Draft Measurement Guide for Chimneys & Flues
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How & where do we measure the draft in a chimney or flue for heating appliances?
- What are the right or specified draft measurements we should see in a chimney or flue?
AUTOMATIC VENT DAMPERS - separate article
BACKDRAFTING HEATING EQUIPMENT & CARBON MONOXIDE - CO - separate articles
CHIMNEY DRAFT & PERFORMANCE - separate article
COMBUSTION AIR DEFECTS - separate article
COMBUSTION AIR for TIGHT buildings - separate article
COMBUSTION GASES & PARTICLE HAZARDS & COMBUSTION PRODUCTS & IAQ - separate articles
COMPLETE COMBUSTION, Stoichiometric - separate article
DIRECT VENTS / SIDE WALL VENTS - separate article
DRAFT HOODS - gas fired - separate article
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS - separate article
DRAFT REGULATOR SOOT INSPECTION - separate article
DRAFT INDUCER FANS - separate article
Questions & Answers about inspecting and adjusting the barometric damper or draft regulator on oil fired heating equipment
References

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This article explains the methods of measurement and proper adjustment settings for draft regulators or barometric dampers on oil fired heating equipment. This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

Where & How Do We Measure Chimney Draft or Heating Appliance Flue Draft?

Barometric dampers used on oil-fired heating appliances (furnaces, boilers, water heaters) are discussed in detail beginning at DRAFT REGULATORS, DAMPERS, BOOSTERS. 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 DIAGNOSIS REPAIR 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.

As we explain at our home page for this topic, DRAFT REGULATORS, DAMPERS, BOOSTERS, a barometric draft control, also called a "damper" or barometric damper, is a hinged, weighted door on an opening at a heating flue.

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.

Where do we Measure Chimney or Flue Draft & What is the Correct Draft Measurement at Oil Fired Heaters?

Draft regulator, barometric damper schematic (C) Carson Dunlop

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 Associates.

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. - for correcting our WC pressure data.

Draft measurement example (C) D Friedman

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.

Our photo (left) shows a traditional Bachrach kit draft measurement gauge in use (green arrow) and its connection to the flue vent connector at the top of a boiler (red arrow) that in this case had no barometric damper installed.

This boiler had a poor draft, a history of sooting problems and a too-short chimney that we were in process of replacing when these photos of draft measurement procedure were made.

At this New York home (photos just above and below) the draft in the breech was running at about -0.02" w.c. - it should have been at least twice that amount. At below left you can see that the draft was hovering around 0.02" and at below right you can see our connection of the draft gauge sensing probe into the flue vent connector just above the boiler top.

Draft measurement instrument (C) D Friedman

How Much Draft do we Want at an Oil Burner Fired Heating Boiler, Furnace, or Water Heater?

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").

Correcting Inadequate Chimney Draft - extending the flue height

Replacing a too-short chimeny with a proper one (C) D Friedman

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. After we replaced the too-short chimney with one of proper height, and with a draft regulator (barometric damper) now installed at the boiler top, our measurement showed that we had a good draft in the flue vent connector - almost 0.06" w.c. in the breech (photo above left). In our chimney replacement photo (above right) the new chimney extending 24" above the roof of a new addition (green arrow) is much taller than the original 20" chimney (red arrow). That's how we got good draft in the new chimney set-up.

What are the recommended draft settings at a draft regulator / barometric damper?

By moving a weight along a scale. You can see a weight and scale in our photo of the Field Type AF Draft Control.

In general the draft regulator is set to the lowest draft that gives good combustion and proper oil burner operation. Higher wastes energy.

While the heating equipment is operating at normal temperature, the draft is set to a number specified by the oil burner manufacturer, so we can only give approximate settings in this discussion. To find the proper weight setting to control the draft regulator, the heating service technician will make three measurements:

Draft over the fire (typically set to 0.02" to 0.03" WC over the fire)
Draft in the breech (always higher than the draft over the fire, and typically around 0.04 - 0.06" WC).
CO2 measurements (which tells us how complete is the heating oil combustion process) - adjusting the draft affects the rate of combustion air movement into the combustion chamber.

It is the position of the weight along a moveable scale, usually by screwing the weight in or out, or by sliding the weight along a scale (see our photo), that adjusts how far the draft regulator door will open in response to these three conditions described above. It's basically a principle of leverage -the weight is moved closer to or farther out from the axis of rotation of the moving draft regulator door.

So do not change the barometric draft control's weight setting unless you're a trained service technician who knows when, where, how, and why to measure draft at an oil fired heating appliance.

Weight location & adjustment on barometric draft controls

Draft regulator installation instructions (C) Field Controls - D Friedman

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.

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Frequently Asked Questions (FAQs) about measuring chimney draft

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

[1] "Instructions for Installing FIELD Type AF Barometric Draft Controls," Form No. 31 DC 30666, Field Corporation, Mendota, IL 61342, web search 04/02/2011, original source: http://www.fieldcontrols.com/pdfs/04592700.pdf, Field Controls, Kingston, North Carolina 28501, Tel: 919-522-3031
[2] Tjernlund Draft Controls, A Series (single action for oil, solid fuel, and fan-assisted gas burners) and B Series (double action for gas heating appliances), web search 04/02/1011, original source: http://www.tjernlund.com/Tjernlund_8500490.pdf , Tjernlund Products, Inc., 1601 Ninth Street, White Bear Lake MN 55110-6794, Tel: 651-426-2993 or 800-255-4208 website: www.tjernlund.com Email: fanmail@tjfans.com
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
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
Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
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.)

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

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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Draft Measurement Guide for Chimneys & Flues InspectAPedia® -