What to Keep on Hand: A Short Homeowner HVAC Supply List
Four inexpensive things in a closet prevent a surprising number of problems and make emergencies less bad.
Homeowners should keep spare air filters in the correct sizes, distilled white vinegar for condensate drain maintenance, a probe thermometer for measuring temperature split, and a basic flashlight and screwdriver set. Together these cost very little and prevent or diagnose most common HVAC problems.
The list
- Spare filters, correct sizes, at least two of each. Buy a year at a time. The filter you do not have is the one you do not change.
- Distilled white vinegar. One bottle lasts a season of monthly condensate drain flushes.
- A probe thermometer. Inexpensive, and it lets you measure temperature split — the single most useful performance number a homeowner can take.
- A flashlight and a basic screwdriver set. For finding the filter, the disconnect, and the drain access at 9pm.
- A roll of painter's tape and a marker. For writing readings and dates inside the air handler door.
- Optional: a wet/dry vacuum. Clears a clogged condensate drain from the outdoor termination, which resolves a common shutdown.
Filters deserve the most attention
Buy a year's supply at once. It is cheaper per filter, and more importantly it removes the friction that causes filters to go unchanged for four months.
Note every size. Many Valley homes have two return grilles, or a filter at the return and another at the air handler, and homeowners regularly change one for years without discovering the other.
Write the size on the air handler door with tape and a marker. In five years when someone else is standing there wondering, they will find it.
And set a phone reminder every 30 days during cooling season. The calendar will not remind you and the filter will not look that bad until it is well past due.
Why the thermometer matters
Temperature split — the difference between return air and supply air — is the closest thing a homeowner has to a performance measurement.
Run the system fifteen minutes, measure at the return grille, measure at a nearby supply register, subtract. Should be 16 to 22 degrees. Below 14 suggests low refrigerant or a weak compressor; above 24 suggests restricted airflow.
Take it every spring and write it down with the date and the outdoor temperature. Three years of readings turns "it does not seem as cold as it used to" into a documented trend, which is exactly what a technician can act on.
What not to keep
Refrigerant cans. DIY refrigerant is a bad idea. Charging by pressure alone without measuring superheat or subcooling typically results in an incorrect charge, and an overcharged system damages the compressor. It is also regulated.
Leak sealant. It can clog metering devices and contaminate recovery equipment, which means many companies will refuse to service a system that has had it added.
Spare capacitors. They hold a dangerous charge, they need to match the equipment, and replacing one without checking why it failed accomplishes little.
Coil cleaner from the hardware store, unless you know it matches your coil material. The wrong chemistry damages coils.
The information worth writing down
- Filter sizes and locations, all of them
- Outdoor unit model and serial number, and its manufacture date
- Indoor unit model and serial number
- Refrigerant type
- Installation date and contractor
- Warranty expiration and registration status
- Annual temperature split readings with dates and outdoor temperatures
- Your HVAC company's phone number
One sheet of paper inside the air handler door covers all of it. It is the cheapest thing on this list and the one most likely to matter in five years.
The wet/dry vacuum trick
Worth knowing because it resolves one of the most common summer shutdowns.
When a condensate drain clogs, the float switch shuts the system down. Find the drain termination outside — usually a PVC stub near the foundation or an exterior wall — hold a wet/dry vacuum hose over it, seal around it with a rag or your hand, and run the vacuum for a minute or two.
It frequently pulls the blockage straight out. Follow up with vinegar in the access tee to disrupt what caused it. If water is already in the ceiling, stop and call instead.
Frequently asked
What HVAC supplies should a homeowner keep?
Spare filters in every size your home uses, distilled white vinegar for monthly condensate drain flushing, a probe thermometer for measuring temperature split, and a flashlight and screwdriver set. All inexpensive, all useful.
Can I add refrigerant to my A/C myself?
We strongly advise against it. Charging by pressure alone without measuring superheat or subcooling usually results in an incorrect charge, and an overcharge damages the compressor. A system that is low also has a leak, which the refrigerant does not address.
How do I unclog an A/C condensate drain?
Hold a wet/dry vacuum hose over the outdoor drain termination, seal around it, and run it for a minute or two — it often pulls the blockage straight out. Follow with a cup of distilled white vinegar in the indoor access tee. If water is already in the ceiling, call instead.