Guide to Zone Dampers for Warm Air Duct Controls
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What is a zone damper and how do they work on heating or cooling ducts?
Automatic Heating or Air Conditioning Zone Damper Controls
Manual zone dampers on duct work
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
Using an Air Supply Register as a Heating or Cooling Air Flow Damper or Control
How to use register booster fans to move heat between rooms
Questions & answers about how to find, adjust, & use automatic or manual HVAC air duct control s or zone dampers in heating & A/C ducts in order to balance heated or cooled air flow in buildings.

Automatic or manual HVAC air duct airflow controls: here we explain both manual and automatic heating and air conditioning ductwork zone dampers & airflow controls used to control airflow through heating or cooling ductwork. We describe how to find sometimes hidden manual duct dampers, and which way to set the duct damper lever to increase or decrease airflow through various sections of the ductwork and the building. We illustrate using air supply register controls to fine tune airflow in individual rooms or areas. We explain in detail automatic duct dampers and how they work. We also describe the use of individual airflow booster fans in the ductwork or in other locations to assure adequate cool or warm air supply in all areas.

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Ductwork Zone Dampers & Airflow Controls - Hot Air Heat Troubleshooting & Repair Guide

Manual Air Conditioning or Heating Duct Zone Controls

Also see BALANCING AIR DUCT FLOW where we discuss how to find and correct building conditions such as open suspended ceilings, windows, doors, etc. that foul up the proper distribution of conditioned air (heated or cooled) in buildings.

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.

But first you have to find all of the dampers - sometimes the ductwork or zone dampers are all located close to the furnace or air conditioner, but in some buildings there may be quite remote dampers. So if air flow is too much or too little in some areas of the building, in addition to checking for crushed or disconnected air ducts, look for a stealth-damper whose location may not have been immediately obvious - this means looking on all accessible sides of all surfaces of the ductwork. [Only a fool would have put a manual duct damper where you can't reach it, right?]

Manual duct damper handle (C) Daniel Friedman

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. At below left our red arrow shows the direction of warm air movement out of a supply plenum and into ductwork, and our blue line shows the position of the duct damper - blocking most but not all of the airflow.

Shown in another example at above right, 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. This damper is in the at about 80% open position.

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.

That is, the position of the duct damper handle also indicates the position of the actual damping baffle inside the ductwork.

If the duct damper handle is parallel to the direction of the ductwork the damper is (probably) wide open (photo at left).

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.

Using an Air Supply Register as a Heating or Cooling Air Flow Damper or Control

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.

Frequently Asked Questions (FAQs) about zone dampers and airflow register booster fans used in HVAC systems

Question:

Do you do a thermostat that i can put in my room when it gets to hot it will turn a fan on to take the heat into other rooms? - K.H.

Reply:

If you are asking if we can sell you a heating part the answer is no, sorry, but we do not sell anything. InspectAPedia.com provides building and environmental diagnostic and repair information. In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.

But we can tell you what you might want to install to address your heat distribution improvement question:

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with your heat or heating distribution system - something that might change how you want to "fix" a problem of uneven heat in the building. That said If you are unable to turn down the heat in a room that is too hot (by partly closing a radiator control valve, by installing a thermostatically operated individual radiator valve, or partly closing an air supply register)

You could indeed direct warm air from one room into another that is adjoining by the following procedure:

Purchase an air register booster fan - this is a fan-operated through-wall ventilating register - this looks like an warm air duct register cover that includes a small electric fan.
Mount the fan assembly in an opening cut near the ceiling on the wall between two rooms - one that is too warm and a second that is too cool. These systems often work using low-voltage motors and controls, powered by a separate power transformer and low voltage wiring - easy and less costly to run than a new 120V circuit.
In wiring the fan in this wall opening, install a thermostat that will switch the fan on or off as a function of room temperature. Alternatively, some air register booster fans include a remote control that will operate the register booster for you with no additional wiring.

With that set-up, when the overheated room reaches the set temperature on the new wall thermostat, that switch will turn on the electric fan that will begin moving warm air from the too-hot room to the too cool room. When the room temperature in the "too hot" room falls, the new wall thermostat will turn off the air moving fan.

Several companies make these air-moving registers and they come in a variety of sizes and colors such as

Airflow Breeze air movement register booster fans are produced by AirFlow Technology, Airflow Technology 1427 West 86th Street, Suite 328 Indianapolis, IN 46260 1-800-458-5540 website: http://www.aftproducts.com/Airflow_Breeze_3ff0ef340c6e0e13b.dept

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ZONE DAMPER CONTROLS - see detailed links at page left

Airflow Breeze air movement register booster fans are produced by AirFlow Technology, Airflow Technology 1427 West 86th Street, Suite 328 Indianapolis, IN 46260 1-800-458-5540 website: http://www.aftproducts.com/Airflow_Breeze_3ff0ef340c6e0e13b.dept

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
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 Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"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.)
Links to our list of additional information on heating system inspection, repair, maintenance
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Ductwork Zone Dampers & Airflow Controls - Hot Air Heat Troubleshooting & Repair Guide

Manual Air Conditioning or Heating Duct Zone Controls

How do I Set the Duct Damper Handle - in What Position?

Using an Air Supply Register as a Heating or Cooling Air Flow Damper or Control

Automatic Heating or Air Conditioning Zone Damper Controls

What is an automatic duct damper and how do they work?

What is an Automatic Fire Damper in Ductwork and how do they work?

Frequently Asked Questions (FAQs) about zone dampers and airflow register booster fans used in HVAC systems

Question:

Reply:

Questions & Answers regarding this article

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Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair