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Mobile home furnace (C) Daniel FriedmanCombustion Air Safety Inspection Checklist
Gas-fired Residential Equipment Combustion Air Problems

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Checklist for heating equipment combustion air safety defects & hazards:

This procedure is only intended for buildings where LP gas or natural gas heating appliances (heating boiler, warm air furnace, water heater) are installed AND where a flue gas spillage safety switch such as a Tjernlund UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment or Field Controls Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches are installed on those appliances.

This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters. These articles answer most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. Our photo at page top shows an oil fired furnace installed in a closet with an airtight door; there was no outside combustion air supply. The heating system could not work properly nor safely in this home.



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Guide to a Simple Combustion Air Safety Check for Gas Fired Heating Appliances

Thanks to Tjernlund Products who recommended this procedure, we describe a simple combustion air safety check that can be performed by a homeowner or by a heating service technician.

Watch out: inadequate combustion air not only causes improper and wasteful operation of heating equipment it can also produce fatal carbon monoxide gas hazards indoors. The quantity of combustion air needed depends on the fuel type, the input BTUh rating of the heating equipment, and additional air needed to assure effective exhaust draft to carry combustion products safely out of the building.

This procedure is only intended for buildings where LP gas or natural gas heating appliances (heating boiler, warm air furnace, water heater) are installed AND where a flue gas spillage safety switch such as a Tjernlund UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment or Field Controls Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches are installed on those appliances. (Similar products are provided by other manufacturers.)

  1. Close all doors and windows of the building. If the gas fired heating appliance is installed in a utility room or closet, close the entry door to that room. Close all fireplace dampers. Turn on the clothes dryer (if installed) and all exhaust fans such as range hoods, bathroom exhaust vent fans, whole house fans, and radon mitigation fans, running all fans at their maximum speed.
  2. Turn on and place in operation the gas fired heating appliance on which the flue gas spillage sensor switch to be tested has been installed. Set the appliance thermostat for continuous operation. If other gas fired appliances are installed in the same building run those appliances at the same time.
  3. Allow the fans turned on in step 1 to operate for fifteen minutes.
  4. If the flue gas sensor spill switch trips during the fifteen minute test period this means that an unsafe condition exists. Check all of the appliances for a venting malfunction and check for adequate combustion air. (The occurrence of the flue gas spillage safety switch tripping may indicate inadequate combustion air but it could also indicate an unsafe chimney or some other unsafe condition.)
    Also see CHIMNEY INSPECTION DIAGNOSIS REPAIR.
  5. TURN OFF FUEL SUPPLY to the gas fired appliance that caused the safety switch to trip.
  6. DO NOT OPERATE THE GAS APPLIANCES UNTIL THE UNSAFE VENTING CONDITION HAS BEEN INVESTIGATED BY A PROFESSIONAL CONTRACTOR or GAS UTILITY COMPANY SERVICE PERSONNEL.
    See CARBON MONOXIDE WARNING.
  7. Return all windows, doors, fans, to their previous conditions of use.

SAFETY WARNING: If AT ANY TIME your gas fired equipment has shut down in SAFETY OFF position it may be due to a resettable flue gas spill sensor switch. Check with your heating service company - you might think you can avoid a costly heating service call, BUT BEWARE: because flue gas spillage is very dangerous, including the production of potentially fatal carbon monoxide gas, don't simply reset the system without finding out what caused the problem in the first place.

MORE SAFETY WARNINGS: in addition to our safety warning above, Tjernlund explains that flue gas safety switches are intended to alert the building occupants to a potentially dangerous condition.

But flue gas spillage safety switches are not a substitute for a regular chimney safety inspection nor do they replace regular heating appliance inspection and maintenance by a trained technician. Those steps must be taken as well.

What causes flue gas spillage:

Please see SPILL SWITCH, FLUE GAS DETECTOR for a discussion of the causes of flue gas spillage in buildings and for a description that contrasts inadequate combustion air with other causes of dangerous flue gas leakage into buildings.

Bachrach Corporation, a manufacturer of heating system test equipment opines that gas fired equipment is more likely to have flue gas spillage from a blocked chimney than from building depressurization due to inadequate combustion air supply. We're not sure what data supports that view.

Certainly home inspectors find many heating appliances installed in tiny closets with no outside combustion air and a door that, when shut, blocks off air to the appliance. We have also observed that gas fired heating equipment operated just fine in a building until a new owner installed a whole house ventilation fan system.

More examples of easy clues to unsafe or inadequate combustion air are given at COMBUSTION AIR DEFECT EFFECTS

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Continue reading at COMBUSTION AIR SAFETY in MOBILE HOMES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BACKDRAFTING HEATING EQUIPMENT

Or see CARBON MONOXIDE - CO and CARBON MONOXIDE WARNING

Or see COMBUSTION AIR for TIGHT BUILDINGS

Or see

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