Gas furnace inspection checklist: I forget anything?


Check the following:

  1. Adequate combustion air

  2. Gas supply for:
    a. Shut off near the furnace
    b. Sediment trap/drip leg
    c. Proper gas supply piping
    Acceptable materials are black steel, corrugated stainless steel tubing CSST, and copper, although permissible copper varies by jurisdiction and may be limited to certain types.

    d. Flex connector
    Flex connectors are maximum 3 feet for furnaces and must have a shutoff where it connects to rigid gas piping. Flex connectors cannot pass through walls, floor, or ceilings, and cannot be concealed. Flex connectors may be required in areas subject to earthquakes.

  3. Combustion exhaust venting
    a. Vent material (plastic means high efficiency)
    b. Vent connector proper slope (1/4” per foot)
    c. If the furnace and a water heater connect to the same vent, the water heater should connect upstream from the furnace.
    d. If the furnace and a water heater connect to a chimney, the water heater should connect above the furnace, and a cleanout should be installed within 6” below the furnace vent connector.

  4. Presence of a kill switch.

  5. Presence of a humidifier

  6. Ducts
    a. Type?
    b. Sealed?
    c. Insulated?
    d. Securely attached

  7. Note the filter type (electronic/fabric), location and condition

  8. Shut off the furnace at the kill switch

  9. Remove the access covers

  10. Note dirt, debris, and corrosion
    11 Photograph the manufacturer’s label/ data plate

  11. Examine the burn chamber
    a. Scorching
    b. Corrosion
    c. White residue
    d. Loose or damaged burners

  12. Examine the blower compartment
    a. Dirty or greasy buildup on the blower vanes

  13. For high efficiency furnaces, check for proper condensate discharge.
    a. Corrosion resistant piping (ABS, PVC, CPVC, copper, (not coiled tubing) PEX, polyethylene, polypropylene).
    b. ¾” minimum
    c. Condensate pumps appear to be in satisfactory condition with proper electrical connections (not extension cord)
    d. Trap are installed in condensate lines as required by the manufacturer.
    e. Horizontal runs must slope minimum 1/8 inch per foot
    f. Condensate must discharge to an approved location. Not a street, alley, or sidewalk. Check locally for “approved locations”. Most discharge to floor drains. Furnaces in attics must have a drip pan with overflow and condensate discharge to an approved location.

  14. Turn the thermostat up high

  15. Turn the furnace on at the kill switch

  16. Watch for proper operation. You may need to depress the access cover safety switch for the furnace to operate.
    a. The burners will ignite and run for a short time before the blower activates. Watch for any change in the flame when the blower activates. Changes in the flame can indicate a cracked heat exchanger. Recommend service. Flame color should be blue. Yellow or white flame indicates a need for service.
    b. Listen to the blower. Any unusual noise indicates a need for service.

  17. Check temperatures at registers with a digital thermometer. Comment on any that are significantly hotter or colder than the rest.


I added a couple in red:D:D

Thanks Charlie!

Galvanized is acceptable for gas in some AHJ

Copper and galvanize is not allowed in Okla for gas. Galvanize can be mistaken for a domestic water line and is considered as a safety issue in most areas that I am aware of. Not saying your wrong just saying its not a good idea.

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In Illinois copper lines must be soldered, flare and compression connectors are not allowed, per Ill plumbing code. Know your area.

According to the National Electrical Code, a gas furnace (or any other central heating equipment) must be on its own circuit. So connecting a water heater (or anything else), would be a code violation.

National Electrical Code 2014

Chapter 4 Equipment for General Use

Article 422 Appliances

422.12 Central Heating Equipment. Central heating equipment other than fixed electric space-heating equipment shall be supplied by an individual branch circuit.

Exception No. 1: Auxiliary equipment, such as a pump, valve, humidifier, or electrostatic air cleaner directly associated with the heating equipment, shall be permitted to be connected to the same branch circuit.

Exception No. 2: Permanently connected air-conditioning equipment shall be permitted to be connected to the same branch circuit.

Chapter 1 General

Article 100 Definitions

Branch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

Since we’re getting away from the furnace a little and discussing plumbing/fuel supply, the presence of CSST and bonding is important.
Several posts about it, just thought it should be mentioned.


Gas furnace doesn’t have a “kill” switch" it has a service disconnect.
The gas valve needs to be within 6 feet of the appliance.
Don’t need to use the service disconnect to remove the cover, you will want to see the blower disconnect function when you remove the blower door (if you do).
The only reason to open the upper cover (burner cover) is to copy serial number.

CSST should not enter cabinet on furnaces with a metal roof flue. IAPMO ANSI LC 1 ● CSA 6.26

Watch the burner operation cycle; draft inducer, igniter glows, gas comes on lites.

Observe proper flame sensor location (if out of place or dirty gas will shut off).

Thanks for sharing this gas furnace inspection checklist! I had one installed by Clover Services about two years ago and it might probably be a good idea to do a thorough inspection soon just to be sure that there are no issues that need to be fixed. I’ll be using this as some sort of checklist, thanks again!

Service disconnect (aka “kill switch”) is only needed if the appliance is not within line of sight of the panel. In Oregon a lot of furnaces are in the garages along with electric panels so a separate disconnect isn’t needed.

On the list I don’t see front service clearance but may have missed it.