Photograph of a draft regulatorDampers & Dampeners in Buildings

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Types & definitions of HVAC duct & flue dampers, vibration dampeners, and fire dampers found in buildings.

This article defines and describes barometric dampers, draft regulators, automatic flue dampers, draft inducers, zone dampers, HVAC supply register controls, fire dampers, automatic fire and smoke dampers, fireplace dampers, and fresh air inlet dampers and controls.

We include photographs of each type of damper or dampener used in buildings or in building mechanical systems and we provide links to in-depth articles describing the choices, installation, inspection, troubleshooting and repair of all types of building and HVAC system air controls, dampers and dampeners such as automatic and barometric flue dampers used on heating equipment, coal stove, pellet stove, woodstove draft controls, draft inducer fans, HVAC duct air flow controls (manual register controls, duct dampers, zone dampers, automatic fire dampers, vibration dampeners), fireplace dampers, and fresh air supply dampers and controls.

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Dampers and Dampeners, types, definitions: of flue damper, duct damper, fire damper, a draft regulator& other dampers or dampeners

This article catalogs and describes all types of air and draft regulation devices used in buildings where control of heating appliances is needed.

Article Contents

Direct Vented Heating Appliances Don't Use a Barometric Damper

Direct-vented heating appliances that vent flue gases outside without using a chimney are typically operated by a power vent fan in or at the heating appliance. These vents don't use a barometric damper for draft regulation. See DIRECT VENTS / SIDE WALL VENTS

Definition of automatic flue damper

An automatic flue damper is a device (shown below) that closes the heating flue when the furnace or boiler is "off" so that we won't continue to lose building heat up the chimney - it's a device to reduce heating costs and save on heating oil consumption.

Photo of automatic flue vent damper (C) Daniel Friedman

When the heating system has turned off at the end of an "on" cycle of burning fuel, the automatic flue damper electric (see sketch above and photo at left) motor turns a baffle inside of the flue vent connector pipe to a position "across" the pipe so that the airflow inside the pipe is blocked or stopped.

Don't confuse an automatic flue vent damper with other "damper" devices: a heating system automatic duct damper or a duct fire damper or a heating zone damper.

Definition of Barometric Draft Control (also called Flue Damper) and they work

A barometric draft control, also called a "damper" or barometric damper, is a hinged, weighted door on an opening at a heating flue. The key difference between a barometric draft control or flue damper and an automatic flue damper is that the barometric damper operates by barometric pressure or natural draft while an automatic flue damper is operated by an electric motor.

Photograph of a draft regulator

The door opens or closes to let extra air into the flue to assure that the draft in the flue remains constant at the proper setting needed for proper heating system operation.

Coal stove draft control

Coal fueled heaters use manual dampers in the coal stove flue or for larger and automatically-fed coal fired boilers or furnaces the system may incorporate a thermostatically-operated automatic flue damper to control both draft and thus the system's heat output.

Coal stove installation by Daniel Friedman(C) Daniel Friedman Coal or wood burning stove installed by Paul Galow (C) Daniel Friedman

The coal stove shown at above left was installed by the author (DF) in the 1970's. A slider along the stove bottom permitted the user to adjust the air intake rate - a necessary combustion and heat control since the installation of this stove in front of a small fireplace gave no access room for a flue damper control.

The second fireplace-inserted heater at above right is a coal stove that was designed to also burn wood. This wood/coal heater, installed by Paul Galow in New York in the 1970's, also had a sliding air intake control and no accessible flue damper.

The vertical lines you see in the glass front of each of these coal burners allowed the installation of glass that would not fracture due to thermal expansion, allowing the occupants to enjoy watching the fire. Yes ultimately these get broken by a careless occupant or user, putting the stove out of use until the glass could be replaced.

Watch out: if the incoming combustion air cannot be shut down because of leaky coal stove gaskets or other damage like the broken glass in the coalstove door, the coal stove is unsafe as its burn-rate cannot be regulated.



Reader Question: can I put to barometric dampers on the same flue along with a manual one on my Alaska Channing III Coal Stove?

Alaska Channing III Coal Stove, USA Tel 570 387 0260 - permission use requested 2/1/15(Dec 14, 2014) Bill said:

I have a Alaska channing 111. My barometric damper is 6 in then [the flue vent connector goes to 8 in to connect ] to massonary chimney.

It seems I need two dampers. I installed a manual damper to help

My question is can I put 2 baro dampers in the same flue to control proper draft

Thanks, Bill



Watch out: I infer that you are getting too much heat or having trouble controlling your coal stove. This condition can be unsafe and in fact in extreme cases can cause a house fire.

See COAL STOVE OPERATION & SAFETY for detailed suggestions on solving this problem with your coal stove. There we repeat your question and answer it in detail.

