The Ultimate Guide on How to Fix a Gas Furnace

Learn How to Fix a Gas Furnace Like a Pro

Find out how to fix a gas furnace like you were born to do just that. This guide covers all the essentials and will answer all your furnace questions to leave you no room for doubts or second-guessing.

1. How to turn on a gas furnace?

  • Look for your furnace’s breaker. It is a part of your electrical panel that can often be found in the garage, basement, or utility room. The breaker should have a label of a gas furnace sticker. Turn it on.
  • Look for the switch and turn it on. You can find it below your basement stairs, in the ceiling, or in the room with the furnace and often at eye level or perhaps a bit higher.
  • Set the thermostat. Check if the furnace is on and make sure that you have set the selector switch to “heat.” Then, make adjustments to your set temperature.

2. How to inspect and replace your furnace filter?

  • Regular inspection and replacement of your furnace filter especially during the winter season. Replacement is often done every three to six months.
  • Start by carefully opening the panel door or external rack of the furnace.
  • Slide the furnace filter to take it off. Check the filter for signs of darkness or discoloration.
  • If it’s no longer possible to see through the filter, a replacement is absolutely necessary.
  • Slide your new furnace filter into the furnace all the while making sure you install it in the airflow’s direction.

3. How to check for your furnace’s airflow?

  • Do the garbage bag airflow test to determine the volume of airflow coming from your furnace registers. It’s a quick way to find out the length of time it takes to fill an ordinary plastic bag and estimate airflow.
  • To do this test:
    • Put a tape in the mouth of the garbage bag to a piece of cardboard or coat hanger to make sure it stays open.
    • Flatten the bag and put it over the exhaust hood or register.
    • Count how long it takes (number of seconds) it takes for the bag to be fully inflated.
    • Inflation time:
      • 2 seconds = 37 L/s (75 cfm)
      • 4 seconds = 20 L/s (40 cfm)
      • 10 seconds = 10 L/s (20 cfm)
    • For measured airflow lower than 10 L/s = only a small amount of heat is being delivered into the room. It needs to be checked to find out why only a small amount of heat passes through.
    • You can also do the garbage bag test if you replaced your HVAC system recently or underwent major home renovations.

4. For a gas furnace that does not ignite:

  • An ignition failure is a possible cause if your furnace is on and the fan is likewise running but all you get from it is cold air.
  • Turn the switch off for at least ten seconds and then turn it on once more to reset the furnace.
  • If the problem persists, contact your furnace technician.

5. Ultimate Checklist Guide on How to Fix a Gas Furnace

Check the following things first before calling a furnace technician in case your furnace starts acting up:

  • Is the furnace on?
  • Is the thermostat set on “heat” mode and the temperature on normal heat settings?
  • Is there an ice or snow buildup blocking the furnace’s vents?
  • Are there fresh batteries powering the thermostat?
  • Is the circuit breaker positioned properly in the electric panel?
  • Is the door to the furnace properly closed?
  • Did you replace the filter recently?

Once you finish checking this checklist and your central furnace is still no good, call your local furnace contractor to fix the problem for you.

6. How to get rid of clogs on vents properly?

For issues concerning the exterior vent, inspect it briefly to check for signs of ice or snow buildup or any item that is possibly blocking the vent. If there is, turn off your furnace’s power before getting rid of the obstruction. Get rid of the clog and turn the furnace back on as soon as you’re done.

7. How to prevent air leaks and heat loss?

  • Seal off leaks around doors and windows:
    • Get rid of the trims carefully.
    • Use oakum, foam backer rod, or an expanding polyurethane foam to seal big gaps or cracks.
    • Replace the caulk and trims along the edges.
  • Seal off leaks along the baseboards:
    • No need to take off the baseboard, just caulk along the seams.
    • Caulk between the floor and the wall by first taking off the baseboard.
  • Seal off leaks surrounding electrical outlets on exterior walls:
    • Turn off the power and take off the cover of the outlet.
    • Put a foam insulating pad.
    • Change the outlet cover and turn the outlet’s power back on.
  • Seal off leaks in an unfinished basement.
    • Caulk below the basement sill plate and all over the joists using an acoustical sealant or rubber-based caulking.
    • Caulk all cracks and gaps where the ductwork enters a ceiling or wall.
    • Use a duct-taped insulation batt or preformed wraps to insulate the ductwork.
  • Seal off leaks in the attic:
    • Seal all cracks.
    • Close the door tightly after weather stripping your attic door.

8. How to act once you detect gas smell lingering in your home?

You likely have a gas leak at home once you smell a rotten egg scent. Open all your windows but do not turn on any electrical switches. Go to your neighbor and call your furnace contractor and local utility company right away to report the incident.

After going through this checklist, you will no longer be clueless as to how to fix a gas furnace by yourself once you experience any of these issues at home.