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Here we discuss Draft Regulators or Barometric Dampers and we provide A Guide to Barometric Dampers on Oil Fired Boilers, Furnaces, Water Heaters: inspection, adjustment, cleaning, troubleshooting This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.

The articles at this website describe the basic components of a home heating system, how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs. We include product safety recall and other heating system hazards.

Details about draft control on oil fired heating systems (such as the oil fired heater shown in the photo above), including furnaces or boilers, are discussed right here at Draft Regulators barometric dampers on oil fired equipment. (Details about draft control for gas fired heating systems, including furnaces or boilers, are discussed at Furnace Draft Hood on gas fired equipment. Readers should also see CHIMNEY INSPECTION & REPAIR GUIDE and Flue Vent Connectors - Boilers, Furnaces for inspection, defect identification, and repair suggestions for chimneys and flues.

Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Guide to Inspecting Barometric Dampers or Draft Regulators on Oil Fired Heaters, Furnaces, Boilers, Water Heaters

Barometric dampers are devices used to regulate the draft on oil-fired heating equipment such as furnaces, boilers, or water heaters. The barometric damper or draft regulating device we are discussing here is normally used only on oil-fired heating equipment, not on gas-fired equipment. The equivalent draft control on gas fired heating systems is discussed at Furnace Draft Hood on gas fired equipment. On oil fired equipment the barometric damper, or draft regulator is typically a round Tee inserted in the flue vent connector between the heating appliance and the chimney. The face of the tee contains a round "door" with an adjustable weight. The service technician adjusts the weight to control the swing or opening of this door which in turn controls the amount of excess air that can enter the flue and chimney when the oil burner is operating. The draft regulator in our photo is not working - and has been deliberately jammed - indicating that something else is wrong, probably a chimney problem or an oil burner operating problem: the technician was unable to get enough draft, so s/he defeated the regulator - this is not a good idea, as we'll explain below. For a detailed guide to inspecting draft regulators and barometric dampers please see How to Inspect a Barometric Damper.

Why we need the Barometric Damper or Draft Regulator on a Boiler or Furnace

During oil burner operation, air moves into the oil burner and combustion chamber (as combustion air) and continues onwards as combustion gases moving out of the combustion chamber, up through the boiler or furnace heat exchanger and on to the chimney where these gases are vented outside. The force with which this air or combustion gas moves is the "draft" inside of the heating appliance.

Where Do We Measure Chimney Draft & How Much Draft do we Want at an Oil Burner Fired Heating Boiler, Furnace, or Water Heater?

Normally we measure draft at two locations: over the fire or in the combustion chamber where typically we may see -0.02 to -0.03 inches of water column pressure, and in the breech or at the stack pipe (properly, the flue vent connector) measured just a few inches above the boiler or furnace top, and before the barometric damper itself.

Notice that we're using negative numbers for draft measurement - that's because gases in the flue are moving up, up, and away, like superman, and onwards out of the building - away from the heating equipment. The gas pressure in the chimney needs to be less than atmospheric pressure in the boiler room for gases to leave.

This sketch of a barometric damper used on oil fired heating equipment (heating boilers or water heaters) is provided courtesy of Carson Dunlop.

In the breech we want to see about -0.05 inches WC pressure. If the breech draft is too low the combustion process and venting process may be inadequate, and if the draft measured in the breech is lower than the draft measured over the fire, the oil burner and combustion chamber are operating under pressure - which is often a problem on residential heating systems since few of them are designed to work this way. Thanks to L. Steinke for correcting our WC pressure data.

We do not measure draft in the flue vent connector past the barometric damper since the damper is regulating the draft and we're not seeing what the oil burner is seeing at the fire. Lots of companies make draft gauge measurement devices, including Bachrach™, and including nice little pocket units that anyone can carry.

