Fireplaces/Stoves with Proper Ventilation
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.
- Meet applicable code requirements for the installed fireplace, woodstove, pellet stove, or masonry heater.
See the Compliance Tab for related codes and standards, and criteria to meet national programs such as ENERGY STAR, DOE’s Zero Energy Ready Home program, and EPA’s Indoor airPLUS.
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 vent 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.
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.
For wood-burning stoves and other appliances EPA implemented the Residential Wood Heater New Source Performance Standard (NSPS) and two voluntary programs - the Fireplace Program and the Hydronic Heater Program to help improve wood-burning devices and substantially reduce pollutant emissions to the outdoor air while maintaining energy efficiency.
EPA-Certified wood stoves meet the requirements of the NSPS, which has governed the manufacture and sale of wood stoves and certain wood-burning fireplace inserts based on emissions testing since 1988. EPA-Qualified appliances, such as wood fireplaces and wood hydronic heaters, meet emission levels set by EPA’s Voluntary Fireplace and Hydronic Heater Programs. An EPA-certified appliance must adhere to regulatory emission requirements established by EPA, while appliances that meet the voluntary emission standards set by EPA are considered "EPA-qualified."
EPA-Certified wood stoves typically use up to one-third less firewood than older, less-efficient stoves. When wood is not completely burned, a complex mixture of gases and particles is created and emitted as wood smoke. In EPA-certified stoves, most of the wood is burned, resulting in more heat for the home from the same amount of wood. EPA-certified wood stoves are designed with better insulation and improved airflow, which promotes more efficient combustion. This overall improved combustion process reduces the risks of producing pollutants from incomplete combustion, which could leak from the appliance itself directly into the indoor environment. Additionally, as more gases and particles are burned inside the stove, less smoke and fewer chemical and particulate pollutants are emitted from the vent stack or chimney into the ambient outdoor atmosphere. This helps improve outdoor air quality and reduces the amount of pollutants that could be drawn back into the home (or neighboring homes) through imperfect air barriers or other openings in the building envelope.
EPA maintains and periodically revises the list of EPA-Certified and EPA-Qualified wood-burning appliances to help housing professionals and homeowners make better purchasing decisions. The listed models have been tested and shown to burn cleaner and more efficiently than other, similar models. Any wood stove or fireplace that meets the requirements of the EPA Certified or EPA Qualified designation are identified with metal tags. See the References/Additional Information section below for lists of EPA-certified wood stoves and EPA-qualified wood hydronic heaters and wood fireplaces.
The Washington State Department of Ecology publishes more information about wood stoves along with a list of wood stoves compliant with Washington state standards.
How to Test for Proper Ventilation of Natural-Draft Fireplaces
- 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.
- 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.
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.
No climate specific information applies.
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 (Version 3/3.1, Revision 08), Rater Field Checklist
10. Combustion Appliances
10.2 Fireplaces located within the home’s pressure boundary are mechanically drafted or direct-vented. See Footnote 57 for alternatives.54, 55, 57
(54) 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.
(55) Per the 2009 International Mechanical Code, a direct-vent appliance is one that is constructed and installed so that all air for combustion is derived from the outdoor atmosphere and all flue gases are discharged to the outside atmosphere; a mechanical draft system is a venting system designed to remove flue or vent gases by mechanical means consisting of an induced draft portion under non-positive static pressure or a forced draft portion under positive static pressure; and a natural draft system is a venting system designed to remove flue or vent gases under nonpositive static vent pressure entirely by natural draft.
(57) Naturally drafted fireplaces are allowed within the home’s pressure boundary if the Rater has verified that the 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. If the net exhaust flow exceeds the allowable limit, it shall be reduced or compensating outdoor airflow provided. Per ASHRAE 62.2-2010, the term “net rated exhaust flow” is defined as flow through an exhaust fan minus the compensating outdoor airflow through any supply fan that is interlocked to the exhaust fan. Per ASHRAE 62.2-2010, the term “occupiable space” is defined as 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. See Footnote 43 for the definition of “habitable spaces”.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
This standard by the National Fire Protection Association provides guidelines for construction projects involving chimneys, fireplaces, venting systems, and solid fuel-burning appliances.
Federal emission standards established by EPA as required by Section 111 of the Clear Air Act. These standards set limits for source categories that cause or contribute significantly to air pollution. These standards are intended to promote use of the best air pollution control technologies, taking into account the cost of such technology and any other non-air quality, health, and environmental impact and energy requirements.
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.
Wood-burning fireplaces should have doors with gaskets and should have outdoor combustion air.
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.
Wood-burning fireplaces should have tight-fitting flue dampers and should have outdoor combustion air.
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.
Proper Ventilated Fireplaces = Ventilated Fireplace