8" is not allowed. Sidewalls stay 9" from the side of the opening and the ceiling 42" above it. If a clearance cannot be met, the burner must be installed and run as a vented appliance with the chimney and damper open. Send us your mantel depth and we will check the table with you.
What controls and remotes work with it?
That depends on the ignition, and each version has its own list. The IntelliFire Plus version ships with the RC300 remote already paired to its control module, so nothing else is required. The millivolt version ships with the decorative on/off switch log, and Monessen sells the RCB battery on/off remote, the TSST touch-screen thermostat remote, the TS thermostat sensor, the HILOKTN (natural gas) and HILOKTP (propane) variable-flame remote kits and the RRCM insulated receiver cover for it; the receiver's piggy-back terminal lets a remote and a wall switch share the valve, and mounting the receiver in a wall keeps heat from shortening its battery life. The price book excludes the variable-flame kits from use with the Stony Creek logs; no other log set is excluded. A thermostat of any kind is allowed only in a vent-free installation.
How does the warranty work if something goes wrong?
Hearth & Home Technologies backs the Natural Blaze with its limited warranty: 5 years on the burner and logs, 2 years on valves, pilots, modules and remotes, 1 year on other parts, transferable to a later owner of the home and printed in full on pages 4-5 of the manual. The Torch Guys is an authorized Monessen dealer, so buying from us does not affect it — keep your invoice and the model and serial number from the tag on the burner, and we handle the claim with the manufacturer for you.