In sum the draft we typically see on oil fired heating equipment is

• - 0.02" to 0.03" water column (w.c.) in the combustion chamber just over the fire
• - 0.04" to 0.06" w.c. in the breech - the flue pipe area between the top of the boiler and the bottom of the barometric damper. Some oil burner models require higher draft than these numbers, and other oil burner models are actually tolerant of back-pressure in the combustion chamber (positive draft, or draft in the "wrong" direction").

In the heating industry, traditionally draft measurements around -0.02" w.c. are considered "low", and around-0.06" w.c. are "high" draft levels.

How a Barometric Draft Control Works

It's simple, as Carson Dunlop's sketch above shows. The service technician measures draft over the fire and in the breech, and she moves a little weight on the hinged barometric damper door to cause the door to open wider or less wide to let more or less room air into the chimney as needed.

As long as the gas pressure inside of the flue and chimney is less than room air (that is, it's "negative" as we explained below), air from the room wants to enter the chimney through the barometric damper opening. Like the Goldilocks and the Three Bears, there are three possibilities:

1. The draft as sensed at the barometric damper is too strong (maybe a wind is blowing over the chimney top, increasing the draft): in this case the draft inside the flue, at the breech at the draft regulator is more negative - maybe -1.2 " w.c.. Since the air in the room is at normal pressure it will be stronger than the pressure inside the flue, so air in the room will push the draft regulator door "in" and make it open, letting room air flow into the chimney until, balanced by the setting of the weight on the moving draft regulator's door, the incoming room air enters the flue in enough volume to drop the draft pressure back to its desired setting, maybe to -0.04" w.c.
2. The draft as sensed at the barometric damper is too weak (maybe a wind is blowing down the chimney flue because we left off our chimney cap): in this case the draft inside the flue, at the breech and thus at the draft regulator is less negative, maybe -0.01" w.c. than we wanted - we're having trouble sending those flue gases up the chimney. The little weight on the draft regulator door causes the door to close, reducing the inflow of room air into the flue, and thus increasing the draft in the flue back to the desired number, maybe to -0.04" w.c. once again.
3. The draft as sensed at the barometric damper is just right: it's hovering where we set it at -0.04" w.c. In this case the barometric draft regulator is probably showing its little door a little bit open, with a little room air flowing into the flue. (Otherwise we wouldn't have any room to close the door to increase the draft when we need to do so.) And the draft in the flue is staying at the desired number, maybe -0.04" w.c.

How is the Barometric Draft Control Adjusted?

Why a draft regulator is needed:

While above we described how we measure draft inside of heating equipment and on the way to the chimney where (we hope) combustion gases are to be vented safely outside, the "draft" that the oil burner and furnace or boiler experience are not constant.

For example wind blowing over a chimney top can increase draft, as can a second appliance using the same chimney as the heater. Since the force of draft is not normally constant, and since we want the draft to be constant for optimum oil burner operation, the barometric damper is installed.

If the oil burner sees flue draft that is too low the combustion gases will not vent safely out of the building and the heating equipment may suffer from backpressure in the combustion chamber, causing overheating or other malfunctions.

If the oil burner sees flue draft that is too high combustion gases will vent out of the building just fine, but we're sending too much heat up the chimney by moving combustion gases too fast through the heater, thus we're sending our oil dollars up the chimney as heat rather than into the building as heat.

The service technician adjusts the barometric damper to maintain a continuous draft in the range we described above. Then if local conditions change, the barometric damper can open or close to let in more or less additional air into the flue and chimney, keeping the draft constant.

Are Barometric Draft Controls Used on Gas-Fired Equipment?

Incidentally, draft controls might be found on gas-fired heating equipment too, but the specifications are quite different. Gas fired heaters such as domestic gas fired furnaces are usually designed to operate at very low over-fire drafts - which means almost zero draft will be measured at the flue vent connections. That's why you usually don't see a hinged-door barometric draft regulator on gas fired equipment. Take a look at DRAFT HOODS - gas fired for details.

