You can safely clean the parts of a furnace you can reach without opening the burner compartment: the air filter, the cabinet and the floor around it, the registers and return grilles, the condensate drain on a high-efficiency furnace, and the vent pipes outside. This guide from Alpha Mechanical, the family-owned heating and cooling company based in Fair Oaks, covers the homeowner jobs that keep a furnace breathing and marks where the technician's work begins.
Key Takeaways
- Eight homeowner-safe steps: power off, filter, cabinet, registers and returns, condensate drain, vent pipes, carbon monoxide alarms and flame color, then one full heating cycle.
- Leave the burners, flame sensor, igniter, blower, inducer, heat exchanger, gas valve and wiring to a technician. Those parts involve gas, carbon monoxide and line voltage.
- A steady blue flame is normal. A yellow or orange flame means the burner needs a technician.
- Do this once a year before the heating season; October and November are the usual window in Sacramento. Our furnace tune-up is a flat $99 for the technician's half of the job.
What can a homeowner safely clean on a furnace?
A homeowner can safely change the filter, dust the outside of the cabinet, vacuum the registers and return grilles, keep the floor around the unit clear, check the condensate drain and the vent pipes, and test the carbon monoxide alarms. None of that needs a tool that opens the furnace. The line is the burner compartment panel. The one door a homeowner opens is the blower door, and only when the filter sits behind it and the power is off.
Here is how the job splits:
| You can do it | Leave it to a technician |
|---|---|
| Replace the air filter | Clean the burners and flame sensor |
| Dust the cabinet and clear the area around it | Clean or service the blower wheel and motor |
| Vacuum registers and return grilles | Test the igniter and inducer motor |
| Look at the condensate drain hose and pan | Clear or rebuild the condensate trap |
| Look at the vent pipes outside | Inspect the heat exchanger for cracks |
| Test the carbon monoxide alarms | Measure gas pressure and test for carbon monoxide |
| Look at the flame through the viewing window | Tighten wiring and measure motor amperage |
Each item in the right column sits next to gas, combustion gases or line voltage, and two of them, a cracked heat exchanger and a carbon monoxide leak, cannot be seen without instruments.
What do you need before you start?
You need a flashlight, a vacuum with a brush attachment, a damp cloth, and a replacement filter of the right size. The size is printed on the frame of the filter you have now, for example 20x30x1, like the filter in the step 2 photo. You do not need a screwdriver or a nut driver: if a step seems to need one, it is a technician's step.
If your furnace is in the attic, go up only if there is a solid walkway to the unit and good light, and step only on the walkway or the framing, never on the ceiling drywall between joists. If there is no safe path to the furnace, leave the attic checks to a technician.
If you are not sure where your filter sits, our guide to where the HVAC filter is located covers the common spots in Sacramento homes: a return grille in a hallway or ceiling, a slot beside the furnace, or a rack inside the blower compartment door.
How do you clean a furnace safely? 8 steps
Work through these in order, with the furnace off until step 8.
Step 1: Turn the thermostat off and switch off the furnace
Set the thermostat to off, then switch off the furnace's power. Most furnaces have a service switch that looks like a light switch on or near the unit; some attic and closet furnaces run on a power cord plugged into a nearby outlet, like the cord in the photo at the top of this guide. Do not touch the gas valve or the gas line. Turning the power off is enough for every step below.
Step 2: Replace the air filter
A clogged filter is a common reason a furnace overheats, cycles on and off or blows weak air, and it is the one part you are meant to change yourself. Slide the old filter out, note the airflow arrow printed on the frame, and put the new one in with the arrow pointing toward the furnace.
Check the filter more often during a smoky fall: wildfire smoke loads a filter faster, and our wildfire smoke guide explains what to watch. If your filter sits behind the blower compartment door, the power must already be off from step 1. That door holds a safety switch that stops the furnace when the door is open, so seat it fully when you put it back; our guide to the furnace safety switch explains why a loose door keeps the furnace from starting. Open only that door, and with it off, touch only the filter: leave the blower, the wiring and the control board alone. Never remove the upper burner panel.
Step 3: Dust the cabinet and clear the area around it
Wipe the outside of the cabinet with a damp cloth and vacuum the floor around the furnace. Then clear the space: furnaces in Sacramento garages and closets can share room with storage. Move boxes, laundry, paint and anything flammable away from the unit so the burners get combustion air and nothing sits near the heat.
