HVAC maintenance: what to do and when

The intervals, in one place

Filters, the one that isn't optional

A filter is there to keep the equipment clean first and the air clean second. When it loads up, airflow drops, the system runs longer for the same result, and in cooling weather the coil can get cold enough to ice over.

Every one to three months is the range, and the spread is real: filter thickness, pets and how hard the system is running move it more than the calendar does. The practical version is to look monthly and change when it's gray. The filter question has its own page, including why a finer filter isn't automatically a better one.

The annual service, and when to book it

Once a year, and the month you choose matters more than most people expect.

Spring for the cooling side, fall for the heating side. Booking in the shoulder season means shorter waits, more flexible appointments and often better pricing, because you aren't competing with everyone whose system just failed on the first hot or cold day of the year. A technician can also tell you what your particular system wants and how often. No general schedule can do that part.

Airflow around the house

Plenty of comfort complaints have nothing to do with the equipment. They're in the rooms: a blocked register, a closed damper, a door that stays shut.

• Vents and registers, every three months. Vacuum the supply and return grilles and check nothing is blocking them. A sofa moved eighteen inches over a return is a surprisingly common cause of one cold room.
• Ceiling fan direction, twice a year. Counterclockwise for summer, clockwise for winter.
• If it's a heat pump, check the backup heat before the first cold snap. A heat pump leans on electric or gas backup when the outdoor temperature drops far enough, and that backup can sit unused for eleven months. A system that heats fine in November and struggles in January is often a backup that never came on.
• The condensate drain, through cooling season. Air conditioning pulls water out of the air and sends it down a narrow pipe, and that pipe grows algae. The signs are standing water in the drain pan, a damp patch near the indoor unit, or a system that shuts itself off on a hot day because a float switch has tripped. Many systems also have a secondary overflow pan under the unit, and anything sitting in it is telling you the primary drain has already failed.
• Balance, not brute force. Closing vents in unused rooms to push more air elsewhere raises pressure in the ductwork rather than helping, and a system fighting its own ducts isn't saving anything. It's worse on a modern variable speed blower, which responds to the resistance by working harder rather than by giving up.

The ducts that aren't part of the system

Three ducts in a typical house move air and have nothing to do with the heating and cooling equipment. They get forgotten precisely because they aren't part of anything.

• The dryer vent, yearly. Lint in a duct next to a heat source is the highest consequence item on this page. Slow drying is the first sign, and the dryer vent has its own page.
• The bathroom exhaust fans, twice a year. Vacuum the grille and the blades. A fan that no longer pulls is no longer removing shower moisture, and weak fans invite mold.
• The range hood filters, monthly. Grease clogged filters push smoke back into the kitchen. Mesh filters usually wash; charcoal ones are replaced.

Reading the symptoms

What needs a technician instead

Filter changes, grille vacuuming and fan direction are homeowner jobs by design: no tools, no panels, nothing behind a cover.

Anything past the filter slot is not. A residential system carries line voltage and refrigerant under pressure, and in most houses a gas burner and a flue as well, and diagnosing it takes gauges and meters. What's genuinely useful from your side is noticing a change early and being able to describe it: what the noise is, when it started, which rooms are affected.

Patina keeps each of these on its own interval, the annual service included, and reminds you in the shoulder season rather than the week you need it.