Whole-House Generator Cost in Southern Maryland: 2026 Price Guide by Size and Fuel Type

By Gray & Sons Contracting · September 10, 2026

A whole-house standby generator in Southern Maryland costs $5,000 to $25,000 fully installed in 2026, with most homeowners in Calvert, St. Mary's, and Charles County paying $7,000 to $15,000 for a properly sized unit with an automatic transfer switch and a concrete pad. The national average runs about $7,500 to $15,000, and Southern Maryland falls right in that range, installation costs here are neither inflated nor discounted, but the need for a generator is higher than average because of where you live.

Southern Maryland sits in a corridor where tropical storms, nor'easters, and summer thunderstorms knock out power regularly. The rural stretches of Calvert, St. Mary's, and Charles County, places like Lusby, Solomons, St. Leonard, Hollywood, Piney Point, Ridge, and Nanjemoy, run on above-ground power lines through heavily wooded areas, which means a single downed tree can leave a neighborhood dark for days. Homes on well water and septic systems lose not just lights and heat but running water and sewage function when the power goes out. A standby generator is not a luxury in those areas, it is the system that keeps the house functional.

Here is what a whole-house generator actually costs in Southern Maryland, how to size one correctly, what fuel type makes sense for your property, and what the installation involves.

Generator Cost by Size

The size of a standby generator is measured in kilowatts (kW), and the right size depends on what you need to power during an outage. A generator that is too small will overload and shut down. A generator that is too large wastes money on capacity you will never use.

The "installed cost" column includes the generator unit, the automatic transfer switch, the concrete or composite pad, gas line or propane hookup, electrical connections, permits, and labor. Installation typically adds $3,000 to $7,000 to the unit price depending on the complexity of the electrical work and the fuel connection.

For the typical Southern Maryland home, a 1,500- to 2,500-square-foot single-family house in Waldorf, Prince Frederick, Lexington Park, La Plata, California, or Leonardtown with one central HVAC system, a well pump, and standard appliances, a 20 kW generator covers the entire house. That is the most commonly installed size in this market, and the $9,000 to $14,000 installed price is the realistic middle of the range for a quality unit from a major manufacturer with a proper installation.

Generator Cost by Fuel Type

Standby generators run on natural gas, liquid propane (LP), or diesel. The fuel type affects the upfront cost, the operating cost, the maintenance requirements, and, critically in Southern Maryland, whether the fuel is even available at your property.

Propane (LP Gas)

Unit cost premium: $0 (propane is the standard configuration for most residential standby generators) Fuel cost: $2.50 to $3.50 per gallon. A 20 kW generator burns roughly 2 to 3 gallons per hour under load. Operating cost during an outage: $5 to $10 per hour, or $120 to $240 per day at full load.

Propane is the default fuel for standby generators in Southern Maryland because most of the tri-county area, including all of Calvert County south of Dunkirk, all of St. Mary's County, and most of Charles County south of Waldorf, does not have natural gas service. Propane requires a storage tank on the property, and the size of that tank determines how long the generator can run before a refill.

The tank question. If you already heat with propane, and many homes in Calvert and St. Mary's County do, your existing tank may be large enough to supply both the furnace and the generator, with a dedicated generator connection added to the existing tank. If the existing tank is too small (a 120-gallon tank that already runs low during heating season will not support a generator too), you need a larger tank or a second dedicated tank. If you do not currently have propane on the property, the tank is a new installation that adds $800 to $2,500 to the project (or free with a lease agreement, which locks you into buying fuel from one supplier at their price).

A 500-gallon tank is the right size for a whole-house generator in Southern Maryland. It provides 8 to 10 days of continuous runtime at full load, enough to get through an extended outage from a hurricane or ice storm, and it is large enough that you are not calling for emergency refills during the same storm that knocked out your power. A 250-gallon tank is the minimum; a 120-gallon tank is inadequate for anything longer than a two-day outage.

