Venting of Flue Gases (2023)

BOARD POLICY
ROLES OF INDIVIDUALS RESPONSIBLE FOR THE INSTALLATION OF VENTING OF FLUE GASES FROM GAS FUELED APPLIANCES
(enacted 10-25-2006)
(amended 05-29-2013)


The Board of Examiners of Plumbers and Gasfitters (the "Board") voted today to adopt and issue the following interpretation of the provisions of Chapter 142 of the Massachusetts General Laws and the Board’s regulations as found at 248 CMR relative to the licensure necessary to engage in the venting of flue gases from gas fueled equipment. This interpretation is intended to serve as an educational resource for local plumbing inspectors and for licensed plumbers and gasfitters.

The Board has adopted this interpretation following consultation with and the advice of Board Counsel. In light of the recent enactment of legislation requiring carbon monoxide detectors in residential dwellings, and the carbon monoxide poisoning incidents which resulted in the enactment of that legislation, the Board has issued this interpretation.

PURPOSE:

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To clarify and interpret the Board’s regulations regarding the roles of the individuals responsible for the installation of the venting of flue gases and associated with the installation, operation, repair or maintenance of gas fueled appliances.

INTERPRETATION:

The Board’s regulations at 248 CMR 3.05(1)(b)8, state that permits to perform gas fitting work shall only be issued to licensed plumbers or licensed gas fitters.

The complete installation, alteration, replacement or repair of gas fueled equipment requires that the licensed plumber or gas fitter provide for the proper venting of any gas fueled appliance in accordance with the regulations promulgated by the Board, the National Fuel Gas Code, NFPA 54-2002 and ANSI Z223.1-2002. The provisions of these regulations and codes are applicable to licensed plumbers or gas fitters. The licensed plumber or gas fitter is responsible for all aspects of the gas fitting work for which the permit is applied for and issued, including providing for the venting of the flue gases resulting from the operation of the gas appliance installed, altered, replaced or repaired in accordance with all applicable codes and regulations. The licensed plumber or gas fitter must be present for the final inspection of any installation, alteration, replacement or repair of any gas appliance, which includes the proper venting of such equipment. Final inspection will not result in an approval unless all regulations, code provisions and standards are complied with, including those related to the venting of flue gases.

Therefore, given that the regulations and code provisions for the installation, alteration, repair or replacement of gas fueled equipment, including the venting of the flue gases from that equipment, are enforced as against the licensed plumber or gas fitter to whom the permit for such work is issued, then only a licensed plumber or gas fitter or an appropriately trained person under the control and supervision of a licensed plumber or gas fitter can perform such work, specifically including the venting of gas fueled equipment in accordance with applicable regulations and code provisions.

Specifically, the venting of flue gases should be performed as follows:

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1. Large Boilers of 400,000 BTU/hr or more:
248 CMR 7.00 of the Massachusetts State Plumbing and Gas Fitting Code addresses Gas Utilization Equipment in Large Boilers (400,000 BTU/hr or more). Because of the size of the venting systems associated with Large Boilers of 400,000 BTU’s or more, it is the Board’s interpretation of its regulations in 248 CMR 7.00 that the vent connectors, vent connector manifolds, breeching, metal or factory built chimneys and or venting system associated with large boilers of 400,000 BTU/hr or greater may be installed by individuals qualified to assemble and construct combustion venting piping or conduits when the following conditions are satisfied;

a. A licensed (Master or Journeyman) Plumber or Gasfitter shall be responsible for and supervise the installation performed by such qualified individuals, and;

b. The supervising licensed (Master or Journeyman) Plumber or Gasfitter has secured a gas fitting permit in compliance with 248 CMR 3.00.

2. Gas Equipment under 400,000 BTU/hr:
248 CMR 5.00 of the Massachusetts State Plumbing and Gas Fitting Code addresses Gas Equipment under 400,000 BTU/hr. It is the Board’s interpretation of its regulations at 248 CMR 5.00 entitled Amendments and Modifications to ANSI Z223.1-NFPA-54, 2002 edition, that the vent connectors, vent connector manifolds, breeching, venting systems or special venting systems of gas appliances and gas equipment that is less than 400,000 BTU/hr may be installed by individuals qualified to assemble and construct combustion venting piping or conduits when the following conditions are satisfied;

a. A licensed (Master or Journeyman) Plumber or Gasfitter shall be responsible for and supervise the installation performed by such qualified individuals, and;

b. The supervising licensed (Master or Journeyman) Plumber or Gasfitter has secured a gas fitting permit in compliance with 248 CMR 3.00.

