Estimated Read Time: 9 minutes
A winter ice storm or summer thunderstorm can flip your life off in seconds. If you want backup power that actually matches your home, you must choose the right size whole house generator. This guide explains a simple sizing path, real‑world examples, and local tips for Southwest Virginia homes so you never overspend or get stuck with a system that trips the moment your heat pump starts. Get expert help, fast installs, and pro maintenance from Bob Garrett Services.
Why generator size matters in Southwest Virginia
Power outages in the Roanoke Valley often come with ice, wind, and long utility restoration times. Undersizing means lights flicker, the heat pump stalls, and refrigerators struggle. Oversizing wastes budget and fuel, and can push you into gas meter or tank upgrades you do not need.
The right size balances running watts, starting surges, and your actual lifestyle. It also considers fuel supply, runtime goals, and noise placement. Our team sizes and installs Generac and Kohler systems daily across Roanoke, Salem, Christiansburg, and the lakes. We combine field data with manufacturer specs, then fine‑tune with load management so you get reliable power without guesswork.
Step 1: Decide essential circuits vs. whole‑home coverage
Start by choosing between two approaches.
- Essential circuits
- Keeps the must‑haves on: fridge, freezer, well pump or sump, a few outlets, lighting, Wi‑Fi, and either a furnace blower or one small heat pump air handler.
- Best for tight budgets or homes with propane limitations.
- Whole‑home coverage
- Powers the entire main panel, including HVAC, cooking, laundry, and EV charging when managed correctly.
- Ideal for households that work from home, have medical equipment, or experience frequent multi‑day outages.
If you are unsure, we often design for essential loads but specify a generator and transfer switch that can be expanded to whole‑home later. Load‑shedding modules make this flexible without replacing the entire system.
Step 2: Calculate running watts and starting watts
Every appliance lists running watts. Motors and compressors also need extra starting watts for a few seconds. Your generator must cover both at once or use smart load management to stage startups.
- Running load example
- Refrigerator: 700 watts
- Gas furnace blower: 600 watts
- Sump or well pump: 1,000 watts
- Lighting and outlets: 800 to 1,200 watts
- Starting surges
- 2 to 3 times the running watts for pumps and compressors.
A typical essentials package often lands between 5 kW and 10 kW. A full‑size heat pump or a deep well pump can add 3 to 7 kW of surge. This is why a 10 kW unit can be perfect for some homes, while a 22 to 26 kW unit is a better fit for others.
Step 3: Choose fuel type and runtime goals
Fuel choice affects size, runtime, and project scope.
- Natural gas
- Convenient and continuous supply for many Roanoke and Salem neighborhoods.
- Utility meter capacity must support generator demand plus other appliances.
- Propane (LP)
- Common in Franklin and Bedford County and at Smith Mountain Lake.
- Tank size sets your runtime. Many homeowners select 250 to 500 gallons to cover multi‑day outages.
Runtime goal matters. If you want 48 to 72 hours without delivery, we balance fuel consumption with size, load management, and thermostat settings. Bigger is not always better if your tank is small.
Step 4: Load management and transfer switches
Modern standby systems use smart transfer switches and load‑shedding modules to control surges and protect the generator. This allows a right‑sized unit to handle large loads without oversizing.
- Smart switching
- Staggers heavy startup loads so compressors do not hit at once.
- Prioritizes critical circuits before comfort loads.
- Practical result
- A properly managed 18 to 22 kW generator can power many 2,000 to 3,000 sq. ft. homes comfortably.
Generac and Kohler both offer automatic operation. Generac’s Mobile Link remote monitoring and Kohler’s OnCue Plus let you check status from your phone. Kohler’s automatic transfer can restore power in 10 seconds or less, reducing light flicker and HVAC nuisance trips.
Step 5: Sizing examples using popular models
Examples help translate theory to your home. Here are two real‑world benchmarks we install often.
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Essential circuits and small HVAC air handler
- Typical outcome: 8 to 12 kW
- Model example: Generac Guardian 10 kW Wi‑Fi Enabled, Model #7171
- Notes: Supports fridge, lights, outlets, well or sump pump, network gear, and a small air handler with smart load management.
-
Whole‑home coverage for larger HVAC and kitchen
- Typical outcome: 22 to 26 kW
- Model example: Generac Guardian 26 kW with transfer switch, Wi‑Fi Enabled, Model #7291
- Notes: Handles most homes up to 3,500 sq. ft. with electric range and dryer when loads are staged. Great fit for families who cannot pause during an outage.
Remember that square footage alone is not a sizing tool. We assess HVAC tonnage, pump horsepower, well depth, water heater type, EV chargers, and workshop tools. Then we apply starting surge math and select the right transfer gear.
Step 6: Placement, noise, and local permitting
Proper placement protects your family and investment.
- Location
- Place on a stable pad outside, clear of snow‑shedding rooflines and heavy runoff.
- Respect clearances to windows, doors, and vents. We follow manufacturer instructions and local code during site survey.
- Sound
- Newer air‑cooled units are impressively quiet for neighborhoods like South Roanoke and Cave Spring. Weekly exercise runs are short and can be scheduled.
- Permits and utility coordination
- We handle electrical and gas permits and coordinate with Appalachian Power or Roanoke Gas when required. Inspections are scheduled for you.
Our crews also handle trenching and backfill when needed, and we restore disturbed areas neatly. After heavy rain, we return to re‑pack if needed to prevent washouts.
Step 7: Brand features that influence the size you choose
Features can improve performance without upsizing.
- Automatic operation
- Both brands start within seconds of a power outage. No manual action required.
