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Combination Wood Burning Boilers, Furnaces, Fireplaces, Woodstoves ChimAPedia © 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?

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 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.

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

[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.

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.

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.

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.

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• Additional technical contributors & reference sources for this article are listed below.

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CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEY INSPECTION & REPAIR GUIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
Chimneys Cleaning Advice, Procedures
Chimney Cleanout Doors
Chimney Crack & Collapse Risks, Repairs
Chimney Draft & Performance
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

• 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:
• "Top 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: inspect-ny.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

Books & Articles on Chimney Inspection, Testing, Diagnosis, & Repair

• Books, Complete List of Fireplace & Chimney Design, Inspection, Repair Books at the InspectAPedia Bookstore.
• Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
  The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
  Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
• Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
• Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
• Fireplaces, a Practical Design Guide, Jane Gitlin
• Fireplaces, Friend or Foe, Robert D. Mayo
• NFPA 211 - Standards for Chimneys & Fireplaces, NFPA
• Principles of Home Inspection: Chimneys & Wood Heating (Principles of Home Inspection), Carson Dunlop
• Woodstove & Fireplace Maintenance & Safety, L. L. Helwig

More Information on Building Diagnostic Inspections and Repairs

• NFPA 211 - 3-1.10 - Relining guide for chimneys
• NFPA 211 - 3-2 - Construction of Masonry Chimneys
• NFPA 211 - 3-3 - Termination Height for chimneys
• NFPA 211 - 3-4 - Clearance from Combustible Material
• NFPA 54 - 7-1 - Venting of Equipment into chimneys
• Brick Institute of America - Flashing Chimneys
  Brick Institute of America - Proper Chimney Crowns
  Brick Institute of America - Moisture Resistance of Brick
• American Gas Association - New Vent Sizing Tables
• Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
• National Chimney Sweep Guild - Yellow Pages of Suppliers

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