CMC · California Mechanical Code

Conversion burners and burner assemblies — conversion and installation rules

If you’re installing or converting a burner in California, use a listed conversion burner (CSA Z21.8) and a listed burner assembly (UL 296 for oil; UL 295 for commercial gas), follow the manufacturer’s installation instructions exactly, and set the burner input per the appliance design (hot-water boilers require adjustment to within ±5% of design load). file

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Conversion burners must be installed to the specified listed standard: conversion burners are required to be installed in accordance with CSA Z21.8 per § 909.1. Burner assemblies must meet the applicable listing and be installed per the manufacturer’s instructions: oil burner assemblies must comply with UL 296 (§ 910.1) and commercial gas burner assemblies must comply with UL 295 (§ 910.2) — and be installed per the manufacturer’s instructions.

The single most important rule: every conversion burner or burner assembly must be a listed product and installed exactly per its listing and the manufacturer’s instructions (conversion burners per § 909.1; burner assemblies per § 910.1 and § 910.2).

Requirements in detail

Scope and basic mandate

  • Conversion burner: installation shall conform to CSA Z21.8 as required by § 909.1.
  • Burner assemblies: must be listed to the applicable UL standard and installed per manufacturer instructions:
    • Oil burners — comply with UL 296 and installed per manufacturer instructions (§ 910.1).
    • Gas burners (commercial) — comply with UL 295 and installed per manufacturer instructions (§ 910.2).

Adjustment, testing and startup (installation performance)

  • Installers must test safety and operating controls and venting, set the correct input and the fuel-to-air ratio, and adjust burners to the appliance design input. See the installer responsibilities in C105.1.
  • For conversion burners installed in hot water (liquid) boilers or warm air furnaces, the fuel rate (Btu/h) must be adjusted to within plus or minus 5 percent (±5%) of the design load, not exceeding the appliance’s design rate (C105.1).
  • For steam boilers, fuel input must be set in accordance with steam load requirements; oversized-boiler inputs must be established and added to total input demand (C105.1).

Installation practice (manufacturer’s instructions + listing)

  • Follow the burner or burner-assembly manufacturer’s installation instructions exactly — the CMC directs listed compliance and installation in accordance with manufacturer instructions for the assemblies in § 910.1 and § 910.2.

Quick decision table (decision-relevant dimensions/values)

Decision question Value / Requirement Code Reference
Standard required for conversion burners CSA Z21.8 § 909.1
Oil burner assembly listing UL 296 § 910.1
Commercial gas burner assembly listing UL 295 § 910.2
Hot-water boiler conversion-burner adjustment tolerance ±5% of design load C105.1
Draft hood requirement for conversion burners (where applicable) Draft hood must be listed or approved; if not supplied, install a listed/approved hood of same size as flue collar § 802.12.1 / Draft-hood rules referenced in CMC (see venting sections)

Exceptions & special cases

  • Draft-hood exception: some appliances are excepted from the draft hood requirement — importantly, single-firebox boilers equipped with conversion burners with inputs greater than 400,000 Btu/h (117 kW) are among the exceptions to the draft-hood requirement noted in the venting/draft-hood provisions. See the venting/draft-hood exception language (applies in the venting chapter referenced by the CMC).
  • If a draft hood is required for the conversion burner, it must be listed or approved and, absent other instructions, be the same size as the appliance flue collar; where supplied with the appliance it must be installed unaltered and per manufacturer’s instructions.
  • Manufacturer instructions control installation details not otherwise prescribed by the CMC; a listed burner/burner assembly installed contrary to its listing or instructions is not compliant with the CMC requirement in § 910.1 / § 910.2.

If you need a definitive ruling about whether a draft hood is required or whether a specific conversion is allowed without a hood (for example for that 400,000 Btu/h threshold), the CMC’s venting sections and the appliance listing must be consulted — see the related provisions below.

Common mistakes

  • Installing an unlisted conversion burner or burner assembly (not complying with CSA Z21.8, UL 296, or UL 295) instead of a listed product.
  • Ignoring the manufacturer’s installation instructions and the product listing; the code insists installation be in accordance with those instructions (§ 910.1, § 910.2).
  • Failing to adjust the burner fuel flow to the appliance design rate — especially the ±5% requirement for conversion burners on hot water boilers and warm-air furnaces (C105.1).
  • Omitting required venting or draft-hood components, or installing a draft hood not listed or sized incorrectly relative to the appliance flue collar.