Definition of Draft Inducer Fan and how do they work?

Draft inducer fan installed (C) Daniel Friedman

A draft inducer is a booster fan that increases the flow of combustion gases up a chimney. In our photo at above left you can see the black motor and bronze-coloured fan cage of a draft inducer fan mounted underneath the flue vent connector between the oil fired boiler and the concrete block wall that affords entry into a chimney (not visible).

Draft inducers are used when there is a problem with the chimney or heating equipment installation that prevents natural draft from working adequately.

We discuss draft inducer or "draft boosting" fans for heating systems (and maybe for some fireplaces) in detail

Definition of automatic duct damper or HVAC zone damper

Zone dampers are manual or electrical (thermostatically controlled) baffles that open or close in heating or cooling air ducts to control heating or cooling zones in buildings.

Details about zone dampers are

A motorized duct zone damper (C) Daniel Friedman

An automatic duct damper is a mechanical device (shown above), usually controlled by a room thermostat, which opens or closes a metal baffle inside of a warm air (or cool air) heating (or cooling) duct in order to provide multiple heating zone control in a building.

You can see photographs of and read about manual and automatic heating and air conditioning zone dampers

Definition of Manual Duct Dampers used in HVAC system ductwork

A manual duct damper, also referred to as a manual HVAC zone damper, is a hand-operated baffle that can be turned to open or close a heating or air conditioning supply duct to thus control the flow of conditioned air into a building area.

Our photo below shows a manual duct damper control handle on an older (asbestos-paper-covered) heating duct. When the handle long axis is parallel to the ductwork (our blue line) the air flow is fully open (the red arrow).

Manual air duct damper control (C) Daniel Friedman

Details about manual HVAC duct dampers are

Definition of Supply Air Register Damper

The most-common means of controlling heating or cooling air delivery out of an individual duct or zone is the opening or closing of individual supply air registers. A lever on the supply register grille permits opening or closing a baffle that controls air flow out of the duct system just at this individual register.

Air supply register in a floor (C) Daniel Friedman

Details about individual supply air register controls are at AIR REGISTER for ZONE CONTROL

Control of the entire duct zone is possible using a manual (DUCT DAMPERS, MANUAL) or automatic (DUCT DAMPERS, AUTOMATIC) duct zone control damper.

Definition of Automatic Fire Damper in Ductwork and how do they work?

A fire damper is required to prevent the spread of a building fire or smoke through air conditioning and heating ducts in some commercial installations and possibly by local residential building codes in some jurisdictions. Fire and smoke dampers are typically required in office buildings, health care facilities, and other commercial structures.

The automatic fire/smoke damper operates (usually) by automatically closing a door or doors within the damper on the detection of a temperature increase or by operation of a separate smoke detector.

Our photo at below left shows a pair of open fire damper doors in the ceiling of a commercial building in New York City. In event of a fire these doors are intended to be automatically closed. Similar dampers may be installed right in HVAC ducts where the ducts pass between different building areas.

Fire damper between sections of a commercial building ceiling used for return air (C) Daniel Friedman Dayton brand rectangular fire door shown in open position. (C) InspectApedia

More about the photo of ceiling return air plenum fire dampers shown at above left is at RETURN AIR REGISTERS & DUCTS

A fire damper might work similarly to an automatic duct damper, but its purpose is quite different: in the event that a fire is detected in a building or in its mechanical systems, (by heat or smoke or other means of fire sensing), the fire damper closes off the air duct to avoid spreading smoke or fire rapidly through the building. The fire damper is otherwise normally "open".

See photographs of and read details about automatic fire dampers and automatic fire/smoke dampers at AUTOMATIC FIRE DAMPERS

Definition of Duct Vibration Dampeners

Duct vibration dampers or properly called vibration dampeners are fabric joints placed in HVAC ductwork to prevent the transmission of vibration and noise from the air handler of a heating or air conditioning system into the ductwork and through the ductwork into the occupied spaces of a building.

Details about duct vibration dampeners are found at DUCT VIBRATION DAMPERS

Definition of Fireplace Damper

A fireplace damper is a metal door installed in the fireplace chimney throat. To avoid wasting building heat by sending it up the chimney when a fireplace is not in use, the fireplace damper door is closed when the fireplace is not in use. Our sketch below, provided by Carson Dunlop Associates and used with permission, shows the location of a fireplace damper in the chimney flue where a woodstove or fireplace insert has also been installed.