Field Corporation, and surely other draft regulator producers, provides different model draft controls for gas fired equipment, such as the Field Type MG1 and MG + MG2 regulators which use double swinging gates that open inward under normal up-draft conditions and outward in case of blocked flues, thus relieving internal pressures. Since improper venting of gas fired appliances easily produces very dangerous, potentially fatal Carbon Monoxide (CO), it is critical that these appliances are vented properly.

Do not ever install an oil-fired appliance draft regulator such as the Field Type AF shown here onto gas-fired equipment.

List of Defects & Signs of trouble with a barometric damper or draft regulator and what they mean

For a detailed guide to inspecting draft regulators and barometric dampers please see How to Inspect a Barometric Damper.

No draft regulator or barometric damper is installed: in this case the heater may work but it is impossible to tune it for optimum performance. We may be wasting fuel and money. The barometric damper is shared: if the damper is connected so that it is shared by two different heaters, say an oil fired furnace and an oil fired water heater, it is impossible to tune the system for optimum performance since the two appliances will prefer different adjustments each. The barometric damper is broken or missing parts: it cannot do its job and needs repair or replacement. The barometric damper is stuck or has been wired shut or covered with foil or tape: we love this clue. This is what a service tech does when s/he simply has been unable to get adequate draft for the oil burner. The tech thinks that since draft is always inadequate on this system there is no reason to let any air in at the damper. Well that's true, but we're treating the symptom, not the cause. The root cause might be, for example, a blocked chimney flue - which is unsafe and needs to be discovered and cleared. We've also see this silly "repair" when the underlying problem leading to inadequate draft was that someone had left the cleanout door to the chimney open. The barometric damper is stuck in the "open" position - usually due to a mechanical defect that is easily repaired, but sometimes because the weight has been misadjusted or lost. An always-open damper cannot properly regulate draft.

Barometric damper location: a barometric damper will work properly to regulate draft and reduce backdrafts in a variety of locations in relation to the heating appliance and the chimney. [Images at left are courtesy Field Controls.] Field corporation and other equipment manufacturers provide an instruction sheet with their product, showing the appropriate locations for a draft regulator. According to Field, "The control should be located as close as possible to a furnace or boiler and positioned as shown in [the figure at left]. The draft regulator should be 18" from a stack switch and at least 18" from a combustible ceiling or wall. Do not locate the draft regulator in a room separated from the appliance." If the draft regulator is not located properly it won't work properly and the heating system may also be unsafe. Further, if you see a draft regulator installed at the far end of a very long flue vent connector, say 12 to 25 feet or more, there is a more basic problem with excessive flue length and operating problems related to that condition, independent of the draft regulator. See FLUE VENT CONNECTORS for details. "The barometric damper should be adjusted (by adjusting the weight position) to maintain as low a draft as will give good combustion and meet the requirements for heat. The bracket is marked "Lo", "Med" and "Hi" which correspond to draft settings [if draft is measured inside the flue immediately before the regulator] of 0.2", 0.4", and 0.6" w.c."

Weight location & adjustment on barometric draft controls: the weight that is adjusted to regulate the operation of the draft control needs to be properly located as well as adjusted. T he weight location switches on most regulators depending on whether the regulator is installed on a vertical flue or a horizontal flue. Field ships their draft regulators with the weight installed in position for a vertical flue. The adjustment weight is in the right-hand slot when you are facing the control. If the damper is to be installed on a horizontal flue, the weight must be removed from the right-hand slot and attached to the left hand slot as shown in the illustration and sketches above. Thanks to boiler expert Dirk Faegre for suggesting these additional details.