Worked example — concrete scenario

Scenario: You install a conversion burner on an existing hot-water boiler whose marked design input is 250,000 Btu/h.

Step 1 — listing and standard: Select a conversion burner listed to CSA Z21.8 as required by § 909.1.

Step 2 — assembly standard: If the burner assembly is an oil burner assembly, verify assembly listing to UL 296 (§ 910.1) and follow the manufacturer instructions for mounting and controls. If commercial gas burner, verify UL 295 listing (§ 910.2).

Step 3 — adjust the fuel rate: Per C105.1, set the fuel flow (Btu/h) to within ±5% of 250,000 Btu/h:

  • Lower limit = 250,000 × 0.95 = 237,500 Btu/h
  • Upper limit = 250,000 × 1.05 = 262,500 Btu/h

Step 4 — venting/draft hood: Confirm whether a draft hood is required by the appliance listing and venting rules; if required and not supplied, install a listed draft hood of the same size as the flue collar and install it unaltered as directed by the venting provisions. (Note the draft-hood exception for single-firebox boilers with conversion burners >400,000 Btu/h does not apply here because 250,000 Btu/h < 400,000 Btu/h.)

Result: With a CSA Z21.8-listed conversion burner, a UL-listed burner assembly where applicable, manufacturer’s instructions followed, and the fuel rate adjusted to 237,500–262,500 Btu/h, the installation meets the cited CMC requirements discussed above. file

Related provisions

  • § 909.1 — Conversion burners shall conform to CSA Z21.8.
  • § 910.1 — Oil burners shall comply with UL 296 and be installed per manufacturer instructions.
  • § 910.2 — Commercial gas burners shall comply with UL 295 and be installed per manufacturer instructions.
  • C105.1 — Installer responsibilities: test controls and venting; set correct input and fuel/air; ±5% adjustment requirement for conversion burners on hot water boilers/warm-air furnaces.
  • Venting / draft hood provisions (installation, sizing, exceptions): see the venting and draft-hood sections described in the CMC (for example § 802.12.1 and related venting provisions that address draft hoods, their sizing, and exceptions).
  • Draft-hood exception list (appliances exempt from draft hoods, including single-firebox boilers with conversion burners >400,000 Btu/h): see venting chapter discussion and exceptions.

Code references

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

  • CMC § 108.1 High relevance — show source text

    The tag stating the date of the test and the name of the tester shall be

    attached to the appliance at the main valve.

    (b) Oil and liquid fuel burners of 1 000 000 Btu/h (293 kW) input or more require a supervised startup in accordance with Section C 108.1(10)(a).

    (c) Installation of oxygen trim systems, modulating dampers, or other draft control or combustion devices require a supervised startup in accordance with Section C 108.1(10)(a).

    2025 CALIFORNIA MECHANICAL CODE 399

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    APPENDIX C

    (d) Direct-fired heaters shall require a supervised startup in accordance with Section C 108.1(10)(a).

    (11)The complete control diagram of the installation and operating instructions shall be supplied and posted by the installer of the appliance.

    C 109.0 Special Requirements Based on Btu/h Input.

    C 109.1 General.

    (1) Zero to 400 000 Btu/h (0 kW to 117 kW) per burner.

    (a) One approved manual shutoff valve lever handle.

    (b) One approved fuel oil filter, installed on the supply piping.

    (c) Approved automatic safety shutoff valve to provide 100 percent shutoff of all oil.

    (d) A flame safeguard control capable of providing 100 percent shutoff in the event of flame failure. Flame failure response timing shall not exceed the control manufacturer’s instructions.

    (e) Two controls, one operating and one high limit, activated by temperature or pressure, as appropriate.

    (f) Burners relying on mechanical means to provide air for combustion shall have actual proof-of-air interlock device.

    (g) Installations with dampered combustion air openings shall prove damper open position before trial for burner ignition.

    (h) Vent dampers and flue dampers shall be properly interlocked to prevent burner ignition unless safely

    open.

    (2) Four hundred thousand and one to 999 999 Btu/h (117.2 kW to 292.9 kW) per burner.

    (a) One approved manual shutoff valve lever handle.

    (b) One approved fuel-oil filter, installed on the supply piping.

    (c) Two safety shutoff valves in series, maximum five seconds closing time.

    (d) One electronic flame safeguard pilot control providing a separately supervised and proven pilot, 100 percent shutoff manual reset. Flame failure response time shall not exceed the control manufacturer’s

    instructions.

