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Rooms Containing Fuel-Burning Appliances - Code Compliance Brief

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The intent of this brief is to provide code-related information about rooms containing fuel-burning appliances to help ensure that the measure will be accepted as being in compliance with the code. Providing notes for codes officials on how to plan review and conduct field inspections can help builders or remodelers with proposed designs and provide jurisdictional officials with information for acceptance. Providing the same information to all interested parties (e.g., code officials, builders, designers, etc.) is expected to result in increased compliance and fewer innovations being questioned at the time of plan review and/or field inspection.

As houses are being built "tighter" to meet stricter air leakage requirements (e.g., climate zones 1-3 at 5 ACH/50 [air changes per hour at 50 Pa]) and climate zones 3-8 at 3 ACH/50 in the 2015 International Energy Conservation Code (IECC) and International Residential Code (IRC), concern has risen for installing natural-draft gas appliances1 (vented2 or direct-vented appliances3) in these tighter homes without dealing with issues related to back-drafting due to possible increased negative pressure near the combustion4 appliance and drawing carbon monoxide into the building. For example, this scenario could potentially occur in a somewhat tight home tested at 900 cfm (cubic feet per minute) (e.g., a 2000-square foot home with 9-foot ceiling heights = 18,000 cubic feet/volume) by turning on one exhaust fan (e.g., 300 cfm), which could depressurize the home to the point that no natural-draft gas appliance could safely draft under these conditions5.

In an attempt to deal with these combustion issues, an entirely new section in the 2015 IECC/IRC regarding fuel-burning appliances basically requires the appliance to be isolated from the building thermal envelope,6 located either outside or within a separate room if the fuel-burning appliance is supplied by open combustion air ducts. The room must be insulated and sealed off from the rest of the conditioned space. Furthermore, a NEW Appendix 'RA' has been added providing for a Code Official's option to require a Combustion Appliance Zone (CAZ) test to verify "manufacturer's operational parameters" for venting byproducts of combustion in a "tight" <5 ACH/50 (air changes per hour) home.

This brief provides an overview of the requirements and further details of approving the actual "room," based on equipment choices and location of installed equipment, approving the "open combustion air ducts" as to the installation, insulation and sealing of the ducts, and any other ducts or water lines in the "room."

 

1"Appliance" is defined in the 2015 IECC/IRC as any apparatus or device that uses a fuel or raw material to produce light, heat, power, refrigeration, or air conditioning.
2"Appliance, vented" is defined as an appliance designed and installed in such a manner that all of the products of combustion are conveyed directly from the appliance to the outside atmosphere through an approved chimney or vent system.
3"Direct-vent appliance" is defined as an appliance that is constructed and installed so that all air for combustion is derived directly from the outside atmosphere and all flue gases are discharged directly to the outside atmosphere.
4"Combustion" is defined as in the context of the code referring to rapid oxidation of fuel accompanied by the production of heat or heat and light.
5Article on "IECC/IRC Code Conflict Regarding House Depressurization", Journal of Light Construction, Doug Garrett, Building Performance and Comfort, Inc., September 2013, http://www.jlconline.com/projects/energy-efficient/iecc-irc-code-conflict-regardign-house-depressurization_o.
6"Building Thermal Envelope" is defined as the basement walls, exterior walls, floor, roof, and any other building elements that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned space.

Plan Review

Per the 2015 IECC/IRC, Section R103.3/R106.3, Examination of Documents. The code official/building official must examine, or cause to be examined, construction documents for code compliance.

This section lists the applicable code requirements followed by details helpful for plan review regarding the provisions to meet the requirement for "rooms containing fuel-burning appliances." The first bullet item below is the code requirement itself. The remaining bullets are items to meet the requirement.

  • 2015 IECC/IRC, Section R402.4.4/N1102.4.4, Rooms Containing Fuel-Burning Appliances.  In Climate Zones 3 through 8, where open combustion air ducts provide combustion air to open combustion fuel-burning appliances, the appliances and combustion air opening shall be located outside the building thermal envelope or enclosed in a roomthat is isolated from inside the thermal envelope.  Such "rooms" must be sealed and insulated in accordance with the envelope requirements of the Insulation and Fenestration Requirement by Component Table R402.1.2/N1102.1.2, where the walls, floors and ceilings meet not less than the basement wall R-value requirement.  The door into the room should be fully gasketed and any water lines and ducts in the room insulated according to Section R403 (IECC)/Section N1103 (IRC) regarding Systems.  The combustion air duct(s) should be insulated to a minimum of R-8 where it passes through conditioned space.