Natural Gas

Unit cost premium: $0 to $500 more than propane for a dual-fuel unit. Fuel cost: $1 to $2 per therm. A 20 kW generator uses roughly 2 to 3 therms per hour. Operating cost during an outage: $3 to $6 per hour, or $72 to $144 per day at full load.

Natural gas is the cheapest fuel to operate and requires no on-site storage, the supply is continuous from the utility. The major advantage is unlimited runtime: as long as the gas utility has supply (and gas mains are underground, so they are far more outage-resistant than the electric grid), the generator runs indefinitely.

The limitation in Southern Maryland is availability. Natural gas service from Southern Maryland Gas (Washington Gas) is available in parts of Waldorf, La Plata, St. Charles, White Plains, Indian Head, and some areas of Calvert County near Prince Frederick and Dunkirk. Most of St. Mary's County and rural Calvert and Charles County do not have natural gas access. If your property has a gas meter or is on a street with a gas main, natural gas is the best fuel choice for a standby generator. If not, propane is your option.

The gas line. Connecting a standby generator to natural gas requires a dedicated gas line from the meter to the generator pad, sized to deliver the BTU load the generator requires at full output. A 20 kW generator needs roughly 200,000 BTU per hour of gas supply, which typically requires a 1-inch or 1.25-inch gas line. If the existing gas meter and supply line are undersized for the added load, the utility may need to upgrade the meter and the service line, which is usually free from the utility but takes scheduling. The gas line from the meter to the generator pad costs $500 to $2,000 depending on the distance (typically 15 to 50 feet) and whether the line runs underground or along the exterior of the house.

Diesel

Unit cost premium: $2,000 to $5,000 more than an equivalent propane unit. Fuel cost: $3.50 to $5 per gallon. Operating cost during an outage: $7 to $15 per hour, or $168 to $360 per day at full load.

Diesel generators are built for heavy, continuous use, they last longer than gas-fueled units and handle sustained load better. They are also louder, more expensive, require more maintenance (fuel filters, injectors, fuel stabilizer for stored diesel), and produce exhaust that needs to be vented away from windows and living areas. Diesel is the standard for commercial and agricultural standby power, but for residential use in Southern Maryland, propane and natural gas are the better choices in almost every case.

The one scenario where diesel makes sense is a large property with no propane infrastructure and no natural gas, where the homeowner already has diesel fuel storage for farm or marine equipment. Some waterfront properties on the Chesapeake in St. Mary's and Calvert County fit this profile.

Generator Cost by Brand

Three manufacturers dominate the residential standby generator market. All three are available through dealers in Southern Maryland, and all three produce reliable units, the differences are in features, warranty coverage, and dealer network density.

Generac holds roughly 70 to 80 percent of the residential standby market and has the densest dealer and service network in Southern Maryland. That matters because a generator that needs warranty service from a dealer three counties away is a generator that sits broken during the next outage. If your local dealer is a Generac dealer, and in Calvert, St. Mary's, and Charles County, most are, Generac is the practical choice for parts availability and service response time.

Kohler is the premium alternative with a quieter unit and a more weather-resistant enclosure. For waterfront homes in Solomons, Chesapeake Beach, St. George Island, and Piney Point where salt air corrosion is a concern, Kohler's marine-grade enclosure has an edge.

What the Installation Involves

A standby generator is not a plug-in appliance. The installation is a permitted electrical and mechanical project that takes one to three days of on-site work, plus scheduling lead time for permits, equipment delivery, and (for natural gas) utility coordination.

The Automatic Transfer Switch

Cost: $500 to $2,000, included in most installed prices.

The automatic transfer switch (ATS) is the device that monitors utility power and switches the house to generator power within seconds of an outage, typically 10 to 30 seconds. When utility power returns, it switches back and shuts the generator down. The ATS is installed at or near the main electrical panel.

There are two types:

Whole-house ATS ($800 to $2,000): Powers the entire electrical panel. Every circuit in the house switches to generator power. This requires a generator large enough to carry the full electrical load, typically 20 kW or larger.