    Direct-spark ignition shall be allowed where approved by the Authority Having Jurisdiction and where used on number 2 or lighter oil.

    (e) Two controls, one operating and one high limit, activated by temperature or pressure, as appropriate.

    (f) Burners relying on mechanical means to provide air for combustion shall have actual proof-of-air interlock device.

    (g) Power burners shall include proven prepurge of not less than 60 seconds at high-fire damper settings. This prepurge shall occur before every burner cycle, regardless of reason.

    (h) Installations with dampered combustion air openings shall prove damper open position before trial for burner ignition.

    (i) Vent dampers and flue dampers shall be interlocked to prevent burner ignition unless safely open.

    (j) One high oil or liquid fuel-pressure interlock, reset from flame safeguard or manually.

    (k) Where hot water or steam, one low water cutoff.

    (l) An atomizing medium proving switch.

  • CMC § 907.0 High relevance — show source text

    TABLE OF CONTENTS

    907.0 Wall Furnaces. . . . . . . . . . . . . . . . 204

    907.1 Application . . . . . . . . . . . . . . . . . . 204

    907.2 Installation . . . . . . . . . . . . . . . . . . 204

    907.3 Location . . . . . . . . . . . . . . . . . . . . 205

    907.4 Combustion and Circulating Air . . 205

    907.5 Oil-Fired Wall Furnaces . . . . . . . . 205

    908.0 Clothes Dryers . . . . . . . . . . . . . . . 205

    908.1 Application . . . . . . . . . . . . . . . . . . 205

    908.2 Electric Clothes Dryers . . . . . . . . . 205

    908.3 Gas-Fired Clothes Dryers. . . . . . . 205

    909.0 Conversion Burners . . . . . . . . . . . 205

    909.1 General. . . . . . . . . . . . . . . . . . . . . 205

    910.0 Burner Assemblies . . . . . . . . . . . . 206

    910.1 Oil Burners . . . . . . . . . . . . . . . . . . 206

    910.2 Gas Burners . . . . . . . . . . . . . . . . . 206

    911.0 Decorative Appliances for Installation in Vented Fireplaces. . . 206

    911.1 Application . . . . . . . . . . . . . . . . . . 206

    911.2 Prohibited Installations . . . . . . . . . 206

    911.3 Installation . . . . . . . . . . . . . . . . . . 206

    911.4 Fireplace Screens. . . . . . . . . . . . . 206

    912.0 Gas Fireplaces, Vented . . . . . . . . 206

    912.1 Application . . . . . . . . . . . . . . . . . . 206

    912.2 Reserved . . . . . . . . . . . . . . . . . . . 206

    912.3 Installation . . . . . . . . . . . . . . . . . . 206

    912.4 Combustion and Circulating Air . . . 206

    913.0 Factory-Built Fireplaces and Fireplace Stoves. . . . . . . . . . . . . . 206

    913.1 Factory-Built Fireplaces . . . . . . . . 206

    913.2 Fireplace Stoves. . . . . . . . . . . . . . 206

    913.3 Fireplace Accessories . . . . . . . . . 206

    914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters. . . 206

    914.1 Application . . . . . . . . . . . . . . . . . . 206

    914.2 Prohibited Installations . . . . . . . . . 206

    914.3 Installation . . . . . . . . . . . . . . . . . . 206

    914.4 Clearance from Combustible

    Materials . . . . . . . . . . . . . . . . . . . . 207

  • CMC § 103.0 High relevance — show source text

    Valve, Oil, Gas, or Fuel Control. An automatically or manually operated device consisting essentially of a fuel valve for controlling the fuel supply to a burner.

    C 103.0 Standards and Accepted Practices.

    C 103.1 General. The installation, testing, and repair of oil or liquid fuel-burning equipment systems shall be in accordance with this section, the standards listed in Chapter 18, and other information outlined in this code such as, but not limited to, combustion air, flue and breeching requirements, room clearances and dimensions, and control requirements.

    C 104.0 Approval of Equipment.

    C 104.1 General. Oil or liquid fuel-burning equipment shall be approved.

    C 105.0 Placing Equipment in Operation.

    C 105.1 General. After completion of installations, the installer shall test safety and operating controls and venting before placing the burner in service. The correct input of liquid fuel shall be determined, and the fuel-to-air ratio shall be set. Each oil or liquid fuel burner shall be adjusted to its input according to the manufacturer’s instructions. Overrating the burners or the appliance is prohibited. The input range shall be appropriate to the appliance:

    (1) For conversion burners installed in hot water (liquid) boilers or warm air furnaces, the rate of flow of the oil or liquid fuel in British thermal units per hour (Btu/h) (kW) shall be adjusted to within plus or minus 5 percent of the design load, not to exceed the design rate of the appli ance.

