Fall in the San Gabriel Valley and the San Fernando Valley is not a season so much as a handoff. The AC is still running in October, the first Santa Ana wind arrives with dust and fire smoke, and then one night in November the house is 58°F at 6am and the furnace has to work for the first time since March. The checklist below is built around that sequence. Do the AC items first, the air-quality items when the wind forecast turns, and the heating items before you need them.
Late September and October: the AC is not done yet
The cooling season here runs into October, and the outdoor unit has been working since May.
- Change the filter. It has been catching five months of summer dust. A dirty filter going into a smoke event is the worst timing there is.
- Clear the outdoor unit. Pull leaves and debris off the top grille and out from around the base. Keep two feet clear on all sides. Do not cover it yet; it may run again on a 95°F Halloween.
- Rinse the coil. With the power off at the disconnect, a gentle hose rinse from the outside of the condenser coil knocks off the summer's dust. Chemical cleaning is a tech job.
- Check the condensate drain. A drain that has been dripping all summer sometimes clogs with algae right at the end of the season. Look at the pan under the indoor coil if you can see it. Standing water means the line is slow.
- Note anything that changed. A room that fell behind, a new noise, a breaker trip on a hot day. Those get looked at during the fall visit.
When the Santa Ana forecast turns: air quality
Santa Ana winds bring dry air, dust, and in a bad year, wildfire smoke that can sit over the basin for days. Your HVAC is the one air filter that covers the whole house.
- Have a spare filter in the closet. During a smoke event you may need to change it after a week, not a month.
- Know your system's filter rating limit. A MERV 13 filter catches fine smoke particles, but not every blower can pull air through one. If the return starts whistling after a filter change, the filter is too restrictive for the system.
- Set the fan to ON during a smoke day. Running the blower continuously keeps air moving through the filter even when there is no call for cooling or heat.
- Close the fresh-air intake if your system has one. Most residential systems here do not, but some newer installs and most rooftop package units do. A tech can show you where it is.
- Set the thermostat and leave the windows shut. The house stays cleaner that way.
November: heat for the first time
The first cold night is when heating problems announce themselves, and it is when every contractor's phone rings at once. Test the system before then.
- Run the heat for 15 minutes on a mild afternoon. Set the thermostat 5 degrees above the room temperature and let it run. You are checking that it lights, that warm air arrives at the registers, and that it shuts off when it should.
- Expect a dust smell the first time. Dust settles on the heat exchanger and the burners over summer and burns off the first time the heat runs. It should clear within a few hours. A smell that lasts, a smell like something electrical, or any smell of gas is a stop-and-call.
- Replace the thermostat batteries if yours takes them. A thermostat that dies in December leaves you with no heat and a blank screen.
- Check every register and return. Rugs and furniture block registers. Heat needs the same airflow cooling does.
- Test the carbon monoxide detector. Push the button. If it is more than a few years old, check the date on the back; they have a service life.
- If you have a wall furnace, vacuum the front grille and the area behind it. Lint and pet hair collect there over summer, and it is the first thing that burns when the unit lights.
- If you have a floor furnace, make sure nothing is on or near the grate. The grate gets hot enough to scorch a rug and hot enough to hurt a child or a pet. These are common in the 1920s bungalows across Pasadena, CA, Altadena, and South Pasadena, and most have never had a safety check.
What you can check yourself
Everything in the lists above is a homeowner task. To put it in one place:
- Change the filter, and buy a spare.
- Clear and rinse the outdoor unit with the power off at the disconnect.
- Look at the drain pan.
- Run the heat once before you need it, and note the smell.
- Swap thermostat batteries.
- Unblock registers and returns.
- Test the CO detector.
- Vacuum the wall furnace grille; clear the floor furnace grate.
Leave the furnace cabinet closed. Do not adjust the gas valve, relight a pilot that keeps going out, or touch the flue pipe connections. Those are the items on the tech's list.
When to call a licensed tech
Book a fall visit if the furnace has not been inspected in the last year, if it is an older gas furnace or any wall or floor furnace, if the heat test produced a lasting smell or did not light, or if the AC gave you trouble over summer. A furnace maintenance visit checks the things you cannot see: the heat exchanger for cracks, the flue for proper draft, the gas pressure, the flame sensor, the ignitor, and the safety switches. Cracked heat exchangers are the reason carbon monoxide detectors exist, and they do not show from the outside.
If you want the AC side done in the same trip, HVAC maintenance covers both, including the coil, the capacitor, the refrigerant charge, and the electrical connections. Older homes with a wall or floor furnace should ask for a tech who does wall and floor furnace repair specifically. Those units have their own parts and their own failure points, and not every tech works on them.
Two things that come up every fall and are not HVAC: the chimney and fireplace are a separate trade, and so is the attic insulation. We will point out what we see, but we do not do that work.
Common questions
When should I do the fall check?
October. The AC is winding down, the furnace has not been asked to do anything yet, and the calendar is open. By the second week of November, everybody with no heat is calling at once.
Do I need a fall visit every year?
For a gas furnace, a yearly inspection is what the manufacturers and the trade recommend, mainly for the heat exchanger and flue check. For a heat pump, one visit a year covers it in most homes. A wall or floor furnace that has gone years without a look should not go another year.
The furnace runs fine. Why inspect it?
Because the failure that matters, a cracked heat exchanger, does not stop the furnace from running. It runs fine and leaks combustion gases into the supply air. The inspection is for the thing that has no symptom.
If you want the fall check done properly, book a $69 diagnostic. We tell you the fee before booking and credit it toward the work. Call Boost Services Heating and Cooling at 818-277-5056 or send us a message and we will usually get to you within a few hours.
Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.