Guide to Zone Dampers for Warm Air Duct Controls
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Ductwork Zone Dampers & Airflow Controls - Hot Air Heat & Air Conditioning Troubleshooting & Repair Guide
How to balance air flow in an HVAC system for heating or air conditioning
Manual duct balancing valves & automatic zone damper controls
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Here we discuss manual and automatic heating and air conditioning ductwork Zone Dampers & Airflow Controls used to control airflow through heating or cooling ductwork.
This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs.
Ductwork Zone Dampers & Airflow Controls - Hot Air Heat Troubleshooting & Repair Guide
Manual Air Conditioning or Heating Duct Zone Controls
Manual heating or air conditioning zone dampers are mechanical doors that are manually (by hand) open or closed in order to control the amount of warm or cool air flowing to a particular room or area in a building. By totally or partially closing the damper door, the owner or occupants of the building can balance the flow of conditioned air into various areas.
Because it can be tough for a new owner of an older home to even imagine, much less find where these duct air flow balancing controls are located, we include more photographs of what a manual duct air flow damper control lever might look like.
A manual zone damper or heating duct damper or cooling duct damper is particularly valuable in balancing air flow in buildings whose HVAC system includes long duct runs to some areas and short duct runs to other areas. If we take no steps to balance the air flow among building areas, when the blower fan is running, the rooms closest to the blower will receive the most air flow and more distant rooms can be difficult to heat or cool.
How do I Set the Duct Damper Handle - in What Position?
In general, the handle of the duct airflow control lever or damper is parallel to the damper itself, so if the zone airflow control handle is across the duct it is closing off air flow.
If the duct damper handle is parallel to the direction of the ductwork the damper is (probably) open.
But if airflow control doesn't seem to work as predicted, some further checking is in order, since it's possible to mount the duct damper handle improperly.
The photo at left shows the duct damper handle turned parallel to the direction in which this old (asbestos-paper covered) heating duct runs, so this airflow damper is in the "open" position.
As we show here, an alternative to manual heating or cooling air zone dampers is the use of mechanical louvers that can be opened or closed at individual supply air registers.
But when an air duct serves multiple rooms in a building, and when we wish that entire area to receive more or less air flow compared with other building areas, it is simpler and more reliable to use a duct damper or zone damper to control the each heated or cooled area at once.
Automatic Heating or Air Conditioning Zone Damper Controls
Photos of automatic zone damper controls wanted - Contact Us
What is an automatic duct damper and how do they work?
Automatic heating or air conditioning zone dampers are mechanical doors that open or shut under thermostatic control to provide individual area or heating or cooling zone control in buildings served by a single warm air heater or central air conditioner. In response to individual room thermostats the damper opens to permit conditioned air to flow into that room or building area when needed.
An automatic duct damper is 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.
The duct damper is located in an air duct and blocks the flow of warm or cool air into building rooms. It has nothing to do with venting flue gases up a chimney.
Our photo shows a motorized zone damper or air duct zone control produced by TrolATemp® a producer of automatic heating system controls. This unit is an automatic opposed-blade duct damper.
Here is a commercial automatic air supply register control which contains a booster fan as well.
You can spot an automatic zone damper on duct work by noticing that there is an external motor mounted on the ducts in one or more locations.
When heating or cooling are not needed in that building area or zone, the duct damper remains in the closed position.
Our photo shows a commercial duct damper in a New York City office building. In this case the damper is controlling airflow out of a supply duct into a single ceiling supply plenum and register.
What is an Automatic Fire Damper in Ductwork and how do they work?
A fire damper is required in air conditioning and heating ducts in some commercial installations and possibly by local residential building codes in some jurisdictions.
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".
A fire damper and the air ducts where it is installed would typically be located to stop fire spread between floors or other sections of a building, and it would be constructed of fire resistant materials. Think of an automatic fire damper as something like a "fire door" in a building. It closes to prevent fire spread.
Photos of automatic fire dampers & controls wanted - Contact Us
Automatic flue dampers, thermostatically controlled zone dampers, and fire dampers are compared and distinguished at DRAFT REGULATORS.
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Additional technical contributors & reference sources for this article are listed below.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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