    (2) For conversion burners installed in steam boilers, the oil or liquid fuel hourly input demand shall be adjusted to be in accordance with the steam load requirements. The oil or liquid fuel input demand necessitated by an oversized boiler shall be established and added to total input demand.

    C 106.0 Pilot Operation.

    C 106.1 General. Igniter or pilot flames shall be effective to ignite the oil or liquid fuel at the main burner or burners and shall be adequately protected from drafts. Pilot flames shall not become extinguished during the pilot cycle where the main burner or burners are turned on or off in a normal manner either manually or by automatic controls.

    C 107.0 Burner Operation.

    C 107.1 General. In making tests to determine compliance with the requirements of this section, the following care shall be exercised to prevent the accumulation of unburned liquid fuel in the appliance that will result in an explosion or fire:

    (1) The flames from the burner shall ignite freely the liquid fuel where operating at the lowest firing position.

    (2) Burner flames shall not flash back where the liquid fuel is turned on or off by an automatic control mechanism.

    (3) Main burner flames shall ignite freely from the pilot where the pilot flame is reduced to a minimum point that will actuate the pilot safety device.

    (4) Where ignition is made in a normal manner, the flame will not flash outside the appliance.

    (5) Burners shall not expel liquid fuel through air openings where operating at prevailing pressure.

    (6) Burners shall have a liquid-fuel air mixture to ensure smooth ignition of the main burner.

    C 108.0 Method of Test.

    C 108.1 General Test Methods.

    (1) The flue gas, venting, safety and operating controls of the appliance shall be checked by the installer to ensure their proper and safe operation.

  • CMC § 905.8 High relevance — show source text

    905.8 Installation in Commercial

    Garages and Aircraft Hangars . . . 203

    905.9 Electric Duct Heaters . . . . . . . . . . 203

    906.0 Floor Furnaces . . . . . . . . . . . . . . . 203

    906.1 Application . . . . . . . . . . . . . . . . . . 203

    906.2 Installation . . . . . . . . . . . . . . . . . . 204

    906.3 Temperature Limit Controls . . . . . 204

    906.4 Combustion and Circulating Air. . . 204

    906.5 Placement. . . . . . . . . . . . . . . . . . . 204

    906.6 Bracing . . . . . . . . . . . . . . . . . . . . . 204

    906.7 Support . . . . . . . . . . . . . . . . . . . . . 204

    906.8 Clearance . . . . . . . . . . . . . . . . . . . 204

    906.9 Access . . . . . . . . . . . . . . . . . . . . . 204

    906.10 Seepage Pan . . . . . . . . . . . . . . . . 204

    906.11 Wind Protection . . . . . . . . . . . . . . 204

    906.12 Upper Floor Installations. . . . . . . . 204

    906.13 First Floor Installation . . . . . . . . . . 204

    906.14 Oil-Fired Floor Furnaces. . . . . . . . 204

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    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    TABLE OF CONTENTS

