Fireplaces/Stoves with Proper Ventilation

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Proper Ventilated Fireplaces =
Ventilated Fireplace

Technical Description: 

Fireplaces need adequate combustion air to function properly and safely. Homes that are especially air tight or that have ventilation appliances like exhaust fans or clothes dryers operating may not have enough air to safely operate the fireplace. Combustion air can come from inside the home or from outdoors. Like other combustion appliances, fireplaces come in three types: natural-draft, mechanically drafted, and direct-vent. The first two take all or some of their combustion air from the indoor space. The third, direct-vent, takes 100% of its combustion air directly from outdoors. A direct-vent fireplace has a dedicated combustion air inlet that ducts air from the outside directly to the fireplace box and tight-fitting glass doors across the face of the fireplace opening to prevent room air from being used as combustion air. Direct-vent fireplaces are typically gas fueled. Because a direct-vent fireplace draws its combustion air directly from outdoors, it is not influenced by other exhaust fans or house air tightness; thus it is safer to operate.

Related Terms

Ventilated Fireplace
Sales Message
Ventilated fireplaces help ensure dangerous by-products from burning fossil fuel cannot back-draft into homes. What this means to you is your family can breathe better every day knowing your home is equipped to help manage a critical respiratory contaminant. Wouldn’t you agree protecting health is too important to ignore in new homes?

Climate

No climate specific information applies.

Description

A fireplace needs adequate combustion air to function properly and safely. Combustion air can come from inside the home or from outdoors. Like other combustion appliances, fireplaces come in three types: natural-draft, mechanically drafted, and direct-vent sealed-combustion. The first two take all or some of their combustion air from the indoor space. The third, direct-vent sealed-combustion, takes 100% of its combustion air directly from outdoors.

A direct-vent fireplace has a dedicated combustion air inlet that ducts air from the outside directly to the fireplace box and tight-fitting glass doors across the face of the fireplace opening to prevent room air from being used as combustion air. Direct van fireplaces are typically gas fueled. Because a direct-vent sealed-combustion fireplace draws its combustion air directly from outdoors, it is not affected by house air tightness or exhaust fan size.

A direct-vent sealed-combustion fireplace takes its combustion air directly from outside through a dedicated air inlet ducted to the firebox and vents combustion products directly outside

Figure 1. A direct-vent sealed-combustion fireplace takes its combustion air directly from outside through a dedicated air inlet ducted to the firebox and vents combustion products directly outside. Tightly fitting glass doors (not shown) cover the firebox combustion chamber and prevent the fireplace from back-drafting. (Image courtesy of CalcsPlus)

The mechanically drafted fireplace uses an exhaust fan attached to the top of the chimney. The exhaust fan pulls combustion gases up and out of the chimney while the fireplace is in use.  Some, if not all, of the combustion air typically comes from the conditioned space. Mechanically drafted fireplaces are less affected by building air tightness or indoor exhaust fans but they do have the ability to backdraft other naturally drafted appliances.

Natural-draft fireplaces are the most affected by the combination of building air tightness and mechanical exhaust systems. When a natural-draft fireplace is in full operation or at maximum burn, the natural draft of the fireplace will be hard to overcome; it can move as much as 400 CFM of air up the chimney. Because of the density expansion factor (about 1.6), only about 250 CFM is actually being exhausted out of the building. Nevertheless, it is possible for a natural-draft fireplace, at full burn, to backdraft other natural-draft-vented combustion appliances in the home.

However, when the chimney is cooler, such as when a fire is just getting started in a cold fireplace or when a fire has burned down or is on a low flame, the natural-draft fireplace is more vulnerable to being backdrafted. During these conditions, a small kitchen or bath exhaust fan (50 CFM) could backdraft the combustion pollutants from the fireplace into the home. To avoid this, install a dedicated combustion air duct to bring outside air directly to the fireplace for combustion air and select a fireplace with tight-fitting glass doors.

