Guide to Installing & Inspecting Draft Inducing Fans on Oil Fired Heating Equipment
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Draft Boosting Fans - Draft Inducers on Oil Fired Boilers, Furnaces, Water Heaters: inspection, installation
When to install a draft inducer fan
When does the presence of a draft inducer fan suggest something else is wrong?
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Here we discuss Draft Inducers or Draft Booster Fans installed on oil fired heating equipment.
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.
Our sketch at left, courtesy of Carson Dunlop, illustrates the three types of draft that may be found at chimneys and heating appliances: natural draft, induced draft by a fan blowing up a chimney, and forced draft by a fan blowing combustion air into a burner assembly.
This article discusses the use of induced-draft equipment.
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.
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.
The draft inducer fan shown in our photo was found in our garage of left-over stock from our heating service days. This model, the Tjernlund DJ-3 Draft Inducer Fan is sold by Tjernlund in St. Paul, MN, and the photo shows the essential parts of this draft inducer:
An electric motor (this one made by Fasco)
A blower assembly of fan blades driven by the motor and designed to project into a metal flue pipe or flue vent connector
An electrical junction box to connect the motor to the oil burner controls to turn the fan on and off when needed
A metal shroud around the fan assembly
The draft inducer fan motor and wiring need to be adequately protected from the heat of the oil burner combustion gases, that's why you wouldn't try to make one of these at home out of an old computer fan or stereo system fan.
When is it not appropriate to install a draft inducer fan?
Be careful; it would be a mistake and possibly dangerous to install a draft inducing fan to boost oil burner draft to solve a venting or backpressure problem before the cause of that problem is accurately diagnosed.
For example, if the oil fired appliance draft is poor because the chimney is blocked, or because the appliance itself is blocked with soot and debris, or because there is inadequate combustion air, the draft inducer fan might make the problem seem to go away, but at the risk of creating unsafe conditions in the heating system.
In our photo of an oil fired heating boiler has a draft inducer fan installed. The draft boosting fan is that mechanism you see on the under-side of the flue vent connector to the left of the boiler.
If this boiler is venting into a chimney that is really right at the wall where the flue vent connector enters the block wall, it's a very short flue run and we would not expect a draft problem. Something must be seriously wrong with the boiler or with chimney itself to have induced the technician to install a draft inducer fan on this heating system.
When Might We Need to Install a Draft-boosting Draft Inducer Fan?
But where the flue vent connector run-length is abnormally long or tortuous it may be difficult to get good draft, or where the chimney size itself (to which the flue vent connector joins) is too big or too small, the use of a draft inducer might be permitted. Check with the fan manufacturer and a qualified HVAC service technician before asking that one of these fans be installed.
In the photo shown here we have a long metal flue run - we cannot see the end of it, and the flue is shared, and there is no barometric damper installed - we suspect there is poor draft at this installation.
We've installed draft inducer fans in a few cases where the building chimney design was just too difficult to get good venting by natural draft.
For example we encountered a 12' long horizontal chimney run through masonry placing the boiler too far from the vertical chimney flue for good draft.
But in general, before installing a draft inducer we should make sure that the chimney is safe, not blocked, and that the heating equipment has been properly serviced and adjusted first.
You might discover that someone simply left open the ash pit door on a heating system's chimney - all that may be needed to improve the draft could be closing that little door!
At the chimney cleanout shown here we see a bit of debris that has collected at the bottom - which could be normal depending on what flue is being served and how long since the chimney was cleaned.
But if leave this door open not only do you nearly eliminate the chimney draft needed by the heating equipment, you are also creating a fire hazard, a fire spread between floors hazard, and a possible point of release of combustion gases into the building.
Close the little door.
How is a draft inducer fan installed?
A rectangular opening is cut into the metal flue pipe at a suitable location - usually close to the heating equipment since that makes wiring easier. The draft inducing fan comes with a paper template showing the size of the opening to cut.
The fan is mounted to the opening on the metal chimney or flue pipe so that its blades project into the flue, and so that when the fan motor runs it's pushing exhaust air away from the heating equipment and towards the chimney.
We've seen people install these fans in fireplace chimney flues in an effort to improve a fireplace that has inadequate draft, but we can't say if the manufacturer would approve that installation. There may be hazards due to creosote and other deposits from a wood-burning fireplace when one of these fans is used.
A note from Tjernlund informs us that draft inducer fan model DJ-2 has been replaced by Model DJ-3 and that all references in instructions to DJ-2 fans apply to DJ-3 models too.
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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.
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,
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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