Soot production or soot blow-back stains at the combustion chamber inspection port or burner mounting tube (or soot in general). Regardless of whether the draft regulator is serving an oil fired heating boiler or an oil fired water heater, soot coming out of the barometric damper or out of the flue vent pipe, or the presence of soot and burn marks on the heater, or even noises: stumbling, rumbling, noisy oil burners, as well as odors, are examples of improper oil burner operation that need prompt service. Our photo at left show an example of improper oil burner operation on an oil fired water heater: both systems show soot blow-out at the water heater's combustion chamber inspection port. Often these soot marks are a symptom of excessive pressure or "back pressure" inside the combustion chamber. Since this water heater is connected so closely to the chimney in a pretty new house, our first guess was that the water heater itself needed cleaning. Oil fired appliance sooting problems can be caused by an oil fired water heater or heating boiler that is way past due for cleaning (soot blocks the exhaust flue), by a blocked chimney, by improper draft regulator adjustment, or other defects. Share this Article       ... Technical Reviewers & References Search InspectAPedia Daniel Friedman - principal author/editor of the InspectAPedia® Website InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources. Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com. Additional technical contributors & reference sources for this article are listed below. Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. CARBON MONOXIDE/DIOXIDE CARBON MONOXIDE WARNING CHIMNEY INSPECTION DIAGNOSIS REPAIR CHIMNEYS & Flues - Asbestos Transite Pipe COOL OFF HEAT Thermostat Switch COMBUSTION AIR COMBUSTION AIR for TIGHT BUILDINGS COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ DRAFT REGULATORS - barometric dampers   Purpose of Barometric Draft Regulator what is a barometric damper and why do we need them   Measure Draft - how when where and why we measure draft and how we set the draft regulator   Barometric Damper Defect List   How to Inspect a Barometric Damper   Automatic Vent Dampers   Define flue damper, duct damper, & fire damper   Draft Inducer Fans Also see OIL BURNERS and OIL BURNER NOISE SMOKE ODORS "Instructions for Installing FIELD Type AF Barometric Draft Controls," Form No. 31 DC 30666, Field Corporation, Mendota, IL 61342 Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Lonny Steinke, Worland, WY USDA kindly corrected erroneous data we published on the proper draft numbers. - October 2008. Dirk Faegre, Camden, Maine (207) 232-9494 is a certified  BPI  energy auditor and certified Envelope technician who kindly suggested draft regulator and flue vent connector inspection defect additions 6 Sept 09

How to open and inspect a barometric damper for Inspection

Automatic Vent Dampers on Heating Equipment Flues

Draft Inducer Fans for Problem Chimneys & Vents

Draft inducers are special fans that are installed in the flue vent connector (or sometimes in the chimney) used to vent a heating boiler or furnace.

Most often we see these installed on oil-fired systems at which the technician was unable to obtain sufficient natural draft for proper oil burner operation.

If an oil burner lacks adequate draft, as we discussed above, it will not operate properly, leading to soot clogging, more costly heating bills, back pressure in the combustion chamber, and possibly unsafe heater operation.

We discuss draft inducer or "draft boosting" fans for heating systems (and maybe for some fireplaces) in detail at Draft Inducer Fans.

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

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".

You can see photographs of and read about fire dampers in ductwork at ZONE DAMPER CONTROLS .

What is a Draft Inducer Fan and how do they work?

What is a Barometric Draft Control and how do they work?

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

DRAFT REGULATORS - barometric dampers
  Purpose of Barometric Draft Regulator what is a barometric damper and why do we need them
  Measure Draft - how when where and why we measure draft and how we set the draft regulator
  Barometric Damper Defect List
  How to Inspect a Barometric Damper - how to look into the flue, what you'll see, what it means about heating system economy and condition
  Automatic Vent Dampers - how an automatic vent damper saves heating cost
  Define flue damper, duct damper, & fire damper
  Draft Inducer Fans - for solving draft and chimney problems

Also see OIL BURNERS and OIL BURNER NOISE SMOKE ODORS

• Dirk Faegre, Camden, Maine (207) 232-9494 is a certified  BPI  energy auditor and certified Envelope technician who kindly suggested draft regulator and flue vent connector inspection defect additions 6 Sept 09

More Information on Building Diagnostic Inspections and Repairs

• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• Dust from HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• 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
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• 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,
• 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

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