    907.0 Wall Furnaces. . . . . . . . . . . . . . . . 204

    907.1 Application . . . . . . . . . . . . . . . . . . 204

    907.2 Installation . . . . . . . . . . . . . . . . . . 204

    907.3 Location . . . . . . . . . . . . . . . . . . . . 205

    907.4 Combustion and Circulating Air . . 205

    907.5 Oil-Fired Wall Furnaces . . . . . . . . 205

    908.0 Clothes Dryers . . . . . . . . . . . . . . . 205

    908.1 Application . . . . . . . . . . . . . . . . . . 205

    908.2 Electric Clothes Dryers . . . . . . . . . 205

    908.3 Gas-Fired Clothes Dryers. . . . . . . 205

    909.0 Conversion Burners . . . . . . . . . . . 205

    909.1 General. . . . . . . . . . . . . . . . . . . . . 205

    910.0 Burner Assemblies . . . . . . . . . . . . 206

    910.1 Oil Burners . . . . . . . . . . . . . . . . . . 206

    910.2 Gas Burners . . . . . . . . . . . . . . . . . 206

    911.0 Decorative Appliances for Installation in Vented Fireplaces. . . 206

  • California Mechanical Code High relevance — show source text


    10|42
    32
    29
    24|76
    61
    56
    49|126
    102
    95
    86|185
    154
    141
    131|252
    210
    194
    180|340
    284
    264
    250|542
    451
    430
    406|815
    680
    648
    625| |10|0
    2
    5
    10
    15|45
    35
    32
    27
    NA|84
    67
    61
    54
    46|138
    111
    104
    94
    84|202
    168
    153
    143
    130|279
    233
    215
    200
    186|372
    311
    289
    274
    258|606
    505
    480
    455
    432|912
    760
    724
    700
    666| |15|0
    2
    5
    10
    15
    20|49
    39
    35
    30
    NA
    NA|91
    72
    67
    58
    50
    NA|151
    122
    110
    103
    93
    82|223
    186
    170
    158
    144
    132|312
    260
    240
    223
    207
    195|420
    350
    325
    308
    291
    273|684
    570
    540
    514
    488
    466|1040
    865
    825
    795
    760
    726| |20|0
    2
    5
    10
    15
    20|53
    42
    38
    32
    NA
    NA|101
    80
    74
    65
    55
    NA|163
    136
    123
    115
    104
    91|252
    210
    192
    178
    163
    149|342
    286
    264
    246
    228
    214|470
    392
    364
    345
    326
    306|770
    641
    610
    571
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    990
    945
    910
    870
    832| |30|0
    2
    5
    10
    15
    20
    30|56
    44
    NA
    NA
    NA
    NA
    NA|108
    84
    78
    68
    NA
    NA
    NA|183
    148
    137
    125
    113
    99
    NA|276
    230
    210
    196
    177
    163
    NA|384
    320
    296
    274
    258
    240
    192|529
    441
    410
    388
    366
    344
    295|878
    730
    694
    656
    625
    596
    540|1370
    1140
    1080
    1050
    1000
    960
    890| |50|0
    2
    5

  • CMC § 10.4.2 Medium relevance — show source text

    (3) Unlisted clothes dryers shall be installed with clearances to combustible material of not less than 18

    inches (457 mm). Combustible floors under unlisted clothes dryers shall be protected in an approved manner. {NFPA 54:10.4.2}

    908.3.2 Exhausting to the Outdoors. Type 1 and Type 2 clothes dryers shall be exhausted to the outside air in accordance with Section 504.4. {NFPA 54:10.4.3}

    908.3.3 Multiple-Family or Public Use. All clothes dryers installed for multiple-family or public use shall be installed as specified for a Type 2 clothes dryer under Section 504.4.3.1. [NFPA 54:10.4.7]

    909.0 Conversion Burners.

    909.1 General. Installation of conversion burners shall con form to CSA Z21.8. [NFPA 54:10.5]

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    shall be permitted to be an integral part of the vented wall furnace, as illustrated in Figure 907.2.1. The stud space in which the vented wall furnace is installed shall be ventilated at the first ceiling level by installation of the ceiling plate spacers furnished with the gas vent. Firestop spacers shall be installed at each subsequent ceiling or floor level penetrated by the vent. [NFPA 54:10.25.2.2]

    907.2.2 Direct Vent Wall Furnaces. Direct vent wall

    furnaces shall be installed with the combustion air intake

    terminal outdoors. [NFPA 54:10.25.2.3]

    907.2.3 Panels, Grilles, and Access Doors. Panels, grilles, and access doors that are required to be removed for normal servicing operations shall not be attached to the building. For additional information on the venting of wall furnaces, see Section 802.0. [NFPA 54:10.25.2.4]

    For SI units: 1 inch = 25.4 mm

    FIGURE 907.2.1

    INSTALLATION OF TYPE B-W GAS VENTS FOR

    VENTED WALL FURNACES

    [NFPA 54: FIGURE 10.25.2.2]

    907.3 Location. Wall furnaces shall be located so as not to cause a hazard to walls, floors, curtains, furniture, or doors. Wall furnaces installed between bathrooms and adjoining rooms shall not circulate air from bathrooms to other parts of the building. [NFPA 54:10.25.3]

    2025 CALIFORNIA MECHANICAL CODE 205

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    INSTALLATION OF SPECIFIC APPLIANCES

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    910.0 Burner Assemblies.

    910.1 Oil Burners. Oil burners shall comply with UL 296 and installed in accordance with the manufacturer’s installa tion instructions.

    910.2 Gas Burners. Commercial gas burners shall comply with UL 295 and installed in accordance with the manufac turer’s installation instructions.