    Exceptions:

    1. Direct vent appliances with both intake and exhaust pipes installed continuous to the outside.
    2. Fireplaces and stoves complying with Section R402.4.2 (IECC)/N1102.4.2 (IRC) and Section R1006 (IRC).

    — Construction Documentation.  Review the construction documents to identify the equipment, system controls, design, and ventilation choices for combustion air or supply air to equipment.  If combustion air vented appliances will be installed, confirm the provisions of the code provided in this brief.

    • 2015 IECC/IRC, Section R103.2/N1101.5 Information on Construction Documents.  Construction documents should include:
      • Insulation materials and their R-values
      • Mechanical system design criteria
      • Mechanical and service water-heating system and equipment types, sizes, and efficiencies
      • Equipment and system controls
      • Duct sealing, duct and pipe insulation and location
      • Air sealing details.

    — Insulation.  Review the construction documents and confirm that the insulation R-values specified meet or exceed the minimum insulation requirements for the "room."

    2015 IECC/IRC, Insulation and Fenestration Requirements by Component Table R402.1.2/N1102.1.2

    Climate Zone 3 4 except
    Marine    		 5 and
    Marine 4    		 6 7, 8
    Ceiling R-Value 38 49 49 49 49
    Wood Frame Wall R-Value 20 or 13+5 20 or 13+5 20 or 13+5 20 or 13+5 20+5 or 13+10
    Floor R-Value 19 19 30 30 38
    Basement Wall R-Valuea 5/13 5/13 15/19 15/19 15/19
    a The basement wall R-values are the minimum insulation requirements for the "room." The first R-value is continuous insulation with no thermal breaks; the second R-value is cavity insulation between studs or framing members.

    Code Compliant Minimum Insulation Levels for the "Room"

    Note: The actual code provision does not explicitly address requirements for any windows, skylights, slab-on-grade, or the door leading into the "room." If the "room" has any windows or skylights or is located as part of the building thermal envelope where one or more of the walls are exterior walls on a slab-on-grade foundation, then those components should meet the minimum insulation and fenestration values per Table R402.1.2/N1102.1.2. Also, because the "room" is to be isolated from the rest of the home, it should have an exterior type door (i.e., insulated door), not an interior door (i.e., hollow core) and should not have any grills or openings in it.

    Climate Zone 3 4 except
    Marine    		 5 and
    Marine 4    		 6 7, 8
    Ceiling, Wood Frame Walls, Floor R-Valuea 5/13 5/13 15/19 15/19 15/19
    a The first R-value is continuous insulation with no thermal breaks; the second R-value is cavity insulation between studs or framing members. Either one will meet the minimum insulation requirements for the "room."

    — Air Sealing/Air Leakage Control.  The same air sealing provisions for the building thermal envelope apply to the "room."

    • 2015 IRC/IECC, Air Barrier and Insulation Installation Table R402.4.1.1/N1102.4.1.1
      • Continuous air barrier7 – Confirm that construction documents specify a continuous air barrier for the building components that define the "room" to include the ceiling, walls, and floor.
      • Door – Confirm that the door leading into the room specifies a gasketing material and threshold.

    — Combustion Air Requirements.  There are five distinct methods in the IECC/IRC residential provisions where open combustion air ducts, provide combustion air, ventilation, and dilution air to fuel-burning appliances. To assist with which method would need to be met and that applies to an open combustion appliance in regards to where the air is being obtained for combustion, ventilation, and dilution of flue gases for the appliance and would result in having to meet the new provision for the "room," each method is listed below and states whether the requirement (method) must be met (applies or does not apply). Only one of the methods applies to the 2015 IECC/IRC, Section R402.4.4/N1102.4.4, Rooms Containing Fuel-Burning Appliances. Chapter 24, Fuel Gas, in the 2015 IRC is extracted from the 2015 edition of the International Fuel Gas Code (IFGC). The numbers in parentheses after each section number are the section numbers of the corresponding text in the IFGC, and the language in red and underlined explains why a particular method does or does not apply.