Load-shedding or managed ATS ($500 to $1,500): Prioritizes critical circuits and cycles non-essential loads on and off to stay within the generator's capacity. This allows a smaller generator (14 to 16 kW) to cover a house that would otherwise need a 22 kW unit, saving $1,000 to $3,000 on the generator. The trade-off is that some circuits, the electric dryer, the pool pump, the second HVAC zone, may cycle off temporarily under heavy load.

The Generator Pad

Cost: $200 to $800.

The generator sits on a level pad adjacent to the house, typically within 5 feet of the exterior wall nearest the electrical panel, but at least 5 feet from any window, door, or opening (per code and manufacturer requirements, because the exhaust contains carbon monoxide). The pad is either a poured concrete slab (4 inches thick, reinforced, $400 to $800) or a prefabricated composite pad ($200 to $400). Composite pads are lighter and faster to install; concrete pads are more permanent and handle heavier units better.

Placement matters. The generator should be positioned where exhaust and noise do not impact the living areas or the neighbors, where it is accessible for maintenance, and where it does not violate setback requirements. In Southern Maryland, county code and manufacturer guidelines both require minimum distances from windows, doors, vents, and property lines, typically 5 feet from the house and 18 inches from any wall without an opening. Your contractor should confirm placement with the local building department before pouring the pad.

Electrical Work

Cost: $1,500 to $4,000, included in most installed prices.

The electrical work includes:

• Installing the automatic transfer switch at the main panel
• Running a power cable from the generator to the transfer switch (typically 6/3 or 4/4 copper cable in conduit)
• Installing a disconnect switch at the generator per code
• Bonding and grounding the generator per NEC requirements
• For load-managed systems: identifying and wiring the priority circuits

If the main electrical panel is full, common in homes built in the 1980s and 1990s with 100A or 150A service, the installation may require a subpanel or a panel upgrade ($1,000 to $2,500) to accommodate the transfer switch. If the service entrance is 100A and the generator is 20 kW or larger, a service upgrade to 200A ($2,000 to $4,000) may be recommended to handle the full load safely.

Gas Line or Propane Connection

Cost: $500 to $2,500.

For propane: a dedicated line from the existing tank to the generator, with a regulator sized for the generator's BTU demand. If a new propane tank is needed, that is an additional cost (see the propane section above).

For natural gas: a dedicated line from the gas meter to the generator pad, sized to the generator's BTU demand. The gas utility may need to upgrade the meter, contact them before scheduling the installation.

Permits

Cost: $200 to $500.

A standby generator installation requires an electrical permit and may require a mechanical or gas permit depending on the county and the scope of the fuel connection. Calvert, St. Mary's, and Charles County each have their own permit process, and the turnaround time for plan review and inspection scheduling varies. Budget 1 to 4 weeks for the permit process, though some counties offer expedited review.

The permit covers the electrical connection (transfer switch, grounding, disconnect), the fuel connection (gas line or propane piping), and the placement (setbacks, noise, exhaust clearance). An unpermitted generator installation is a code violation that can complicate insurance claims and home sales.

The Total Installation Cost Breakdown

Here is what a typical 20 kW propane standby generator installation looks like for a 2,000-square-foot home in Southern Maryland:

Add $800 to $2,500 if a new propane tank is needed. Add $1,500 to $4,000 if the electrical panel needs upgrading. Add $500 to $2,000 for a natural gas line if you are in a gas service area and do not have an existing connection near the generator location.

Sizing Your Generator Correctly

Sizing is not about guessing, it is about adding up the wattage of everything you want to run simultaneously and then adding a margin for motor starting surges. Here is how it works.

Step 1: List Your Loads

Every electrical device in your house has a running wattage (what it uses continuously) and a starting wattage (the surge it draws when it first turns on, motors can draw 3 to 5 times their running wattage at startup).

Step 2: Add the Running Watts, Then Account for Starting Surges

Add the running wattage of everything you want powered simultaneously. Then identify the largest motor load (usually the central AC or well pump) and add its starting surge on top. That total is your minimum generator capacity.