How to Test for Proper Ventilation of Natural-Draft Fireplaces

  1. If installing a natural-draft fireplace, install a dedicated combustion air duct that brings outside air directly into the firebox. Install a fireplace that has tight-fitting glass doors across the face of the fireplace opening.
  2. The rater will verify that the total net rated exhaust flow of the two largest exhaust fans is <= 15 CFM per 100 ft 2 of occupiable space.
    • Calculate the total occupiable space of the house. Per ASHRAE 62.2-2010, occupiable space is any enclosed space inside the pressure boundary and intended for human activities, including, but not limited to, all habitable spaces, toilets, closets, halls, storage and utility areas, and laundry areas.
    • Calculate the net rated exhaust flow of the two largest exhaust fans. Per ASHRAE 62.2-2010 and published addenda, the term “net-exhaust flow” is defined as flow through an exhaust system minus the compensating outdoor air flow through any supply system that is interlocked to the exhaust system. Add together the rated exhaust flow of the two largest exhaust fans in the home. Subtract the air flow of any dedicated supply ventilation.
    • Verify the total net rated exhaust flow is less than or equal to 15 CFM per 100 ft 2 of occupiable space:
      15 CFM per 100 ft 2 >= ((Largest Fan Rated Flow) CFM + (Second Largest Fan Rated Flow) CFM - (Supply Outdoor Air Intake) CFM ) / (Occupiable Space) ft 2

Or, the rater will verify that the pressure differential is <= -5 Pa using BPI’s or RESNET’s worst-case depressurization test procedure. Raters shall use either the Building Performance Institute’s (BPI’s) Combustion Safety Test Procedure for Vented Appliances or RESNET’s Interim Guidelines for Combustion Appliance Testing & Writing Work Scope and be BPI-certified or RESNET-certified to follow the protocol. If using RESNET’s worst-case depressurization protocol to evaluate fireplaces, the blower door shall not be set to exhaust 300 CFM to simulate the fireplace in operation, but the remainder of the protocol shall be followed. Note that the fireplace damper should be closed during the test.

Ensuring Success

If a fireplace is installed, make sure it has adequate ventilation. If the fireplace is naturally drafted, the rater must verify that the total net rated exhaust flow of the two largest exhaust fans is <= 15 CFM per 100 ft2 of occupiable space, or the rater must verify that the pressure differential is <= -5 Pa using BPI’s or RESNET’s worst-case depressurization test procedure.

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Scope

If fireplaces are installed, ensure that ventilation air is provided directly to the fireplace and conduct combustion safety testing to ensure the fireplace will not be backdrafted by other exhaust fans in the home.

DOE Zero Energy Ready Home Notes

The DOE Zero Energy Ready Home Program requires that builders comply with the EPA Indoor airPLUS Program. The Indoor airPLUS checklist (Item 5.1) requires that builders meet certain requirements for fuel-burning and space-heating appliances that are located in conditioned space.

Completion of the ENERGY STAR checklists (which is a DOE Zero Energy Ready Home requirement) now satisfies the following Indoor airPLUS requirements:

Fireplaces that are not mechanically drafted or direct-vented to the outdoors must meet maximum allowed exhaust flow or pressure differential (HVAC-R 10.2).

Additional Indoor airPLUS requirements:

Do not install any unvented combustion space-heating appliances.

Ensure naturally drafted fuel-burning appliances located in conditioned spaces are installed in compliance with ASHRAE 62.2-2010 (Section 6.4) or conduct a worst case depressurization combustion air zone (CAZ) test according to an established protocol.

Ensure that all fireplaces and other fuel-burning and space-heating appliances located in conditioned spaces are vented to the outdoors and supplied with adequate combustion and ventilation air according to the manufacturers’ installation instructions.

Meet the following energy efficiency and emissions standards and restrictions for all fireplaces and other fuel-burning and space-heating appliances located in conditioned spaces:

  • Traditional masonry fireplaces designed for open fires are not permitted, with the exception of “masonry heaters” as defined by ASTM E1602 and Section 2112.1 of the 2012 International Building Code (i.e., fireplaces engineered to store and release substantial portions of heat generated from a rapid burn).
  • Factory-built wood-burning fireplaces shall meet the certification requirements of UL 127 and emission limits found in the EPA Standard for New Residential Wood Heaters.
  • Natural gas and propane fireplaces shall be mechanically drafted or direct vented, as defined by NFPA 54, Section 3.3.108, have a permanently affixed glass front or gasketed door and comply with ANSI Z21.88/CSA 2.33.
  • Wood stove and fireplace inserts as defined in Section 3.8 of UL 1482 shall meet the certification requirements of that standard, and they shall meet the emission requirements of the EPA Standard for New Residential Wood Heaters and WAC 173-433-100 (3).
  • Pellet stoves shall meet the requirements of ASTM E1509.
  • Decorative gas logs as defined in K.1.11 of NFPA 54 (National Fuel Gas Code) are not permitted.