    1. G2407.5 (304.5) Indoor Combustion Air. ((NO! IECC/IRC R402.4.4/N1102.4.4 DOES NOT APPLY, as all the combustion air is obtained by way of abundant "indoor volume" in the home.))
      1. G2407.5.1 (304.5.1) Standard Method. The minimum required volume shall be 50 cubic feet per 1000 Btu/h (4.8 m3/kW) of the appliance input rating.
      2. G2407.5.2 (304.5.2) Known Air-Infiltration-Rate Method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined per the equations cited in this section.
    2. G2407.6 (304.6) Outdoor Combustion Air. Outdoor combustion air provided through opening(s) to the outdoors. The minimum dimension of air openings should not be <3 inches. ((YES! IECC/IRC, R402.4.4/N1102.4.4 APPLIES, as all the combustion air is obtained by way of abundant "indoor volume" in the home.)) Review and confirm that the construction documents specify the combustion air opening(s) meet one of the methods below.
      1. G2407.6.1 (304.6.1) Two-Permanent-Openings Method. Within 12 inches of the ceiling and 12 inches of the floor. Openings to communicate directly or by ducts with the outdoors or spaces that freely communicate with the outdoors.
        1. Vertical ducts – Each opening should have a minimum free area of 1 square inch per 4000 Btu/h of total input rating of all appliances in the enclosure.
        2. Horizontal ducts – Each opening should have a minimum free area of ≥1 square inch per 2000 Btu/h of total input rating of all appliances in the enclosure.
      2. G2407.6.2 (304.6.2) One-Permanent-Opening Method. Within 12 inches of the ceiling (top of enclosure) and appliance have clearances of at least 1 inch from the sides and back and 6 inches from the front of the appliance directly communicating with the outdoors or through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors with a minimum free area of 1 square inch per 3000 Btu/h of total input rating of all appliances located in the enclosure and not less than the sum of the areas of all vent connectors in the space.
    3. G2407.7 (304.7) Combination Indoor and Outdoor Combustion Air. ((NO! IECC/IRC R402.4.4/N1102.4.4 DOES NOT APPLY, as the combustion air is obtained by way some amount of "indoor volume" in the home and a direct connection to the outdoors. Due to lack of clarity in the language of R402.4.4/N1102.4.4, and the requisite connections required: 1) to the outdoors, and more importantly 2) to the indoors, an "isolated, insulated, enclosed room" is not possible.))
    4. G2407.8 (304.8) Engineered Installations. ((NO! IECC/IRC R402.4.4/N1102.4.4 DOES NOT APPLY, as all the combustion air is justified by way of an engineering analysis, signed and sealed by a registered design professional.))
    5. G2407.9 (304.9) Mechanical Combustion Air Supply. ((NO! IECC/IRC R402.4.4/N1102.4.4 DOES NOT APPLY, as all the combustion air is obtained by way of a direct or indirect connection to the outdoors, which is interlocked to the operation of the appliance.))

    — Insulation. Ducts and water lines in the "room"  

    • Review the construction documents and confirm the specified R-value of insulation for the combustion air ducts and for any other ducts in the "room."
      • Combustion air ducts, Section R402.4.4/N1102.4.4 require a minimum insulation R-value of R-8.
      • Other ducts, Section R403.3.1/N1103.3.1, supply and return ducts in portions of the building other than the attic require a minimum insulation R-value of R-6 if ducts are >3 inches in diameter or R-4.2 if ducts are <3 inches in diameter.
    • Review the construction documents and confirm the specified R-value of insulation for any mechanical system piping in the "room."
      • Mechanical System Piping Insulation, Section R403.4./N1103.4, require mechanical system piping capable of carrying fluids >105°F or <55°F insulated to a minimum of R-3.
    • Review the construction documents and confirm the specified R-value of insulation for any service hot water system piping in the "room."
      • Service Hot Water Systems, Hot Water Piping Insulation, Section R403.5.3/N1103.5.3, require hot water pipes to be insulated to a minimum of R-3.

 

7"Continuous air barrier" is defined as a combination of materials and assemblies that restrict or prevent the passage of air through the building thermal envelope.

Field Inspection

Per the 2015 IECC, Section R104, Inspections, construction or work for which a permit is required is subject to inspection. Construction or work is to remain accessible and exposed for inspection purposes until approved. Required inspections include footing and foundation, framing and rough-in work, plumbing rough-in, mechanical rough-in, and final inspection.