    911.0 Decorative Appliances for Installation in Vented Fireplaces.

  • CMC § 2.0 Medium relevance — show source text

    0 psi**|2.0 psi| |||||||PRESSURE DROP:|PRESSURE DROP:|1.0 psi|1.0 psi| |||||||SPECIFIC GRAVITY:|SPECIFIC GRAVITY:|1.50|1.50| |INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR|INTENDED USE: PIPE SIZING BETWEEN 2 PSIG SERVICE AND LINE PRESSURE REGULATOR| ||PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)| |NOMINAL:|1⁄2|3⁄4|1|11⁄4|11⁄2|2|21⁄2|3|4| |ACTUAL ID:|0.622|0.824|1.049|1.380|1.610|2.067|2.469|3.068|4.026| |LENGTH
    (feet)|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR| |10
    20
    30
    40
    50|2680
    1840
    1480
    1260
    1120|5590
    3850
    3090
    2640
    2340|10 500
    7240
    5820
    4980
    4410|21 600
    14 900
    11 900
    10 200
    9060|32 400
    22 300
    17 900
    15 300
    13 600|62 400
    42 900
    34 500
    29 500
    26 100|99 500
    68 400
    54 900
    47 000
    41

  • CMC § 0.622 Medium relevance — show source text

    (LOW PRESSURE) REGULATOR**| ||PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)|PIPE SIZE (inch)| |NOMINAL
    INSIDE:|1⁄2|3⁄4|1|11⁄4|11⁄2|2|21⁄2|3|4| |ACTUAL:|0.622|0.824|1.049|1.380|1.610|2.067|2.469|3.068|4.026| |LENGTH
    (feet)|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR|CAPACITY IN THOUSANDS OF BTU PER HOUR| |10
    20
    30
    40
    50|3320
    2280
    1830
    1570
    1390|6950
    4780
    3840
    3280
    2910|13 100
    9000
    7220
    6180
    5480|26 900
    18 500
    14 800
    12 700
    11 300|40 300
    27 700
    22 200
    19 000
    16 900|77 600
    53 300
    42 800
    36 600
    32 500|124 000
    85 000
    68 200
    58 400
    51 700|219 000
    150 000
    121 000
    103 000
    91 500|446 000
    306 000
    246 000
    211 000
    187 000| |60
    70
    80
    90
    100|1260
    1160
    1080
    1010
    956|2640
    2430
    2260
    2120
    2000|4970
    4570
    4250
    3990
    3770|10 200
    9380
    8730
    8190
    7730|15 300
    14 100
    13 100
    12 300
    11 600|29 400
    27 100
    25 200
    23 600
    22 300|46 900
    43 100
    40 100
    37 700
    35 600|82 900
    76 300
    70 900
    66 600
    62 900|169 000
    156 000
    145 000
    136 000
    128

  • CMC § 12.13.1 Medium relevance — show source text

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    164 2025 CALIFORNIA MECHANICAL CODE

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    CHIMNEYS AND VENTS

    ances requiring chimney draft for operation; single-firebox boilers equipped with conversion burners with inputs greater than 400 000 Btu/h (117 kW); appliances equipped with blast, power, or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting. [NFPA 54:12.13.1]

    802.12.1 Installation. A draft hood supplied with or forming a part of a listed vented appliance shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

    If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type. [NFPA 54:12.13.2.1]

    802.12.2 Draft Control Devices. Where a draft con trol device is part of the appliance or is supplied by the appliance manufacturer, it shall be installed in accordance with the manufacturer’s instructions. In the

    absence of manufacturer’s instructions, the device shall be attached to the flue collar of the appliance or as near to the appliance as practical. [NFPA 54:12.13.3]

    802.12.3 Additional Devices. Appliances requiring controlled chimney draft shall be permitted to be equipped with listed double-acting barometric draft regulators installed and adjusted in accordance with the manufacturer’s instructions. [NFPA 54:12.13.4]

    802.12.4 Location. Draft hoods and barometric draft

    regulators shall be installed in the same room or enclosure as the appliance in such a manner as to prevent any difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:12.13.5]

    802.12.5 Positioning. Draft hoods and draft regulators shall be installed in the position for which they were designed with reference to the horizontal and vertical planes and shall be located so that the relief opening is not obstructed by any part of the appliance or adjacent construction. The appliance and its draft hood shall be located so that the relief opening is accessible for checking vent operation. [NFPA 54:12.13.6]

    802.12.6 Clearance. A draft hood shall be located so

    that its relief opening is not less than 6 inches (152 mm) from any surface except that of the appliance it serves and the venting system to which the draft hood is connected. Where a greater or lesser clearance is indicated on the appliance label, the clearance shall not be less than that specified on the label. Such clearances shall not be reduced. [NFPA 54:12.13.7]

    802.13 Manually Operated Dampers. A manually operated damper shall not be placed in any appliance vent connector. Fixed baffles and balancing baffles shall not be classified as manually operated dampers. Balancing baffles shall be mechanically locked in the desired position before

  • CMC § 510.1 Medium relevance — show source text

    (1) Draft regulators and safety controls specifically listed for installation in venting systems and installed in accordance with the manufacturer’s installation instructions.