- Remote monitoring
- Generac Mobile Link and Kohler OnCue Plus let you see status, alerts, and maintenance from anywhere.
- Warranty confidence
- Kohler offers a 5‑year, 2,000‑hour limited warranty on many models. Strong support helps protect your investment.
Because we are factory‑trained on Generac and Kohler, we match features to your priorities. If you travel often, monitoring is a must. If you have a sensitive home office, faster transfer and clean voltage regulation matter more than chasing the largest kW number.
Step 8: Maintenance and ownership costs by size
Every generator needs routine maintenance. Larger units hold more oil and run more circuits, so care matters.
- Routine items
- Oil and filter changes, air filter, spark plugs, valve checks per manufacturer guidance.
- Exercise run checks, battery testing, and firmware updates for monitoring modules.
- Service quality
- Our certified technicians maintain to factory specifications and brief you on findings. Customers consistently note thorough work and clear explanations.
Planned maintenance keeps your system ready. It also validates warranty requirements and catches small issues before storm season. Many homeowners schedule annual service, often before summer and winter peak outage periods.
Step 9: Budget, financing, and project timeline
Sizing affects project cost, gas work, and panel upgrades. We build options so you can compare essential‑only vs whole‑home with and without load management.
- Financing
- We partner with GoodLeap to offer flexible payment options for your project.
- Timeline
- Bob Garrett Services can get your generator installed now with no waiting. Most installs complete in about a day once permits and gas work are ready.
- Handover
- We commission the system, walk you through operation and best practices, and set up your remote monitoring app.
Our proven sizing and installation process
As the largest residential generator dealer in Southwest Virginia, we follow a consistent, homeowner‑friendly process.
- Free expert consultation
- Virtual or in‑home assessment of loads, lifestyle, and outage history.
- Custom sizing and proposal
- We model running and starting loads, then present two to three options with and without load management.
- Turnkey installation
- Transfer switch, panel work, gas coordination, trenching, pad, and start‑up.
- Briefing and documentation
- You get a clear walkthrough, app setup, and a maintenance plan tailored to your model.
- Responsive service and repairs
- Factory‑trained techs maintain and repair Generac and Kohler units to spec.
Two hard facts that matter for reliability
- Kohler’s automatic transfer can restore power in 10 seconds or less.
- Kohler offers a 5‑year, 2,000‑hour limited warranty on many standby models. Generac Guardian models like the 10 kW #7171 and 26 kW #7291 are Wi‑Fi enabled for easy monitoring.
With the right size and a quality install, your home stays warm, connected, and protected through any outage in the Blue Ridge.
Special Offer: Free Standby Generator Consultation and Estimate
Ready to size it right? Schedule your Free Virtual Home Consultation and get a no‑obligation estimate for Generac or Kohler installation. Call 540-583-4765 or visit https://bobgarrettservices.com/ to book your appointment today.
What Homeowners Are Saying
"Very impressed by Bob Garretts crew. Installed a 24 kw generator in one day, everything went smooth, communication which is key to any project was excellent. I will be passing on my 5 Star recommendations to the neighbors, this is the way projects should be done. Thanks to Bob Garret and his crew, they were outstanding."
–John F., Installation
"Jon came out to give us a quote and discuss our placement options for a new generator. He was polite, patient with our questions, and promptly sent me a quote, which we accepted. When the date for the installation came, a very professional crew showed up as promised and installed the generator. The installers were very friendly, and took extra time to show me the features and best practices for the unit."
–Christine C., Installation
"Colin came to do maintenance on our generator today. He did a fantastic job. He didnt mind me asking questions and showing me the parts he replaced. He was very thorough and made sure all was clean when putting up. I told him I will be looking forward to seeing him next year on schedule. I love my Generac and thank Bob Garrett Services."
–Just L., Maintenance
Frequently Asked Questions
How big should my whole house generator be?
Most homes land between 10 kW and 26 kW. The exact size depends on HVAC tonnage, pumps, cooking, laundry, and whether you want essential circuits or whole‑home coverage.
Can load management let me buy a smaller generator?
Yes. Smart transfer switches and load‑shedding modules stagger heavy startups. This often lets a right‑sized 18 to 22 kW unit handle larger homes comfortably.
How long does installation take?
After permits and gas coordination, most installations finish in about one day. We commission the system and brief you on operation before we leave.
What fuel should I choose, natural gas or propane?
Use natural gas if available. For propane, we size the tank to your runtime goals. Many homeowners select 250 to 500 gallons for multi‑day outages.
What warranties are available?
Kohler offers a 5‑year, 2,000‑hour limited warranty on many models. Generac and Kohler both include strong factory support and remote monitoring options.
Conclusion
Choosing the right size whole house generator protects your comfort, food, and work during outages. With accurate load math, smart management, and a quality install, your system starts fast and runs smoothly. For expert sizing in Southwest Virginia, trust Bob Garrett Services, the local leader in Generac and Kohler solutions.
Call, Schedule, or Chat
- Call now: 540-583-4765
- Schedule online: https://bobgarrettservices.com/
- Special: Book your Free Virtual Home Consultation and estimate today. Get the right size, a clear price, and a fast install across Roanoke, Salem, Vinton, Christiansburg, and more.
Bob Garrett Services is Southwest Virginia’s largest residential generator dealer. Our factory‑trained electricians sell, install, and service Generac and Kohler whole‑home systems. We handle load sizing, permits, trenching, transfer switches, and remote monitoring. Backed by manufacturer training, strong warranties, and responsive maintenance, we deliver fast, no‑wait installs, clear communication, and fair pricing. Proudly serving Roanoke, Salem, Vinton, Blacksburg, and nearby communities with dependable standby power and five‑star service.