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CHIMNEY INSPECTION DIAGNOSIS REPAIR
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FIREPLACE Damage & Unsafe Hearths - Settlement
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ChimScan: Inspecting Flues by Cameras
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Exceptions: Shared Flues Permitted?
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Combination Wood Burning Boilers, Furnaces, Fireplaces, Woodstoves
ChimAPedia ©
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- How do we inspect and diagnose problems on combination wood and oil-fired heating boilers and furnaces?
- Special chimney and draft regulation steps to take with combination fuel heating systems
- How thermostats control a wood fired heating system
- What happens when the draft regulator is set for burning wood and we switch to oil heat?
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Our site offers impartial, unbiased advice without conflicts of interest.
We will block advertisements which we discover or readers inform us are associated with bad business practices,
false-advertising, or junk science. Our contact info is at
inspect-ny.com/appointment.htm.
This article describes combination or multi-fuel heating boilers that combine burning wood with oil. We explain how a multi-fuel heating system works and we list the special considerations that such equipment needs such as attention to combustion air supply, draft regulation, combustion chamber design and cleaning, and general safety.
This website provides detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed. As with most inspection and safety topics, this material may be incomplete.
© Copyright 2008 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.
Combination Wood Burning Boilers, Furnaces, Fireplaces, Woodstoves - Special Considerations
Especially as oil prices have increased dramatically in the past few years and given the 2008 Bush Presidency economic crisis, many homeowners have a renewed interest in alternative heating energy sources.
Where firewood is available and economical, wood fired heating boilers and furnaces, and combination wood and oil heating systems that were first popularized in the 1970's oil embargo crisis have renewed interest.
Here we describe wood heat sources and special considerations in operation and safety of combination fuel wood and oil heating boilers and furnaces.
For a current comparison of the relative costs per BTU of heating oil, natural gas, firewood and electricity, readers should see HEATING COST FUEL & BTU Cost Table. Also see How to Reduce Home Heating Costs - Heating Cost Savings Tips where we provide expert advice on how to significantly reduce your home heating |
Combination Wood & Oil Boilers & Furnaces
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[Text in process] [Illus CD 1011-1021] [DF Photos - combination unit, woodstoves, coal stoves]
- single combustion chamber wood furnace - components, characteristics, where to locate, combustion air concerns.
- how wood or combination units regulate draft
- forced draft combustion system
- dual combustion chambers, different service requirements, different operating requirements
- draft control
- barometric damper inspection
- heat exchanger design
- heat content comparison: wood, gas, oil
Regarding concerns for chimney flues shared between oil and wood fired heaters, see Exceptions: Shared Flues Sometimes Permitted and Wood & Oil Fired Heaters
Also see WOOD STOVE SAFETY and Wood burning Fireplace Roof Clearance.
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Here are the basic components of a wood-only warm air furnace, compliments of Carson Dunlop.
Furnace inspection, diagnosis, and repair are discussed in detail at FURNACES, HEATING, and FURNACE CONTROLS & SWITCHES, and at DUCT SYSTEMS.
Many of the components on a wood fired warm air heating system such as ductwork and the blower assembly are the same as on oil or gas fired furnaces but the heating system itself is quite different:
- The combustion chamber location and construction are constructed to withstand a wood fire
- The heat exchanger may be simplified, with fewer passages to reduce soot and creosote clogging
- The wood fire burns continuously (rather than like a gas or oil burner that turns on and off in response to temperature controls).
- A back up heat source is usually provided either as a separate heating system (oil, electric, or gas). Controls on that heating equipment are designed to keep it turned off when the wood furnace is in operation. The backup heat lets the occupants leave the building without fear of total loss of heat (and frozen pipe damage).
Kerosene heaters: Our photo (left) shows a kerosene heater which an owner was using as their alternative heat source. It did not prevent pipes from freezing in a remote corner of the building when the central heating was inoperative, and we also were concerned about the adequacy of its fire-clearance distances.
- Combustion air is regulated to adjust the fire and thus the heat output of the wood furnace. Temperature controls in the occupied space and on the wood burning furnace adjust the combustion air flow in to the combustion chamber as the primary means of controlling the fire size and thus the heat output of the system. We discuss the wood furnace combustion air damper in more detail below.
- Firewood: Unless your system uses a processed wood fuel such as a wood pellet stove, heating fuel (firewood) is added by hand by the occupants as needed by opening a combustion chamber door.
- Ashes from burned wood are also removed manually by the occupants by opening an ash pit cabinet door.
- Pellet stoves feed processed wood pellets automatically from a feed hopper and thus require less frequent attention.
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Provide Combustion Air, Ventilation, Cooling Air for the Wood Furnace
Before looking in greater detail at wood fired furnaces and combination wood-oil furnaces, we and Carson Dunlop emphasize this safety note.
Because a wood-fired furnace operates at high temperatures and needs lots of combustion and cooling air it should not be located in a confined space.
Otherwise the risk of fire or improper operation are increased.
Chimney inspection and cleaning will need to be frequent to reduce the risk of a chimney fire as well. Sketch courtesy of Carson Dunlop. |
How the Wood Furnace Combustion Air Damper Works.
Sketches courtesy of Carson Dunlop.
Forced draft wood furnace operation: As the sketch (left) shows, instead of relying on natural draft, a forced-draft combustion wood air furnace uses an electric blower fan to feed air to the wood fire.
Heater controls can turn off the blower fan and on some models adjust the airflow rate as needed. |
Wood Furnace combustion chamber details
Wood Furnace combustion chamber cleaning details are shown in the sketches at left and below, courtesy of Carson Dunlop. |
Wood Furnace barometric damper inspection
DRAFT REGULATORS - 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 inspection requirements such as assuring that the damper is level, properly located, and operating freely are provided in our heating section at DRAFT REGULATORS - barometric dampers
The equivalent draft control on gas fired heating systems is discussed at Furnace Draft Hood on gas fired equipment.
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.
CHIMNEY INSPECTION DIAGNOSIS REPAIR
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Chimneys Cleaning Advice, Procedures
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Chimney Inspection Checklist
Chimney Inspection Indoor Procedures
Attic Chimney Inspection
Chimney Inspection Outdoors From Ground
Chimney Crack Detection & Diagnosis
Chimney Inspection Outdoors From Ground
Chimney Height & Clearance
Chimney Inspection Outdoors at Rooftop
Chimney Cap & Crown Inspection
Chimney Types & Materials
Chimney Cleanout Doors
Fire Clearances for Masonry Chimneys
Fire Clearances for Metal Chimneys
Fire Clearances, Single-Wall Metal Flues
Flue Sizing of Chimneys
Fire Stopping Between Floors
Flue Vent Connectors - Boilers, Furnaces
Chimney Inspection: Flue Interiors
Metal Chimneys & Flues
Shared Chimney & Shared Flue Hazards
Fireplace Damage & Unsafe Hearths - Settlement
Moisture Problems Damage Chimneys
Wood Burning Heaters Fireplaces Stoves
Coalstove Safety
Dead End Flues - Dead Base Chimney Hazards
Fire Clearance Safety Hazards
Fire stopping at Chimney Passage Through Floors
HEATING COST FUEL & BTU Cost Table
Woodstove Safety
Technical Reviewers & References
Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to
the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.
- Daniel Friedman - principal author/editor of the InspectAPedia TM Website
- 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.
- Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
- Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
- Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
- Chimney Building Codes and Chimney, Flue, and Appliance Venting Standards
- NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
- NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
- GAMA -
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
- National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
- Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
- Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
- New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
- New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
- "To Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
- Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
- "Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
- "Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
- "Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
- Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
- US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
- Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
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