    (2) Approved draft regulators and safety controls designed and installed in accordance with engineering methods.

    (3) Listed heat reclaimers and automatically operated vent dampers installed in accordance with the manufacturers’ installation instructions.

    (4) Vent dampers serving listed appliances installed in accordance with Section 510.1 or Section 510.2 or engineering methods.

    (5) Approved economizers, heat reclaimers, and recuperators installed in venting systems of appliances not required to be equipped with draft hoods, provided the appliance manufacturer’s instructions cover the installation of such a device in the venting system and performance in accordance with Section 509.3 and Section 509.3.1 is obtained. [NFPA 54:12.16]

    510.0 Sizing of Category I Venting Systems. 510.1 Additional Requirements to Single Appliance Vent. Venting Table 510.1.2(1) through Table 510.1.2(6) shall not be used where obstructions are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions or in accordance with the following:

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    B gas vents that pass through walls or partitions constructed of combustible material shall be installed

    with not less than the listed clearance to combustible

    material.

    (2) Vent connectors shall be permitted to pass through ceilings, floors, or walls in accordance with Section 509.7.3.1 and Section 509.7.3.5.

    509.10.13.1 Medium-Heat Appliances. Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material. [NFPA 54:12.11.14.2] 509.11 Vent Connectors for Category II, Category III, and Category IV Appliances. The vent connectors for Category II, Category III, and Category IV appliances shall be in accordance with Section 509.4 through Section 509.4.3.

    [NFPA 54:12.12]

    509.12 Appliances Requiring Draft Hoods. Vented appliances shall be installed with draft hoods.

    Exception: Dual oven-type combination ranges; direct vent appliances; fan-assisted combustion system appliances; appliances requiring chimney draft for operation; single-firebox boilers equipped with conversion burners with inputs greater than 400 000 Btu/h (117 kW); appliances equipped with blast, power, or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting. [NFPA 54:12.13.1]

    509.12.1 Installation. A draft hood supplied with or forming a part of a listed vented appliance shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

    If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type. [NFPA 54:12.13.2.1]

  • CMC § 907.4 Medium relevance — show source text

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    907.4 Combustion and Circulating Air. Combustion and circulating air shall be provided in accordance with Section 701.0. [NFPA 54:10.25.4]

    907.5 Oil-Fired Wall Furnaces. Oil-fired wall furnaces

    shall comply with UL 730 and installed in accordance with the manufacturer’s installation instructions.

    908.0 Clothes Dryers.

    908.1 Application. Clothes dryers shall be listed in accordance with ANSI Z21.5.1/CSA 7.1 for Type I clothes dryers or ANSI Z21.5.2/CSA 7.2 for Type II clothes dryers. [NFPA 54:10.4.1]

    908.2 Electric Clothes Dryers. Commercial electric clothes dryers shall comply with UL 1240 and installed in accordance with the manufacturer’s installation instructions.

    Residential and coin-operated electric clothes dryers shall comply with UL 2158 and installed in accordance with the manufacturer’s installation instructions.

    908.3 Gas-Fired Clothes Dryers. Gas-fired clothes dryers shall comply with Section 908.3.1 through Section 908.3.3.

    908.3.1 Clearance. The installation of clothes dryers shall comply with the following requirements:

    (1) Listed Type 1 clothes dryers shall be installed with a clearance of not less than 6 inches (152 mm) from adjacent combustible material. Clothes dryers listed for installation at reduced clearances shall be

    installed in accordance with their listing and the manufacturer’s installation instructions. Type 1 clothes dryers installed in closets shall be listed for such installation.

    (2) Listed Type 2 clothes dryers shall be installed with clearances of not less than those shown on the mark ing plate and in the manufacturer’s instructions. Type 2 clothes dryers designed and marked, “For use only in noncombustible locations,” shall not be installed elsewhere.