Example for a typical Southern Maryland home:

• Central AC: 3,500W running
• Well pump: 1,000W running
• Refrigerator + freezer: 500W running
• Lights: 800W running
• Kitchen appliances (microwave, range): 2,500W running
• Washer: 500W running
• Electronics: 400W running
• Water heater: 4,500W running
• Total running: 13,700W
• Plus AC starting surge: 7,000W
• Peak demand: 20,700W (roughly 21 kW)

A 22 kW generator covers this comfortably. A 20 kW generator covers it with a load-managed transfer switch that staggers motor startups. A 16 kW generator cannot carry it all at once, you would need to decide what stays off during peak load.

Step 3: Round Up, Do Not Round Down

Generator sizing is one of those decisions where "close enough" is not close enough. An undersized generator overloads, trips its breaker, and shuts down, typically at the worst possible moment, during a storm, in the dark, when the AC and the well pump and the sump pump are all trying to run at once. Buy one size larger than your calculation suggests. The $500 to $1,000 difference between a 20 kW and a 22 kW unit is cheap insurance against a midnight shutdown.

Why Southern Maryland Homeowners Need Generators More Than Most

The power grid in Southern Maryland is more vulnerable to extended outages than urban and suburban grids for several specific reasons.

Above-ground lines through dense tree canopy. The overhead distribution lines through Calvert, St. Mary's, and Charles County run through miles of mature forest. Every storm drops branches on lines, and major storms drop whole trees. SMECO (Southern Maryland Electric Cooperative), the utility serving most of the tri-county area, has invested heavily in vegetation management and line hardening, but the geography limits what hardening can achieve.

Long restoration times. When a storm takes out a main feeder line serving a rural area, a stretch of Route 4 south of Prince Frederick, Route 235 through Lexington Park, Route 5 through Mechanicsville, every home downstream goes dark until that main line is restored. In major events (hurricanes, ice storms, severe thunderstorm derechos), restoration can take 3 to 7 days. The 2012 derecho left parts of Southern Maryland without power for over a week. Hurricane Isabel in 2003 knocked out power for up to two weeks in some areas.

Well water and septic dependence. Most homes in Calvert County, St. Mary's County, and rural Charles County are on well and septic systems. When the power goes out, the well pump stops, which means no running water, no flushing toilets, and no showers. A generator is not just powering lights and AC; it is keeping the basic water supply running.

Sump pump reliance. Many homes in low-lying areas, Chesapeake Ranch Estates, parts of Lusby, waterfront communities in St. Mary's, rely on sump pumps to keep basements and crawl spaces dry. The power outage happens during the same storm that sends water toward your foundation. Without a generator, the sump pump stops exactly when it is needed most.

Home-based work. The post-2020 shift to remote work means a power outage is now an income outage for many households. NAS Patuxent River supports thousands of civilian contractors and military families in St. Mary's and Calvert County, many of whom work remotely or have home offices. A generator keeps the internet (assuming a battery-backed modem or fiber ONT), the computer, and the phone system running during an outage.

Maintenance and Operating Costs

A standby generator is a machine with an engine, and like any engine, it requires regular maintenance to run reliably when called upon.

Annual maintenance cost: $250 to $600 per year. Most manufacturers and dealers offer annual service plans that include one or two visits per year for $250 to $400, a good investment because a generator that sits for 11 months and then needs to start during a January ice storm had better start on the first crank.

The weekly exercise cycle. Modern standby generators run an automatic exercise cycle, typically 15 to 20 minutes once a week, to keep the engine, battery, and oil circulated. This runs at no-load or light load and burns a small amount of fuel (less than half a gallon per cycle). Do not disable this cycle. It is what keeps the generator ready to start when called.

Portable Generators vs. Standby Generators

Portable generators cost $500 to $3,000 and provide 3,000 to 12,000 watts of power. They are cheaper upfront but have significant disadvantages for whole-house backup.

Portable generators have their place, for camping, for a job site, for a short outage where you just need to keep the refrigerator and a few lights on. But for a Southern Maryland home on well water where outages last days, a standby generator is a different category of protection.