Note: Unfinished basements and crawlspaces (except raised pier foundations with no walls) and attached garages that are air-sealed to the outside and intended for use as work or living space, are considered “conditioned spaces” for the purpose of this requirement.

ENERGY STAR Certified Homes Notes

ENERGY STAR Ver. 3, Rev. 07, in the HVAC System Quality Installation Rater Checklist requires the following in Section 10, Combustion Appliances.

10.2 For fireplaces that are not mechanically drafted or direct-vented to outdoors, total net rated exhaust flow of the two largest exhaust fans (excluding summer cooling fans) is <= 15 CFM per 100 sq. ft. of occupiable space when at full capacity or the Rater has verified that the pressure differential is <=5 Pa using BPI’s or RESNET’s worst-case depressurization test procedure. See the Compliance tab for additional details.

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Compliance

DOE Zero Energy Ready Home

The DOE Zero Energy Ready Home Program requires that builders comply with the EPA Indoor airPLUS Program. The Indoor airPLUS checklist (Item 5.1) requires that builders meet certain requirements for fuel-burning and space-heating appliances that are located in conditioned space.

Completion of the ENERGY STAR checklists (which is a DOE Zero Energy Ready Home requirement) now satisfies the following Indoor airPLUS requirements:

Fireplaces that are not mechanically drafted or direct-vented to the outdoors must meet maximum allowed exhaust flow or pressure differential (HVAC-R 10.2).

Additional Indoor airPLUS requirements:

Do not install any unvented combustion space-heating appliances.

Ensure naturally drafted fuel-burning appliances located in conditioned spaces are installed in compliance with ASHRAE 62.2-2010 (Section 6.4) or conduct a worst case depressurization combustion air zone (CAZ) test according to an established protocol.

Ensure that all fireplaces and other fuel-burning and space-heating appliances located in conditioned spaces are vented to the outdoors and supplied with adequate combustion and ventilation air according to the manufacturers’ installation instructions.

Meet the following energy efficiency and emissions standards and restrictions for all fireplaces and other fuel-burning and space-heating appliances located in conditioned spaces:

  • Traditional masonry fireplaces designed for open fires are not permitted, with the exception of “masonry heaters” as defined by ASTM E1602 and Section 2112.1 of the 2012 International Building Code (i.e., fireplaces engineered to store and release substantial portions of heat generated from a rapid burn).
  • Factory-built wood-burning fireplaces shall meet the certification requirements of UL 127 and emission limits found in the EPA Standard for New Residential Wood Heaters.
  • Natural gas and propane fireplaces shall be mechanically drafted or direct vented, as defined by NFPA 54, Section 3.3.108, have a permanently affixed glass front or gasketed door and comply with ANSI Z21.88/CSA 2.33.
  • Wood stove and fireplace inserts as defined in Section 3.8 of UL 1482 shall meet the certification requirements of that standard, and they shall meet the emission requirements of the EPA Standard for New Residential Wood Heaters and WAC 173-433-100 (3).
  • Pellet stoves shall meet the requirements of ASTM E1509.
  • Decorative gas logs as defined in K.1.11 of NFPA 54 (National Fuel Gas Code) are not permitted.

Note: Unfinished basements and crawlspaces (except raised pier foundations with no walls) and attached garages that are air-sealed to the outside and intended for use as work or living space, are considered “conditioned spaces” for the purpose of this requirement.

ENERGY STAR Certified Homes

ENERGY STAR Ver. 3, Rev. 07, in the HVAC System Quality Installation Rater Checklist requires the following in Section 10, Combustion Appliances.

