Standby Generator Prep: A 7-Step Checklist Before the Next Outage

Who This Checklist Is For

You've got a Generac standby generator bolted to the side of your house — or you're one signature away from having one installed — and you actually want it to work when the grid drops. That's the audience here. Typical setup: a 20-26 kW unit, central AC, maybe a well pump, and a family that would rather not sweat through a July blackout on the third day of a heat advisory.

Here's the thing: most of the emergency service calls I get in the 48 hours after a big outage aren't the generator's fault. They're small failures that happened months earlier and nobody caught them. In my role coordinating residential installs and emergency callouts for a power contractor, I've handled 400+ installs over five years. The pattern doesn't change.

Seven steps. About 90 minutes of work on a Saturday. None of it needs a licensed electrician for the checking — some fixes do.

Step 1: Match the Generator to the Real Load — Not the Spec Sheet

Start with the number that actually matters: your AC's locked-rotor amps (LRA). A 26 kW Generac will handle a typical 4-ton central AC plus the fridge, well pump, and a handful of lights without breaking a sweat. A 16 kW won't — not if the AC kicks on at the same time as the compressor and the well pump.

Most buyers focus on the running wattage of their appliances and completely miss startup surge. Your 4-ton AC draws maybe 18 amps running, but 80+ amps on startup. That surge is what trips a generator into overload — and it happens in the first two seconds, before you understand why the lights flickered and went dark again.

What to actually do: find the data plate on your outdoor condenser, note the LRA, add 20% headroom. Compare that to the generator's surge rating, not its continuous rating. Most spec sheets bury the surge number near the bottom.

Step 2: Look at the AC Contactor Before You Trust It

This is the step almost nobody does, and it's the one that bites hardest. The contactor in your AC unit is a relay that closes a high-amperage circuit when your thermostat calls for cooling. Quick version of how a contactor works: a low-voltage signal from the thermostat energizes a coil, the coil pulls down a set of contacts, and 240V starts flowing to the compressor.

Those contacts pit and oxidize over time. Ants and spiders love nesting in the housing. When the contacts stick, your AC either won't start or won't stop. Neither is good in a blackout.

Cost check on how much is a contactor for an AC unit: for common residential sizes (1-pole, 24V coil, 30 or 40 amp), expect $15–$45 for the part. Add $80–$150 for a service call if you're not comfortable shutting off the disconnect and swapping it yourself. That's a $60 fix on a $12,000 generator install. Cheap insurance, and I've paid for worse.

What I actually check: pull the cover, look for pitting, arc marks, or melt marks on the contacts. If the plastic housing is discolored, replace it whether it's working or not. Contactor failure is on my top-three list of reasons AC systems go down during extended outages.

Step 3: Change the Air Filter — Yes, This Really Matters

A clogged filter forces the blower to work harder. Worse, restricted airflow drops the evaporator coil temperature and the unit starts icing up. Ice up plus sustained runtime on generator power is a recipe for compressor damage. I've seen it twice, and both times the owner had no idea their filter was three months past due.

If you're running a 16 x 20 air filter — one of the most common residential sizes in the US — buy a two-pack now and keep one in the garage. During storm season, the big-box stores sell out of the popular sizes within hours. Every spring, without fail.

Change it before the season starts and again at the midpoint. Stick with the MERV rating your system was designed for — going higher than spec chokes airflow and defeats the purpose.

Step 4: Test the Transfer Switch Under Load, Not at Idle

Your standby generator generac setup exists to flip on automatically. That flip is handled by the ATS — the automatic transfer switch. Testing it while nothing's running tells you almost nothing.

Here's what to do: turn on the HVAC, the fridge, the well pump if you have one, and a few lights. Then cut the main breaker to simulate an outage. Time how long until the generator picks up. A healthy system transfers within 10–15 seconds. If it takes longer, hesitates, or your lights flicker more than once, call service.

Something's weak. Battery, controller, or the transfer mechanism itself. Better to find out in April than at 2 a.m. in August.

Step 5: Verify Fuel Supply — Before the Storm, and Under Load

Natural gas and propane feed differently when the grid is stressed. Natural gas pressure drops upstream during regional outages because everyone's drawing at once. Propane runs out if your tank is sitting at 20%.

Check your line pressure or tank level before the season. If you're on propane, keep at least 40% in the tank going into storm season. A 22 kW unit burns roughly 3 to 3.5 gallons per hour under full load — that's about 48 gallons for a 14-hour outage. If your tank is a 250-gallon model, running it down to empty mid-storm is a much bigger problem than the money you saved by not topping off.

Step 6: Run a Partial-Load Test Before You Need It

Every year, end of April, I run a 30-minute test on my own setup. Here's the sequence, and this is what I recommend to anyone who wants to actually know their system works:

1. Kill the utility feed at the main breaker.
2. Let the generator transfer and stabilize for 2 minutes.
3. Turn on the AC. Wait 10 minutes.
4. Add the fridge, microwave, and a handful of lights.
5. Log the runtime and any flickers in your phone's notes app.

If the breaker trips or the unit shuts down mid-test, you just found your problem three months before you needed it to work. That's the whole point.

Step 7: Book Annual Service in Spring, Not Fall

Generac recommends annual maintenance. Most owners remember this when the first autumn storm hits the radar — which is exactly when every other owner is calling too.

Book in April or May. Technician availability is wide open. In October, you're looking at 2-3 week lead times in metro areas, and if a storm hits during that window, you're down. I've watched this happen to enough people that I stopped feeling surprised by it.

What annual service should cover: oil and filter, spark plugs, valve adjustment (yes, on air-cooled units), battery load test, and a full transfer switch inspection. If a quote is missing any of those line items, ask why. And this is where I'd start asking what's not included before what's the price. Per FTC advertising guidelines, claims need to be truthful and substantiated — in plain English, if a contractor won't itemize, that's worth a second look.

A Few Notes Before You Start

The whole list leans on one idea: catch small failures before they cascade. Here are the mistakes I see most.

• Skipping the contactor because it "looks fine." Pitting hides behind the cover. Have someone pull it.
• Trusting a ten-second transfer with nothing running. No load means no test.
• Topping off propane after the storm hits. By then, so is everyone else. Fill in March.
• Buying the filter the day of. Your size will be gone. Buy early.

My experience here is based on residential installs in a metro market — around 400 of them. If you're running a commercial standby system or an off-grid setup, the sequence looks different and the stakes are higher. I can't speak to those the same way.

Do the seven steps once. Storm season stops being a roll of the dice.