The Fall Furnace and Spring AC Checklists

The whole argument for seasonal HVAC prep fits in one sentence: it is better to find out in September.

Not because September is a lucky month. Because on the first genuinely cold morning of the year, every heating contractor within thirty miles receives the same phone call from several hundred people at once, and the person who tested their furnace six weeks earlier is not in that queue. Same thing in reverse on the first ninety degree afternoon.

The shoulder seasons are when a problem is an inconvenience. The first week of real weather is when the same problem is an emergency rate, a three day wait, and whatever part happens to be on the truck. Nothing about the repair changed. Only the timing did.

So here are the two checklists, split honestly into what you can do yourself and what genuinely needs somebody with instruments.

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The fall furnace checklist

Do this in September, or whenever you are still six weeks out from needing heat.

What you can do yourself

Run the heat, on purpose, for twenty minutes. This is the single most important item and the one everybody skips. Set the thermostat above room temperature and let the furnace complete a full cycle. You are confirming that it ignites, that the blower comes on, and that warm air reaches the registers. A furnace that will not light in September is a scheduled repair. The same furnace in January is a hotel room.

Expect a burning-dust smell on the first run of the season. It should fade within the first cycle or two. If it does not, that is worth a call.

Replace the filter, and write the size on your phone. Then set a recurring reminder. A restricted filter is the cheapest way to shorten the life of a blower motor.

Deal with the thermostat. Fresh batteries if it takes them, and switch the schedule over to heating mode rather than discovering in November that it is still running a summer program.

Clear three feet around the furnace. Storage creeps toward the mechanical room all summer. Combustion appliances need air and access, and a technician who cannot reach the panel is billing you to move your boxes.

Walk the registers and returns. Furniture moves over the summer. A blocked return is the most common self-inflicted airflow problem in a house.

Check the vent terminations outside. High-efficiency furnaces vent through PVC pipes out a side wall, and those pipes are at exactly the height where nests, leaves, and eventually snowdrifts live. Older furnaces vent up a flue, so look at the chimney cap. A blocked vent is a safety issue, not an efficiency issue.

Test every smoke and carbon monoxide detector, and read the date on the back. This gets its own section below because it is the item on this page with the highest stakes and the lowest cost.

If you have a whole-house humidifier, replace the pad, open the bypass damper for the season, and turn the water supply back on. If you have a condensing furnace, glance at the condensate line and make sure it drains freely.

What genuinely needs a technician

Do not attempt these. Several of them are the reason annual service exists.

• Heat exchanger inspection. A cracked heat exchanger is the failure that ends a furnace, and it is the reason this is a safety inspection rather than a tune-up. You cannot evaluate one by looking at the front of the unit.
• Combustion analysis and gas pressure. Instruments, not judgment.
• Draft and venting verification under actual operating conditions.
• Burner and flame sensor cleaning. A dirty flame sensor is one of the most common no-heat calls, and it is trivially cheap to prevent in the fall.
• Ignitor condition. Hot surface ignitors degrade before they fail, which a technician can see and you cannot.
• Safety controls: limit switches, rollout switches, pressure switches.
• Blower motor amp draw and wheel cleaning.
• Condensate trap and neutralizer on a high-efficiency unit.

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The spring AC checklist

Do this in April, before the first stretch of real heat.

What you can do yourself

Run the cooling for twenty minutes. Same logic, same reason, same month-of-relief. Set the thermostat below room temperature and confirm the outdoor unit starts, the air at the registers is genuinely cold, and nothing sounds new.

Replace the filter. Yes, again. This is a twice-a-year minimum and monthly-to-quarterly in a house with pets.

Uncover and clear the outdoor unit. Remove any winter cover completely. Give it about two feet of clearance on all sides, cut back the shrubs that grew into it last summer, and clear out the leaves that packed into the base over the winter. That unit rejects heat by pulling air across its coil, and everything crowding it makes the compressor work harder for the same result.