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3. Other:

It is the Board’s interpretation of its regulations that chimney lining systems, metal and factory built chimneys and for ventilation hoods used for exhausting combustion by-products and B-Vent, all as defined in NFPA-54, may be installed by individuals qualified to assemble and install such systems for gas appliances when the following conditions are satisfied:

a. A licensed Master or Journeyman Plumber or Gasfitter shall be responsible for and supervise the installation performed by such qualified individuals, and;

b. The licensed Master or Journeyman Plumber or Gasfitter has secured a gas fitting permit in compliance with 248 CMR 3.00.

DISCUSSION:

G.L. c. 142, § 1 defines "Gas fitting" as "any work which includes the installation, alteration and replacement of a piping system beyond the gas meter outlet or regulator through which is conveyed or intended to be conveyed fuel gas of any kind for power, refrigeration, heating or illumination purposes including the connection therewith and testing of gas fixtures, ranges, refrigerators, stoves, water heaters, house heating boilers and any other gas using appliances, and the maintenance in good and safe condition of said systems, and the making of necessary repairs and changes.” Emphasis added.

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G.L. c. 142, § 1 also defines "Master gas fitter" and Journeyman gas fitter." A master gas fitter is defined, in pertinent part, as "a gas fitter,…, who,…, performs gas fitting work, subject to inspection and in compliance of any law, rule or regulation pertaining to same." A journeyman gas fitter is defined as "a person who himself does any work in gas fitting, subject to inspection under any law, rule or regulation pertaining to same." Emphasis added.

In accordance with the above definitions, gas fitting work includes the "installation, alteration and replacement of the piping system” through which the fuel gas is supplied, but it is not limited to that aspect of gas fitting work alone. It also includes the maintenance in good and safe condition of gas piping systems. Gas appliance systems include the venting of flue gases, a potentially dangerous by-product of the system installed by the gas fitter or a qualified individual acting under the supervision of a licensed gas fitter. All gas fitting work, whether performed by a journeyman gas fitter or a master gas fitter, must be performed in compliance with "any law, rule, or regulation pertaining to same."

Under G.L. c. 142, § 13, the Board is authorized to promulgate rules and regulations relative to gas fitting in buildings throughout the commonwealth. The regulations are to be reasonable, uniform, based on generally accepted standards of engineering practice, and designed to prevent fire, explosion, injury and death. The proper venting of flue gases, including carbon monoxide, which are the by-product of gas fueled equipment installed by licensed plumbers or gas fitters, is addressed not only by the Board’s regulations, but also by the National Fuel Gas Code, NFPA 54-2002 and ANSI Z223.1-2002, the provisions of which have been adopted by the Board.

A licensed plumber or gas fitter is trained in the proper venting of flue gases in accordance with the aforementioned regulations, code provisions and standards, and is tested on his or her knowledge of those provisions before being issued a license.

A local inspector of gas fitting will inspect an installation, alteration, repair or replacement performed by a licensed plumber or gas fitter pursuant to a gas fitting permit issued by the local inspector to ensure that the licensed plumber or gas fitter has complied with those provisions. Only when the installation, alteration, repair or replacement has been determined to comply with all applicable regulations, code provisions or standards, including those applicable to the venting of flue gases, will the local inspector indicate his or her approval on the permit. Strict compliance with all regulations, code provisions and standards in the venting of flue gases by the licensed plumber or gas fitter is critical, as failure to comply with those provisions could result in serious injury from carbon monoxide poisoning to occupants of the building where the gas equipment is installed. It is for that reason that the venting of flue gases resulting from the operation of gas fueled equipment must be performed by licensed plumbers or gas fitters or, in the circumstances described above, by appropriately trained persons under their control and supervision.

FAQs

What is venting flue? ›

A flue is simply a passage for conveying exhaust gases from an appliance to the outdoors. A flue may be a duct, pipe, vent, or chimney. An unlined chimney is technically a flue, even though an unlined chimney is a fire hazard.

What is the difference between vent and flue? ›

Vents are similar to fireplaces and flues in that they may pass through other parts of the house and they do need temperature protection to prevent a transfer of heat from the vent to the surrounding building materials. However, vents are not designed to handle the high heat produced by wood burning fires.

What is difference between Category 1 and Category 3 venting? ›

Gas appliances are divided into four venting categories based on vent operating pressure and whether they are condensing or non-condensing. Category I is negative pressure, non-condensing. Category II is negative pressure, condensing. Category III is positive pressure, non-condensing.

Are flue gases harmful? ›

Flue gases contain a mixture of different compounds, many of which are dangerous for your health. One of them is carbon monoxide (CO), which can cause organ damage. Extended exposure to CO can be fatal.