Step 4: Vacuum the registers and return grilles
Vacuum the supply registers in each room and the return grilles with the brush attachment. Open any registers that were closed for summer, and pull furniture and rugs away from returns. A furnace can only heat the house with the air it can draw in, so a blocked return makes it work harder for less heat.
Step 5: Check the condensate drain on a high-efficiency furnace
A high-efficiency furnace, the kind with white plastic vent pipes, makes water as it runs and drains it through a hose or pipe. Look for water on the floor, a full drain pan, or a kinked or disconnected hose. Do not take the trap apart. On many systems, a float switch stops the system on purpose when the drain backs up; our guide to the condensate safety switch explains how that switch works and why it is never bypassed.
Step 6: Look at the vent pipes outside
Find where the furnace vents: white plastic pipes through a wall or the roof on a high-efficiency furnace, or a metal flue on an older one. From the ground or the garage, look for leaves, nests or anything blocking a pipe end, and for metal flue sections that have come apart. Pull leaves or debris away from the outside of a pipe end you can reach from the ground, but do not reach into the pipe: anything inside it, a nest included, is a technician call. A disconnected or damaged flue is a call to a technician, not a repair to attempt.
Step 7: Test the carbon monoxide alarms and plan the flame check
Press the test button on each carbon monoxide alarm and replace any that fail. Then plan to look at the flame in step 8. Many furnaces have a small viewing window in the burner door, so you can see the flame without opening anything.
A properly adjusted burner produces "a steady blue flame with very small amounts of yellow or orange," and if the flame is yellow or orange, the instruction is to call a licensed repair service to have the equipment adjusted (Lawrenceburg Utility Systems, Natural Gas Safety). Never remove the burner door to get a better look.
Step 8: Restore power and watch one full heating cycle
Switch the furnace back on and set the thermostat to heat a few degrees above room temperature. On most modern furnaces, a normal start runs in order: the draft fan, the igniter, the burners, then the blower a little later. Look at the flame through the viewing window if your furnace has one, and let the furnace run until the thermostat is satisfied.
A light dusty smell on the first run of the season is normal and fades; our guide to a furnace burning smell explains which smells are not. Stop and call if the furnace does not start, starts and shuts off within a few minutes again and again (see furnace short cycling), or the flame looks yellow, orange or ragged.
What should you leave to a technician?
Leave everything behind the burner panel, and everything in the blower compartment except the filter, to a licensed technician: the burners, flame sensor, igniter, blower wheel and motor, inducer motor, heat exchanger, gas valve and the wiring. Those parts involve gas, carbon monoxide and line voltage, and the most serious fault, a cracked heat exchanger, is found with instruments rather than by eye.
That is the half of furnace cleaning our heating tune-up covers. The Alpha Mechanical furnace tune-up is a flat $99 and follows a 15-point checklist that includes a carbon monoxide test, cleaning the flame sensor, testing ignition, inspecting the heat exchanger, measuring gas pressure and checking the electrical connections and blower. If you want to know what a crack looks like and why it matters, read our guide to cracked heat exchanger symptoms.
When should you clean your furnace in Sacramento?
Clean the homeowner parts once a year before the heating season, and change the filter whenever it looks loaded. In Sacramento, October and November are the usual window: the furnace has sat unused through the summer, and anything you find gets fixed before the first cold night rather than during it.
A technician visit fits the same window. If your furnace runs through a smoky fall or you have pets, check the filter every month through the winter.
What if you smell gas or a carbon monoxide alarm goes off?
Stop, leave the house and get everyone out. PG&E's instruction for a suspected leak is to leave the area immediately, avoid anything that could spark, including light switches and phones, until you are a safe distance away, and then "call 9-1-1 for emergency assistance and then call PG&E at 1-800-743-5000" (PG&E, Gas Safety). Do not go back in to switch the furnace off.
For a carbon monoxide alarm, PG&E's guidance is to "get out of the building and make sure that no one goes back into the building until you are assured that it is safe," to "call 9-1-1 and seek medical attention if anyone experiences possible carbon monoxide poisoning symptoms," and not to use the appliance again "until it has been determined to be safe by a qualified professional" (PG&E, Carbon Monoxide). Leave the furnace off until a technician has checked it.
Get the technician's half done
Alpha Mechanical is a family-owned company based in Fair Oaks. We service furnaces across the Sacramento area, including our home base of Fair Oaks and neighboring Carmichael. Book a furnace tune-up, or call 916-848-5980.