    (3) Unlisted clothes dryers shall be installed with clearances to combustible material of not less than 18

    inches (457 mm). Combustible floors under unlisted clothes dryers shall be protected in an approved manner. {NFPA 54:10.4.2}

    908.3.2 Exhausting to the Outdoors. Type 1 and Type 2 clothes dryers shall be exhausted to the outside air in accordance with Section 504.4. {NFPA 54:10.4.3}

    908.3.3 Multiple-Family or Public Use. All clothes dryers installed for multiple-family or public use shall be installed as specified for a Type 2 clothes dryer under Section 504.4.3.1. [NFPA 54:10.4.7]

    909.0 Conversion Burners.

    909.1 General. Installation of conversion burners shall con form to CSA Z21.8. [NFPA 54:10.5]

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    shall be permitted to be an integral part of the vented wall furnace, as illustrated in Figure 907.2.1. The stud space in which the vented wall furnace is installed shall be ventilated at the first ceiling level by installation of the ceiling plate spacers furnished with the gas vent. Firestop spacers shall be installed at each subsequent ceiling or floor level penetrated by the vent. [NFPA 54:10.25.2.2]

  • CMC § 802.10.5 Medium relevance — show source text

    802.10.5 Joints. Joints between sections of connector piping and connections to flue collars or draft hood outlets shall be fastened in accordance with one of the following methods:

    (1) Mechanically fastened by means of not less than three sheet-metal screws equally spaced around the joint.

    (2) Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in

    accordance with the manufacturer’s instructions.

    (3) Other approved means. {NFPA 54:12.11.6}

    802.10.6 Connector Junctions. Where vent connectors are joined together, the connection shall be made with a manufactured tee or wye fitting. [NFPA 54:12.11.7]

    802.10.7 Slope. A vent connector shall be installed without any dips or sags and shall slope upward toward the vent or chimney at least [1] ⁄ 4 inch per foot (20.8 mm/m).

    Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and the draft system manufacturers’ instructions. [NFPA 54:12.11.8]

    802.10.8 Length of Vent Connector. The length of vent connectors shall comply with Section 802.10.8.1 or Section 802.10.8.2.

    802.10.8.1 Single Wall Connector. The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent, except for engineered systems. [NFPA 54:12.11.9.1]

    802.10.8.2 Type B Double Wall Connector. The maximum horizontal length of a Type B double-wall connector shall be 100 percent of the height of the chimney or vent, except for engineered systems. The maximum length of an individual connector for a chimney or vent system serving multiple

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    164 2025 CALIFORNIA MECHANICAL CODE

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    CHIMNEYS AND VENTS

    ances requiring chimney draft for operation; single-firebox boilers equipped with conversion burners with inputs greater than 400 000 Btu/h (117 kW); appliances equipped with blast, power, or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting. [NFPA 54:12.13.1]

    802.12.1 Installation. A draft hood supplied with or forming a part of a listed vented appliance shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

    If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type. [NFPA 54:12.13.2.1]

    802.12.2 Draft Control Devices. Where a draft con trol device is part of the appliance or is supplied by the appliance manufacturer, it shall be installed in accordance with the manufacturer’s instructions. In the

Frequently asked questions

Can I field-convert a burner without using a listed conversion burner?

No. The CMC requires conversion burners to be installed in accordance with CSA Z21.8 (conversion burners must be listed or installed per that standard) — see § 909.1. Use of unlisted field modifications that are not conforming to the standard is not compliant.

If my appliance did not come with a draft hood, do I have to add one when I install a conversion burner?

If the appliance requires a draft hood (per the venting/draft-hood provisions), and one was not supplied, you must install a listed or approved draft hood sized per the appliance flue collar and manufacturer’s instructions; consult the venting provisions for details. Note exceptions exist (e.g., certain conversion burners on large single-firebox boilers) — see the venting chapter.

How exact must I set the fuel input after installing a conversion burner?

For conversion burners on hot water boilers or warm-air furnaces, set the fuel input to within ±5% of the appliance design load, and do not exceed the appliance design rate (C105.1).

Which listing applies to oil burner assemblies?

Oil burner assemblies must comply with UL 296 and be installed per the manufacturer’s instructions (§ 910.1).

Do I need an inspection or supervised startup for large burners?

The code requires installers to test controls and venting and to adjust inputs before placing burners in service (C105.1). Additional supervised startup requirements (for example in Appendix C) may apply to large oil/liquid fuel burners; consult the specific startup/testing sections and the appliance manufacturer. file

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