10.2 For fireplaces that are not mechanically drafted or direct-vented to outdoors, total net rated exhaust flow of the two largest exhaust fans (excluding summer cooling fans) is <= 15 CFM per 100 sq. ft. of occupiable space when at full capacity or the Rater has verified that the pressure differential is <= -5 Pa using BPI’s or RESNET’s worst-case depressurization test procedure. (26,36,37,38)

ENERGY STAR Footnotes:

(26) Per ASHRAE 62.2-2010, an exhaust system is one or more fans that remove air from the building, causing outdoor air to enter by ventilation inlets or normal leakage paths through the building envelope (e.g., bath exhaust fans, range hoods, clothes dryers).

(35) The pressure boundary is the primary enclosure boundary separating indoor and outdoor air. For example, a volume that has more leakage to outside than to conditioned space would be outside the pressure boundary.

(36) Raters shall use either the Building Performance Institute’s (BPI’s) Combustion Safety Test Procedure for Vented Appliances or RESNET’s Interim Guidelines for Combustion Appliance Testing & Writing Work Scope and be BPI-certified or RESNET-certified to follow the protocol. If using RESNET’s worst-case depressurization protocol to evaluate fireplaces, per Item 10.2, the blower door shall not be set to exhaust 300 CFM to simulate the fireplace in operation, but the remainder of the protocol shall be followed.

(37) Per ASHRAE 62.2-2010 and published addenda, the term “net-exhaust flow” is defined as flow through an exhaust system minus the compensating outdoor airflow through any supply system that is interlocked to the exhaust system. “Net supply flow” is intended to represent the inverse. If net exhaust flow exceeds allowable limit, it shall be reduced or compensating outdoor airflow provided.

(38) Per ASHRAE 62.2-2010, occupiable space is any enclosed space inside the pressure boundary and intended for human activities, including, but not limited to, all habitable spaces, toilets, closets, halls, storage and utility areas, and laundry areas. 

BPI’s Combustion Safety Test Procedure for Vented Appliances is available HERE.

RESNET’s Interim Guidelines for Combustion Appliance Testing and Writing Work Scope are available HERE.

ANSI/ASHRAE Standard 62.2

Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings.  The standard applies to spaces intended for human occupancy in single-family homes and multifamily homes that are three stories or less, including manufactured and modular homes.  The standard provides minimum acceptable requirements for mechanical and natural ventilation in these spaces.

2009 IECC

Wood-burning fireplaces should have doors with gaskets and should have outdoor combustion air.

2009 IRC

Chapter 10 of the 2009 IRC describes fireplace and chimney requirements, including clearances, flues, and seismic reinforcement. Section R1006 specifies that fireplaces must be equipped with an exterior air supply that brings air from outside or from a vented attic or crawlspace directly to the firebox for combustion, unless the room is mechanically ventilated in a way that maintains neutral or positive air pressure in the room.

2012 IECC

Wood-burning fireplaces should have tight-fitting flue dampers and should have outdoor combustion air.

2012 IRC

Chapter 10 of the 2012 IRC describes fireplace and chimney requirements, including clearances, flues, and seismic reinforcement. Section R1006 specifies that fireplaces must be equipped with an exterior air supply that brings air from outside or from a vented attic or crawlspace directly to the firebox for combustion, unless the room is mechanically ventilated in a way that maintains neutral or positive air pressure in the room.

More Info.

Case Studies

  1. Author(s): NSTAR, PARR
    Organization(s): NSTAR, PARR
    Publication Date: May, 2014

    Case study describing a method for evaluating safe installation and operation of combustion appliances in homes undergoing energy efficiency upgrades where indoor air is used for combustion and venting.

References and Resources*

  1. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2014

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  2. Author(s): EPA
    Organization(s): EPA
    Publication Date: June, 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  3. Author(s): EPA
    Organization(s): EPA
    Publication Date: November, 2013

    Document outlining specifications that were developed by the U.S. Environmental Protection Agency (EPA) to recognize new homes equipped with a comprehensive set of indoor air quality (IAQ) features.

  4. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2009

    Code containing 2009 ICC language for mechanical draft systems.

  5. Author(s): National Fire Protection Association
    Organization(s): National Fire Protection Association
    Publication Date: August, 2013

    Standard providing guidelines for construction projects involving chimneys, fireplaces, venting systems, and solid fuel-burning appliances.

Last Updated: 06/12/2014

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