Fireplace damper sketch showing the location of the damper where a fireplace insert was installed (C) Carson Dunlop Associates, used with permission by

Details about fireplace dampers, their installation, inspection, repair, replacement, and defects are at FIREPLACE DAMPER DEFECTS, REPAIRS

Definition of Fresh Air or Outdoor Air Supply Dampers & Controls

Definition of fresh air or outdoor air supply control damper

Outdoor air or fresh air is supplied (or can be or often should be) supplied to combustion equipment such as gas or oil or other fuel fired heaters as well as to fireplaces or woodstoves. Outdoor or fresh air is also supplied to the HVAC duct or air delivery system to improve indoor air quality. Below we list articles describing these various outdoor air or fresh air supply controls.

Outdoor air supply intake register (C) Daniel Friedman

You can see photographs of and read about fire dampers in ductwork or read about strategies for managing building fresh air intake at

Kerosene Heater Draft Control

Our photo below shows a kerosene heater installed in an older New York Home. There is no visible draft control on this heater's flue. Instead the user regulates heat by controlling the fuel flow level.

Kerosene heater showing chimney flue conections (C) Daniel Friedman

[Text and illustrations are in process, text, comments, photo, contributions are invited. CONTA

Pellet Stove Draft Control

[Text and illustrations are in process, text, comments, photo, contributions are invited. CONTACT US]

Pellet stove certifications and fire clearances are given at FIRE CLEARANCES WOOD & COAL STOVES

Wood-Oil Combination Boiler or Furnace Draft Control

Wood Oil combination boiler (C) Daniel Friedman

The combination wood-oil fueled heater shown above regulates draft by a combination of means:

Input air and oil burner adjustments at the oil burner and a barometric damper regulate draft when the heater is being fired using heating oil (indicated in yellow)

A themostatically operated combustion air inlet regulates the wood fire when the heater is being fired using wood. In this mode a barometric damper may be replaced with a manual draft control or an automatic draft control in the exhaust flue between the heater and its chimney (green arrow 1, 2, 3, 4)

Using our photo as an illustration of the temperature and draft controls on the wood-side of the combination wood-oil heating boiler shown: [Click to enlarge any image]

Wood burning controls on the dual-fuel boiler:

The boiler temperature or burn rate for wood is set by turning the adjustable thermostat knob at upper right in the photo - green arrown #1.

The thermostatic control monitors the temperature in the combustion chamber / heat exchanger on the wood side of the boiler. A bimetallic spring lifts the air shutter control arm (green arrow #2) to pull the combustion air shutter control chain (green arrow #3) which lifts open (more air) or falls to close (less air) the combustion air intake door at the bottom right of the boiler (green arrow #4).

A barometric damper draft control on the heating flue is not shown.

Watch out: if the wood-oil boiler uses a single chimney and flue and a common barometric draft regulator on that flue for both fuels (unsafe, and illegal in some jurisdictions) it will not be possible to adjust the draft regulator for optimum performance of both fuels. There may also be creosote fire hazards when burning different fuels in the same flue.

Oil burning controls on the dual wood-fuel boiler:

In our photo of a dual fuel wood-oil boiler at above right, the yellow arrow 6 points to the primary aquastat and yellow arrow 5 points to a second high limit aquastat control. Combustion air for the oil burner is provided through the oil burner air shutter and by a squirrel cage blower fan in the oil burner. Draft will be regulated by a barometric draft regulator on the flue vent connector (not shown).

More details about how the combustion air damper and other controls on this wood-oil boile

Details about wood-oil combination fueled heating boilers and furnaces are

Wood Stove Draft Control

Wood stove showing manual flue damper (C) Daniel Friedman Jotul Woodstove installed by Paul Galow (C) Daniel Friedman

I'm not so sure the wood burning stove shown at left above is a fire-safe installation, but you can plainly see the manual flue damper handle (pointed-to by our blue arrow) in the rusty flue section about 30 inches above the top of the woodstove. When the damper handle's long axis is parallel to the flue the damper is in its fully open position.

Woodstoves also regulate the wood fire and thus stove temperature by adjusting the combustion air intake to the woodstove. At abpve right is a beautiful Jotul woodstove that I (DF) traded to Paul Galow for a fancy wristwatch. The orange arrow points to the woodstove air inlet draft control.

Watch out: if the incoming combustion air cannot be shut down because of leaky wood stove gaskets or other damage the wood stove is unsafe.

Paul has installed air-spaced heat shields of ceramic tile mounted on fireproof board behind the stove and he added a heat shield (the silver contraption) on the side of the stove facing a bed just to slow down the heat in that direction. Thst wood-box on the left side of the stove is a bit close in my OPINION but Mr. Galow is not much impressed by my caution.

Watch out: if the flue damper rusts or becomes damage it may be impossible to slow the chimney draft, resulting in an over-heating stove and possibly a chimney or house fire. Though questionable fire clearances and accumulated creosote may have been factors, just such a runaway wood stove fire and its disastrous results are illustrated

Details about wood stove installation, use and safety begin


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