The carbon monoxide warning is not theoretical. Generator-related carbon monoxide poisoning kills an average of 70 to 80 people per year in the United States, nearly all from portable generators run too close to the house, inside a garage, on a covered porch, or near an open window. A permanently installed standby generator eliminates this risk because its placement is engineered and permitted to keep exhaust away from the living space.

The Return on Investment

A standby generator adds $3,000 to $5,000 to home resale value, roughly 30 to 50 percent of the installed cost for a standard system. But the real return is measured in what it prevents:

• A flooded basement from a failed sump pump during a storm costs $5,000 to $25,000 in water damage restoration
• A refrigerator and freezer full of spoiled food costs $500 to $1,500 per event
• A burst pipe from a frozen house during a winter outage costs $2,000 to $10,000 in plumbing and water damage
• A missed week of remote work during an extended outage costs whatever your weekly income is

One major prevented event can repay the entire cost of the generator. In a region where multi-day outages happen every few years, the question is not whether the generator pays for itself but how quickly.

Frequently Asked Questions

How long does a standby generator last? A quality standby generator (Generac, Kohler, Cummins) lasts 15 to 30 years with regular maintenance. Air-cooled units (most residential models under 26 kW) tend to last 15 to 20 years. Liquid-cooled units (typically 30 kW and above) can last 25 to 30 years because the engine runs cooler under load. The most common failure point is not the engine, it is the battery. Replace the battery every 3 to 4 years and keep up with oil changes, and the generator will outlast the roof on your house.

How loud is a standby generator? Most residential standby generators produce 55 to 70 decibels at 23 feet, comparable to a normal conversation or a dishwasher running. That is significantly quieter than a portable generator (65 to 80 dB, comparable to a vacuum cleaner or a lawn mower). Noise levels vary by brand and size: Kohler units are generally the quietest, followed by Cummins, then Generac. At typical setback distances (10 to 20 feet from the house), the generator is audible but not disruptive indoors.

Can I install a standby generator myself? No. A standby generator installation requires a licensed electrician for the transfer switch and wiring, a licensed plumber or gas technician for the fuel connection, and a permit from the county. The electrical work, connecting a transfer switch to a live main panel, is not a DIY task. An improper installation creates a backfeed hazard that can electrocute utility workers restoring power to your line, which is why code requires a properly installed transfer switch and why the installation must be inspected.

Do I need a concrete pad? You need a level, stable surface that supports the weight of the generator (400 to 600 pounds for a 20 kW unit) and keeps it above grade. A poured concrete pad is the most durable option. Prefabricated composite pads (GenPad, for example) are lighter and faster to install. Either is acceptable, the key requirement is that the pad is level and sits on compacted ground that will not settle. Do not set a generator on pavers, gravel, or bare ground.

What happens to the generator during a flood? If the generator pad floods, the generator will likely be damaged, electrical components, the control board, and the engine intake are all at risk. For homes in flood-prone areas, the generator pad should be elevated above the base flood elevation. A raised pad or a platform adds $500 to $1,500 to the installation but protects a $10,000+ investment. For homes in FEMA flood zones along the Patuxent River, the Chesapeake Bay, and the tidal creeks in St. Mary's and Calvert County, elevation is not optional.

Will my HOA allow a standby generator? Most HOAs in Southern Maryland allow standby generators but may have requirements for placement, screening, and noise. Check your HOA covenants before scheduling the installation. Common restrictions include minimum setbacks from property lines (often 5 to 10 feet beyond what code requires), sound barriers or fencing to screen the unit, and approved colors for the enclosure. An HOA that prohibits generators entirely is rare in this area, but it is worth confirming before you sign a contract.

Thinking about a whole-house generator? Gray & Sons Contracting has been keeping Southern Maryland homes running through storms for 50 years. We will size the generator to your house, handle the electrical and gas connections, pull the permits, and make sure it starts the first time you need it. Get a Free Estimate