Visual Evidence of Combustion Air Defects

Effects in buildings of inadequate combustion air:

This article describes the effects of inadequate combustion air in buildings and on building heating equipment. Simply visual clues such as soot deposits can give advance warning of potentially fatal carbon monoxide hazards, fire hazards, or equipment malfunction that means loss of heat or hot water.

Watch out: if you see chunks of soot at a gas burner such as shown in our page top photo the situation is very dangerous as there is a good chance of fatal carbon monoxide gas release in the building. Turn off the equipment and call for professional help.

This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters.

Combustion-Air-Related Heating Equipment Malfunctions & Their Implications

Here we list common ways that inadequate combustion air shows up in a building as malfunctioning heating equipment, noises, soot, odors.

Some of these conditions are dangerous.

• Noises & soot buildup 
  
  can lead to a potentially dangerous puffback which can damage the heating equipment and blow soot and smoke throughout the building.
  
  See SOOT on OIL FIRED HEATING EQUIPMENT
  and
  
  see GAS BURNER FLAME & NOISE DEFECTS
• Lack of adequate combustion air
  
  can result in improper system operation, sooting, loss of heat, noises, smoke, and potentially, the production of carbon monoxide or other flue or combustion gases which escape into the building - potentially dangerous
  
  Watch out: if adequate combustion air is not provided to an oil or gas burner, woodstove, fireplace or other fuel burning appliances, simply closing a door, opening an upper floor window, or turning on exhaust fans or a whole house fan can convert from a condition in which everything seemed OK to a dangerous situation with dangerous carbon monoxide production.
  
  See BACKDRAFTING HEATING EQUIPMENT

• Ignition transformer failure,
  
  Leaky oil at an oil burner ignition transformer an indicate a combustion air problem: watch for back pressure in combustion chamber -- watch out for blocked heating flue or blocked chimney - these would be unsafe, or the heater may be unreliable.
  
  An unreliable heater can lead to frozen burst pipes and costly building damage. A blocked chimney could lead to a potentially fatal carbon monoxide hazard.
• Heating System Odors,
  
  while carbon monoxide is odorless and colorless, when it is being produced by heating equipment it may be mixed with flue gases that indeed have a distinctive odor.
  
  Watch out: If you smell oil, gas, or other unidentified odors in a building, be sure that the safety of all heating equipment and chimneys is included in your investigation.
  
  See HEATING SYSTEM ODORS

• Unusual interior moisture conditions, noises, smoke,
  
  or odors during heating season--watch for blocked chimney or poor flue vent connections.
  
  For example, a blocked chimney at a gas fired appliance or inadequate combustion air can result in excessive moisture discharge (along with dangerous flue gas) into the building interior.
  
  Watch out: At UNLINED FLUE INSPECTIONS the rusty gas boiler top shown in my photo above is the heater discussed when we describe a near-fatality in Port Jervis New York.
  
  That serious hazard is also cited at HEAT EXCHANGER LEAK ALLOWED.  The chimney for a gas fired boiler became blocked.
  
  Once a gas boiler or furnace or water heater / calorifier has gotten up to normal operating temperature you should not feel flue gas spillage at the heater's draft hood. Be sure that chimney and heater repairs are performed by a qualified, certified expert.
  
  Watch out: A blocked chimney flue can give similar symptoms to blocked combustion air inlet: that is, most of the problems presented in this list.
• Equipment recalls:
  
  Specific heating system problem brands Repco, Blueray etc.
  
  [Do not confuse Repco™ heating boilers, which had fire chamber and other failures, with other products (REPCO pumps, REPCO controls, REPCO water conditioners, or water treatment that carry the Repco name.
  
  Those products are distinct from REPCO heating boilers and are produced/distributed by the R.E. Prescott Company.
  
  We are unaware of any remaining warranty or replacement support for failed or antiquated Repco heating boilers.]
• BACKDRAFTING HEATING EQUIPMENT
  
  - causes of flue gas spillage and explanation of the hazards
• BLUE vs YELLOW COMBUSTION FLAMES
  
  - the Blueray history and blue flame vs. yellow flame combustion, flame color & combustion efficiency, & how oil competes with gas as a heating fuel.

...

Continue reading at COMBUSTION AIR DEFECTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see this

Article BACKDRAFTING HEATING EQUIPMENTSeries Contents

• CARBON MONOXIDE WARNINGS: HOME HEATERS
• COMBUSTION AIR REQUIREMENTS
  • CLUES INDICATING INADEQUATE COMBUSTION AIR
  • COMBUSTION AIR DEFECTS
  • COMBUSTION AIR DEFECT EFFECTS
  • COMBUSTION AIR RULES of THUMB
  • COMBUSTION AIR vs ROOM SIZE
  • COMBUSTION AIR DUCT SIZE vs BTUh
  • COMBUSTION AIR for POWER BURNERS
  • COMBUSTION AIR INLET AUTOMATIC LOUVERS
  • COMBUSTION AIR INLETS vs COLD DRAFTS
  • COMBUSTION AIR SAFETY CHECK
  • COMBUSTION AIR SAFETY in MOBILE HOMES
  • COMBUSTION AIR for TIGHT BUILDINGS
  • COMBUSTION AIR for WOODSTOVES
  • UN-VENTED GAS HEATER SAFETY
• GAS BURNER SOOT CAUSE & CURE
• HEAT EXCHANGER LEAK ALLOWED.

Suggested citation for this web page

COMBUSTION AIR DEFECT EFFECTS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING SYSTEMS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Questions & answers or comments about combustion air requirements and safety hazards for oil and gas fired heating appliances

	HOME	ABOUT	ASK a QUESTION	CONTACT	CONTENT USE POLICY	DESCRIPTION	POLICIES	PRINT	PRIVACY
	© 2026 - 1985 Publisher InspectApedia.com - Daniel Friedman