Why is it called a flue? ›

Historically the term flue meant the chimney itself. In the United States, they are also known as vents for boilers and as breeching for water heaters and modern furnaces. They usually operate by buoyancy, also known as the stack effect, or the combustion products may be 'induced' via a blower.

How does a flue work? ›

The movement of hot gases rising from the fire creates a pressure difference between the inside of the flue and the room. This is called a “draught” and it forces air into the fireplace, this air feeds the flames as it rushes past the fire. The hotter the fire, the faster the air rises and the better the chimney works.

Why do you need a flue? ›

They Prevent Combustion in Surrounding Areas

Unlined chimney flues will allow smoke and gasses to pass through the bricks and mortar. Smoke and heat can eventually turn into a chimney fire and pass through to combustible materials such as wood studs and drywall, causing a house fire.

What is a gas flue on a house? ›

A gas flue is used to vent exhaust air from a combustion system, like the one on a furnace that burns natural gas or propane. A gas flue is a device used to vent exhaust air from a combustion system. These systems include things such as fireplaces and furnaces that burn natural gas or propane to produce heat.

What is flue gas HVAC? ›

Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced at power plants.

What are the two types of venting? ›

Active ventilation pulls the air in from the outside and pushes it out from the inside. Passive ventilation means the air in the attic is moved around by natural sources, such as wind. Both ventilation systems do their job, and one isn't better than the other.

What is class A venting? ›

Class A pipe is used to vent high-temperature exhaust released from wood, coal, and oil-burning appliances such as fireplaces, stoves, boilers, and furnaces. Not every venting system requires a Class A pipe, but it is absolutely necessary for use with all wood-burning fireplaces and stoves.

What is Category 4 vent pipe? ›

Category IV appliances use a fan to force the combustion gases through the vent piping. Because the fan creates a positive pressure within the vent pipe, any unsealed joints will allow flue gases to leak outward. Technicians must make certain that all joints are properly sealed and that there are no leaks.

How much CO2 is in a flue gas? ›

Typical flue gases from natural gas-fired power plants may contain 8-10% CO2, 18-20% H2O, 2-3% O2, and 67-72% N2; typical flue gases from coal-fired boilers may contain 12-14 vol% CO2, 8-10 vol% H2O, 3-5 vol % O2 and 72-77% N2.

Is there oxygen in flue gas? ›

Complete combustion is termed here when carbon and hydrogen in fuel is totally oxidized to carbon dioxide and water vapor, and no additional oxygen is present in the flue gases. This corresponds to air–fuel ratio of 10 in Figure 2.

How do you treat flue gas? ›

Flue gas treatment technologies are post-combustion processes to convert NOx to molecular nitrogen or nitrates. The two primary strategies that have been developed for post-combustion control and are commercially available are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR).

What does flue mean? ›

Definition of flue

: an enclosed passageway for directing a current: such as. a : a channel in a chimney for conveying flame and smoke to the outer air. b : a pipe for conveying flame and hot gases around or through water in a steam boiler.

What is a flue made of? ›

Flues can be made from terracotta clay, concrete, or stainless or galvanized steel. Clay and concrete flue sections (called tiles) are square or rectangular in cross-section; clay tiles are usually 24 inches long, while concrete tiles are shorter.

What is a flue system? ›

What Is a Flue System ? A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors.

How do you know if the flue is open or closed? ›

Feeling the breeze is another method you can use to know whether you have an open or closed flue. Locate your hand inside the fireplace and wait to notice if you can feel the air flowing. When the flue is open, air will flow down the chimney.

Which way does the flue open? ›

Some open the flue by rotating a knob in the anticlockwise or clockwise direction, while others require you to pull or push to open the flue. You can quickly tell whether you have an open or closed flue depending on the position of these controls.

Does gas fire need flue? ›

A regular gas stove does need a chimney or flue. As gas doesn't produce any heavy smoke, as a wood burning stove would, they don't require you to have a Class 1 brick chimney – though they usually can be installed into one of these without any issues.

Is a damper the same as a flue? ›

The flue is simply the open middle of the chimney that the smoke goes up. Dampers are sometimes miss-called flues or flutes, but they are something entirely different than the flue. A damper is intended to shut off- either fully or partially- the chimney flue.

Do you need a flue pipe? ›

The general rule is as follows: For a stove of up to 20kW a minimum of 6” diameter flue is needed. You can use a 5” diameter flue liner if you have a DEFRA approved stove and the manufacturer clearly states this is compatible.

