How to Size a Generac Generator in Fort Pierce, FL
Sizing a Generac generator starts with a list, not a house size: which circuits you want powered during an outage, what each one draws while running, and what the largest motors draw when they start. This guide walks through that list and explains why the air conditioner decides the size.
Sizing a Generac generator starts with a list, not a house size: which circuits you want powered during an outage, what each one draws while running, and what the largest motors draw when they start. This guide walks through that list, explains running versus starting watts, and shows why the air conditioner usually decides the size.
Step 1: decide what gets backed up
The first decision is the biggest one. Essential-circuit backup covers what matters most during an outage: refrigerator, lights, fans, internet equipment, a few outlets, and sometimes one air conditioner. Whole-home backup covers everything as normal, including all air conditioning, laundry, and kitchen loads. Whole-home backup needs a substantially larger generator and fuel supply, so most homes start with essential circuits and add the air conditioner as a separate decision.
| Choice | What it powers | Generator size | Best for |
|---|---|---|---|
| Essential circuits | Refrigerator, lights, fans, internet, selected outlets | Smaller | Most homes, lower cost |
| Essential circuits plus AC | Above, plus one air conditioner | Medium — AC starting watts decide | Homes that need cooling in an outage |
| Whole home | Everything as normal | Largest | Homes that want no change during an outage |
Step 2: add running watts, then starting watts
Running watts are what each appliance uses while it runs. Starting watts are the surge a motor draws for a moment when it starts, often two to three times its running watts. Air conditioners, well pumps, and refrigerators all have starting surges, and the largest one usually sets the generator size. A generator sized only on running watts will stall or trip when the largest motor starts, so starting watts must be in the calculation.
- List every circuit you want backed up, with its appliance.
- Note running watts for each, from the appliance label or manual.
- Note starting watts for each motor load, especially air conditioning.
- Add running watts together, then check the largest starting surge on top.
Why the air conditioner usually decides the size
Central air conditioning is the largest motor load in most Fort Pierce homes. Its starting watts alone can exceed the running watts of every other essential circuit combined. That is why the air conditioner question — on backup power or not — swings generator size more than any other choice. If the answer is yes, the generator must be sized to start it. If the answer is no, a much smaller generator can cover the rest of the home, and portable fans and a smaller backup plan may be enough.
How generator sizing works
Fuel, transfer switch, and placement
Fuel, transfer switch, and placement are part of sizing, not afterthoughts. Fuel type depends on what is available at the home, and propane tank size or gas line capacity can limit what a generator can run and for how long. The automatic transfer switch must be sized for the circuits it backs up, and it is what makes standby power automatic. Placement affects noise, access for service, and clearance from the home — a provider should confirm all three during the site assessment, not after the generator is ordered.
Common sizing mistakes
- Sizing from house size or square footage alone, without a circuit list.
- Counting running watts only and forgetting starting watts.
- Adding every circuit to backup power, then being surprised by the generator size and cost.
- Forgetting fuel: a generator that cannot run long enough for a real outage is undersized in practice, whatever its watt rating.
- Skipping the panel check: a generator installation may need panel or transfer switch work that sizing alone does not show.
Essential circuits versus whole-home backup at a glance
What changes the cost
No single price is published here, because generator cost depends on size, fuel setup, transfer switch, panel work, placement, and permit and inspection coordination. A smaller essential-circuit system and a whole-home system are different jobs with different scope. A provider should price your specific circuit list, fuel setup, and panel after a site assessment, not from house size alone.
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Frequently asked questions
What size Generac generator do I need for my home?
It depends on what you want powered during an outage: a few essential circuits, or the whole home. Essential-circuit backup needs a smaller generator than whole-home backup, and the difference is large. The right size comes from listing the circuits you want backed up, adding their running watts, and adding the starting watts of the largest motors, usually air conditioning. A provider should size from your actual list, not from house size alone.
What is the difference between running watts and starting watts?
Running watts are what an appliance uses while it runs. Starting watts are the higher surge it draws for a moment when its motor starts — often two to three times its running watts for air conditioners, well pumps, and refrigerators. Starting watts matter most for sizing, because a generator that can run your loads but cannot start your air conditioner will stall or trip when the air conditioner kicks in.
Should I back up essential circuits or the whole home?
Essential-circuit backup powers what matters most — refrigerator, lights, fans, internet, a few outlets, and sometimes one air conditioner — and needs a smaller generator and a smaller fuel supply. Whole-home backup powers everything as normal and needs a larger generator, a larger fuel supply, and a higher cost. Most homes choose essential circuits, with the air conditioner as the decision that swings the size most.
Does my air conditioner decide the generator size?
Usually, yes. Central air conditioning is the largest single motor load in most Fort Pierce homes, and its starting watts often set the generator size on their own. If you want the air conditioner on backup power, the generator must be able to start it. If you leave the air conditioner off backup power, a much smaller generator can cover the rest of the home.
What fuel does a Generac standby generator use?
Standby generators commonly run on natural gas or propane, depending on what is available at the home and what the generator model supports. Fuel availability, tank size for propane, and gas line capacity all affect the installation, so a provider should confirm fuel before sizing is finalised. Fuel type depends on your address and setup.
Do I need a permit for a generator installation?
In general terms, Florida Building Code 105.1 requires a permit before installing, altering, or replacing a regulated electrical system, and a generator installation with a transfer switch falls in that category. Whether the City of Fort Pierce or St. Lucie County handles your permit depends on your exact address. A provider should handle permit, utility, and inspection coordination as part of the job.
What is an automatic transfer switch, and do I need one?
An automatic transfer switch watches grid power and, when it fails, starts the generator and switches the home to generator power on its own, then switches back when grid power returns. It is what makes standby power automatic rather than manual. A standby generator installation normally includes one, sized for the circuits it backs up. Portable generators use a different setup and are a separate question.
How long does a generator installation take, and what should I plan for?
Timing varies with panel work, gas or propane work, placement, and permit and inspection scheduling, so no single timeline is promised here. Plan for a site assessment first, then installation, then inspection and testing. Your provider should confirm the timeline for your home, including any panel upgrade or transfer switch work that the sizing shows is needed, before work starts.
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