Whole-Home Generator Sizing Guide for Maryland & Northern Virginia

The right generator is the smallest one that runs your house comfortably. Here is how to actually size a standby unit for a DMV home - without paying for capacity you will never use.

Whole-home generator sales in the DMV move with the storm calendar. A big derecho or hurricane remnant drives a run of installs for the following six months, and then it quiets down until the next one. Along the way, plenty of homeowners end up with generators that are too big for what they actually need - which costs more to buy, more to install, more to service, and more to fuel. This guide walks through how a licensed electrician actually sizes a generator for a Maryland or Northern Virginia home in 2026.

Standby vs. portable - set that first

• Portable generator - 4–12 kW, wheeled, gas-powered, connected through an inlet and interlock or a manual transfer switch. Cheapest option. Runs a limited set of circuits. Requires the homeowner to be present to start and refuel.
• Standby generator - 10–26 kW, permanently installed, natural gas or propane, auto-starts on power loss via an automatic transfer switch (ATS). This is what most DMV homeowners mean by 'whole-home generator.'

Sizing math

A whole-home generator does not need to run every load simultaneously. It needs to run the loads you actually want during an outage - and to handle the start-up surge of the largest motor loads (typically your AC compressor and well pump if you have one).

Rough sizing by house profile (natural gas heat, standard DMV single-family):

• Under 2,000 sq ft, single AC, gas heat and water heater: 14 kW is typically comfortable.
• 2,000–3,500 sq ft, two AC systems, gas heat: 18 kW to 22 kW.
• Over 3,500 sq ft, or two AC + electric water heater + pool: 22 kW to 26 kW.
• All-electric home (heat pumps, electric water heater, EV): 26 kW minimum, load management required, sometimes two units in parallel.

Fuel choice - natural gas is usually the answer

Most of the DMV has natural gas at the curb. That is a big deal for a standby generator, because it removes the propane tank sizing question and gives the unit essentially unlimited runtime. Where natural gas is not available (rural Frederick, parts of Loudoun, some of Southern Maryland), propane is the fallback - plan on a 500-gallon aboveground tank at minimum for meaningful outage duration.

Transfer switch options

• Whole-home ATS with load management - the generator sees the whole panel. A load management module sheds non-essential loads (dryer, EV charger, second AC) if the unit is close to capacity. This is what we install by default on Generac units.
• Service-entrance ATS - replaces the main disconnect and integrates the transfer switch into the service equipment. Cleaner install, ideal on a service upgrade.
• Sub-panel / essentials-only - cheaper, but limits which circuits run on generator. Rarely worth the savings once you factor in future flexibility.

2026 install pricing in the DMV

• 18 kW Generac, natural gas, whole-home ATS with load management, 200A service, gas line within 20 feet: $10,500 – $14,500 all-in.
• 22 kW same setup: $12,000 – $16,000.
• 26 kW same setup: $14,500 – $18,500.
• Add a 200A service upgrade if needed: $1,200 – $2,500.
• Add a gas line extension if the meter is far from the generator location: $600 – $2,000 depending on distance and difficulty.

Permits and gas coordination

Generator installs require both an electrical permit and a mechanical/gas permit. Pirro pulls the electrical. The gas line work - if any - is coordinated with a licensed gas plumber. Washington Gas, BGE, and Pepco each have their own coordination for setback, meter clearance, and inspection.

Placement rules

• Minimum 18 inches from the house on the discharge side (manufacturer-specific; check the unit).
• Minimum 5 feet from any window or door opening.
• Minimum 3 feet from the gas meter.
• Concrete or composite pad, level.
• Accessible for service.

Maintenance is not optional

A standby generator that never runs is a standby generator that will not start when you need it. Annual service - oil, filter, spark plugs, transfer switch inspection - is the price of admission. Most manufacturers void the warranty without documented annual service. Every install we do goes on a service reminder.

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