Rinse the condenser coil. With the power off at the disconnect, a garden hose on normal pressure, spraying from the inside out through the fins, removes a season of cottonwood and dust. No pressure washer. The fins bend if you look at them wrong.

Check the condensate drain. This is the item that protects your ceiling. The line that carries water away from the indoor coil clogs with algae, and when it does the pan overflows. Confirm it is draining, and clear it if it is not.

Look at the line insulation. The larger insulated refrigerant line running to the outdoor unit should still be covered. Sun and animals destroy that foam, and bare line is wasted capacity.

What genuinely needs a technician

• Refrigerant charge. Worth understanding: refrigerant is not consumed. It circulates in a sealed loop. If a system is low, it is low because it is leaking. "Topping it off" without finding the leak is not a repair, it is a subscription, and on an older R-22 system it is an expensive one.
• Capacitor testing. The start and run capacitor is among the most common AC failures, it is inexpensive, and it measurably weakens before it dies. This is the clearest example on this page of a part where inspection beats waiting.
• Contactor condition. Pitted contacts are visible to somebody who knows what they are looking at.
• Compressor amp draw and electrical connections.
• Evaporator coil and blower wheel cleaning, which is inside the ductwork.
• Metering device performance, superheat and subcool readings.
• Drain pan float switch test, which is the safety that prevents the overflow described above.

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Detectors get their own section

Every smoke and carbon monoxide detector in the house has a service life, and the sensors expire whether or not you keep changing the batteries.

• Test all of them with the button, and do it on the same weekend as the rest of this list.
• Read the date on the back. Manufacturers print either a manufacture date or a replace-by date. Carbon monoxide sensors typically last seven to ten years and smoke detectors around ten. A twelve year old detector with a fresh battery is a decoration.
• Placement matters more than count. Carbon monoxide detectors belong on every level and near sleeping areas.

This is a safety item, and it is separate from anything a service contract or an insurance policy does. It is also the cheapest line on the page.

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Keep the service record

Every item above gets more useful if you write down that you did it.

Start a note per system, or a folder, and log the date, who did the work, and what they found. Three groups of people will eventually ask you for that record: the next contractor who touches the system, a buyer's inspector when you sell, and anyone evaluating coverage on the house.

That last one is worth being direct about. Home service contracts cover mechanical failure from normal wear and use, and they generally exclude failures caused by lack of maintenance. A documented service history is the difference between a covered claim and an argument. It is also the difference between guessing at your system's condition and knowing it.

Two related distinctions that get muddled constantly in this category, stated plainly:

• Homeowners insurance covers sudden accidental damage. Fire, storm, theft, a sudden water discharge. A home service contract covers things wearing out from normal use. They solve different problems and neither replaces the other.
• Anything already broken is already outside both. Every legitimate service contract excludes pre-existing conditions and carries a waiting period, commonly around 30 days. Which is the real reason this article is about April and September rather than about January and July.

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The two-page calendar

	Fall, roughly September	Spring, roughly April
Run it	Full heating cycle, twenty minutes	Full cooling cycle, twenty minutes
Filter	Replace	Replace
Thermostat	Batteries, switch to heating schedule	Switch to cooling schedule
Outside	Clear vent terminations and chimney cap	Uncover unit, two feet clearance, rinse coil
Water	Condensate line on condensing furnace	Condensate line and pan, both
Safety	Test all detectors, check their dates	Confirm disconnect and line insulation
Technician	Heat exchanger, combustion, burners, safeties	Charge, capacitor, contactor, coil, amp draw

Two Saturdays a year, plus two service visits. That is the entire program, and it is most of the distance between the low end and the high end of every HVAC service life range published anywhere.

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What to do with this

Put both dates on a calendar right now, as recurring events, and attach this list to them. September and April, permanently. The value is not in reading the checklist. It is in the reminder arriving six weeks before you need the system, every year, without you having to remember.

And if you run through the fall list and everything works, that is exactly the right moment to know what coverage on those systems costs. A quote takes about 30 seconds, and it is a much easier question to answer in a warm house.