How does a gas flue work? ›

The flue is simply a piece of pipework or duct that moves gases and hot air from the combustion chamber of the boiler to outside. With condensing boilers, the flue is effectively part of the heating system, as it is the heat from the burned gases that starts warming the returning water from the system.

How high does a gas flue need to be? ›

Flue terminals should also typically be sited at least 600mm above flat roofs. Boiler flues should be positioned at least 75mm below any material that could be damaged by heat, such as guttering. They should also be at least 150mm to the side of vertical drain or soil pipes.

How do I know what type of gas flue I have? ›

The best clue to knowing what type of flue you have is by simply looking at your roof and seeing what kind of outlet it has. Most of our gas fires are class 1, class 2 and precast suitable, however in the case of our wall mounted fires the requirements vary.

What is flue pipe in HVAC system? ›

What is a flue pipe? The flue pipe is a duct pipe that vents, or exhausts, gases from inside the home to the outside. A byproduct of combustion contains carbon monoxide and other dangerous compounds.

Where is the flue pipe located? ›

The furnace flue will usually be located on the top or the rear of the furnace. It will directly connect to a chimney or to a metal flue pipe that extends vertically to the roof. Most of the remaining pipe will be hidden as it passes through your home, though it may be visible in the attic.

What is the difference between fuel gas and flue gas? ›

The final gaseous product of combustion is then a flue gas. Fuels used for this purpose are mainly hydrocarbons (natural gas, coal, fuel oil, wood etc.)

What are the different vents? ›

There are three types of venting in your home: venting for supply air, return air and exhaust air. The effectiveness of these venting systems is facilitated by a combination of heating and air system materials, duct sizes, duct sealant and insulation.

What are the types of ventilation? ›

There are three methods that may be used to ventilate a building: natural, mechanical and hybrid (mixed-mode) ventilation.

What are the three kinds of attic ventilation? ›

Exhaust ventilation is most efficient when it's installed at or near the highest point of your roof where hot, humid air can easily escape.
...
Exhaust vents are divided into three common categories: static, powered, and mechanical.
  • Static Exhaust Vents. ...
  • Powered Exhaust Vents. ...
  • Mechanical Exhaust Vents.
Aug 18, 2021

What is Type C vent? ›

Type C vents are used only as connectors. They are single walled galvanized pipes, and as such often called “galvanized pipes”. They are used only for venting gas or oil. Using a C vent with solid fuel appliances can cause extremely toxic fumes. This is the least expensive of the pipes.

What is Category 3 flue pipe? ›

Category III is defined as a gas heating appliance with a flue loss equal or greater than 17% (non-condensing) with a positive vent static pressure. In a Category III venting system, if there is a leak in the venting system, flue gas will flow from the flue pipe into the space.

What category is B vent? ›

The AmeriVent all-metal, double-wall gas vent is listed as Type B by Underwriters Laboratories, Inc. and is approved for such residential and commercial applications as Category 1 water heaters, boilers, furnaces, space heaters, or wall heaters.

What does B vent mean? ›

B-vent fireplaces draw in air from inside your room to create combustion, then release the exhaust through a chimney in the roof of your home. These fireplaces are very similar to the installation of a wood-burning fireplace, but still run off of either propane or gas.

What 2 types of pipe can be used for a furnace flue pipe? ›

Suitable materials for the vent and condensate pipes include PVC (polyvinyl chloride), CPVC (chlorinated polyvinyl chloride), and ABS (acrylonitrile-butadiene-styrene) plastic pipe, depending on the furnace's specified exhaust gas temperature.

What is the code for venting a gas furnace? ›

503.6.

A gas vent shall terminate in accordance with one of the following: 1. Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 503.6. 5.

What is the purpose of a flue pipe? ›

The purpose of the flue pipe is to remove harmful byproducts of the combusted, or burned, fuel from inside your home. If the byproducts are not properly ventilated from inside the home, then you can have a dangerous buildup of carbon monoxide.

What is a flue on a water heater? ›

All water heater venting systems use a vent duct or pipe—also called a chimney or flue—to bring exhaust gases from the water heater to the outdoors. The duct may be metal or plastic, depending on the type of vent system.

What's a flue in a fireplace? ›

FLUE – (lining in a masonry chimney)- “A clay, ceramic, or metal conduit installed inside of a chimney, intended to contain the combustion products, direct them to the outside atmosphere, and protect the chimney walls from heat and corrosion.” Although building codes vary from one state or locality to another, the ...

Is a damper and flue the same thing? ›

A damper is located in the flue of your chimney. The flue is where the smoke escapes when the fire is going. Dampers are placed inside of the flue to help control ventilation. Your damper should have a chain or handle that you can access in order to open and close it.

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