Per the 2015 IRC, Section R109, Inspections, the wording is somewhat different in that for onsite construction, from time to time the building official, upon notification from the permit holder or his agent, can make or cause to be made any necessary inspections. Further details are provided for inspections regarding foundation, plumbing, mechanical, gas and electrical, floodplain, frame and masonry, and final inspection. Any additional inspections are at the discretion of the building official. This section provides details for inspecting to the specific provisions for “rooms containing fuel-burning appliances” where one or more specific type of inspection per the IECC or IRC may be necessary to confirm compliance. The framing and rough-in inspection would be most likely the inspection to confirm code compliance for the "room."

  • Cavity insulation completely fills the cavity with no compression or gaps, the manufacturer’s R-value mark is readily available, and meets the approved R-value per construction documents.
  • Continuous insulation is installed in accordance with manufacturer’s installation instructions, the manufacturer’s R-value mark is readily available, and meets the approved R-value per construction documents.
  • Batt insulation is cut neatly around any wiring and plumbing, or insulation readily conforms to available space and extends behind piping and wiring.
  • Joints, seams, holes, and penetrations are caulked, gasketed, weather-stripped, or otherwise sealed.
  • Continuous air barrier is properly installed. Confirm the "room's" thermal envelope insulation for framed ceiling, walls, and floor is installed in substantial contact and continuous alignment with the air barrier.
  • Corners and headers are insulated and the junction of the foundation and sill plate is sealed. The junction of the top plate and top of exterior walls are sealed.
  • Any recessed lighting is sealed with a gasket or caulk between the housing and the interior walls or ceiling covering. Confirm the luminaires are IC-rated and labeled.
  • Door leading into the "room" is an insulated door, is weather-stripped with a threshold, and remains closed. The door remaining closed, is not so much a code requirement, but the essence of the isolated "room" is to keep it isolated from the rest of the home.
  • Combustion air opening(s) size and placement meet the approved construction documents.
  • Combustion air duct(s), other ducts, and piping are insulated properly and meet the approved R-values per the construction documents.
Technical Validation(s)

This section provides additional information and helpful resources.

Guide on Combustion Appliance Zone (CAZ) Testing, https://basc.pnnl.gov/resource-guides/combustion-appliance-zone-caz-testing

Measure Guideline: Combustion Safety for Natural Draft Appliances Through Appliance Zone Isolation, Fitgerald, Bohac, May 2014, https://basc.pnnl.gov/resource-guides/combustion-appliance-zone-caz-testing

Measure Guideline: Combustion Safety for Natural Draft Appliances Using Indoor Air, L. Brand, Partnership for Advanced Residential Retrofit, April 2014, http://www.gastechnology.org/Solutions/Documents/BAPARR-Reports/Measure-guidelines-combustion-safety-for-natural-draft-appliances-using-indoor-air.pdf

Natural Fuel Gas Code, 2015 Edition, http://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=54&year=2015

FAQ'S:

What are "open combustion air ducts?" "Combustion air" is regulated in the IRC. "Ducts" are defined in the IECC and regulated in the IRC. "Open" presumably refers to a duct that simply empties into a room, as opposed to a closed combustion system with direct vent appliance.

What are "open combustion fuel-burning appliances?" Open combustion fuel-burning appliances indicate any device that burns fuel and pulls air from the room surrounding the device. This would include gas kitchen stoves and presumably gas driers, but if a room in which these devices are used does not have "open combustion air ducts," there is no regulation.

What is "outside the building thermal envelope?" "Building thermal envelope" is defined in the 2015 IECC. To be "outside" the thermal envelope essentially requires tracing the thermal envelope (which is also regulated elsewhere in the 2015 IECC) and ensuring that the room is "outside" of that envelope. This might be in an unheated garage, an unheated basement, an unheated crawlspace, or even an unheated attic.

What is "isolated from inside the thermal envelope?" This phrase applies to a "room with the furnace" that is located inside the house. The room must be insulated and sealed off from the rest of the "conditioned space." The definition of conditioned space plays into this requirement because the combustion air is dumped into the room, the room is essentially unconditioned and the room must be sealed off from the conditioned space.