Whole-House vs. Partial Backup: Which Do You Actually Need?
The biggest decision in a residential generator project is not what brand to buy. It's whether you want the house to run normally during an outage or just keep the essential systems alive. That decision drives the size, the transfer switch design, and a significant chunk of the cost.
Partial backup means you back up specific circuits — typically the sump pump, refrigerator, freezer, a few lights, a window A/C unit, and basic outlets in bedrooms and the kitchen. A 11kW to 14kW generator with a load-management transfer switch handles this. During an outage, the generator runs those circuits and nothing else. The furnace or central A/C is not covered unless specifically included. The electric stove might not work. Cost for a complete partial-backup install in Nassau or Suffolk typically runs $5,500 to $9,000.
Whole-house backup means the house keeps running exactly as it did on grid power — central A/C, all appliances, every circuit. This requires a 22kW or larger generator with a 200-amp automatic transfer switch. During an outage, you literally may not notice the power switched over unless you're paying attention. Cost for a complete whole-house install in Nassau or Suffolk typically runs $9,000 to $14,000.
The right choice depends on your household. Families with small children or elderly members who need climate control tend to prioritize whole-house coverage. Homeowners whose main concern is the sump pump and refrigerator often find partial backup sufficient. The determining question: during a 5-day outage in July, what happens to your family without A/C? If the answer is "we go to a hotel," partial backup may be fine. If the answer is "we can't leave and someone could have a health problem," whole-house coverage is the right investment.
Generator Sizing Guide for Long Island Homes by Square Footage
Online sizing guides often oversimplify. The real answer is that two homes with the same square footage can have very different electrical loads depending on HVAC type, water heating, and whether there's a well pump or a pool. That said, here is a practical starting point for Long Island homes.
| Home type / size | Coverage goal | Recommended size |
|---|---|---|
| Ranch, 1,200–1,800 sq ft | Essential circuits only | 11kW–14kW |
| Ranch or split-level, 1,800–2,500 sq ft | Whole-house, central A/C | 18kW–22kW |
| Colonial or hi-ranch, 2,000–3,500 sq ft | Whole-house, central A/C | 22kW |
| Large colonial, 3,500+ sq ft | Whole-house + pool or EV | 26kW–36kW |
| Any size with heat pump heating | Whole-house year-round | 26kW minimum |
These are starting points, not final answers. If you have a well pump (common in parts of Suffolk), add 1kW to 2kW. If you have an electric hot water heater instead of gas, add 3kW to 4kW. If you want to run an EV charger during outages, add 7kW to 10kW depending on the charger level.
The reason we run a load calculation on every job is that an undersized generator causes problems. If the generator trips on overload during an outage, you're no better off than if you'd never bought it. Oversizing wastes money and burns more fuel. The load calc takes about 20 minutes and eliminates the guesswork.
Propane vs. Natural Gas for Long Island Standby Generators
Most Long Island homeowners who have never had to think about generator fuel get surprised when this comes up. Here is the full picture.
Natural gas availability on Long Island: National Grid provides gas service to most of Nassau County and a large portion of western and central Suffolk County — Babylon, Islip, Huntington, parts of Smithtown and Brookhaven. If your furnace, water heater, or stove runs on gas, you have a National Grid service and can run a standby generator off it with a gas line extension.
Areas without gas service on Long Island include much of eastern Suffolk — Riverhead, Southold, East Hampton, Southampton — as well as Fire Island, some barrier beach communities in Nassau, and pockets of North Shore villages where gas never got extended. These homes rely on oil heat and propane for cooking, and propane is also the generator fuel of choice.
Choosing natural gas when available: Natural gas wins on convenience and economics for most homeowners. The fuel is piped in — it never runs out during an outage as long as the gas infrastructure is intact (National Grid gas lines rarely go down during weather events that knock out PSEG electric service). You don't have to monitor fuel level or schedule deliveries. Per-BTU cost is lower than propane in most cases. The only potential issue is that during a major regional disaster, if National Grid's gas service is interrupted, you lose generator fuel too. This is rare but worth knowing.
Choosing propane: For homes without gas service, propane is the standard answer. You'll need a dedicated propane tank — typically 250 gallons for smaller generators on essential circuits, 500 to 1,000 gallons for whole-house systems. Tank rental through a local Long Island propane supplier (Paraco, Amerigas, and others serve the area) runs $300 to $500 per year for a 500-gallon tank. Fuel cost at current Long Island propane prices runs roughly $2.50 to $3.50 per gallon. A 22kW generator running at 50% load burns about 2 gallons per hour, so a 500-gallon tank gives you roughly 8 to 10 days of runtime.
Battery backup vs. generator for shorter outages: Some Long Island homeowners ask whether a whole-home battery system like a Tesla Powerwall or Enphase IQ Battery is an alternative to a standby generator. The honest answer is that batteries work well for outages measured in hours — a typical 4-hour nor'easter interruption, for example. But for the 3-day to 10-day outages that Long Island has experienced after Sandy, Isaias, and Ida, battery capacity runs out long before grid power is restored. Unless paired with a large solar array, battery systems are not a complete replacement for a gas standby generator for Long Island households planning for major storm events.
Standby Generator Cost Comparison on Long Island
Here is a realistic cost comparison for complete standby generator installations across Long Island, including generator, transfer switch, concrete pad, gas or propane line, labor, and permits.
| Configuration | Nassau County | Suffolk County |
|---|---|---|
| 11kW essential circuits, natural gas | $5,500–$8,000 | $5,200–$7,500 |
| 11kW essential circuits, propane | $6,500–$9,000 | $6,200–$8,500 |
| 22kW whole-house, natural gas | $9,000–$13,000 | $8,500–$12,000 |
| 22kW whole-house, propane | $10,500–$14,500 | $10,000–$14,000 |
| 26kW+ large home, natural gas | $12,000–$18,000+ | $11,500–$17,000+ |
Nassau County permit fees tend to run slightly higher than Suffolk County towns, which accounts for the modest price difference. Propane installs cost more upfront because of propane tank coordination and often longer gas line runs.
These numbers assume a straightforward installation with good generator placement access, a gas meter within 25 feet of the generator location, and no panel upgrade required. If you need a 100A to 200A panel upgrade at the same time — which comes up on about a third of Nassau County generator jobs in older housing stock — add $3,500 to $6,000 to those numbers, though combining the jobs is more efficient than doing them separately.
Generator Permit Process: Nassau County vs. Suffolk County
Permitting is one of the main reasons generator installations on Long Island take longer than homeowners expect. Here is how it works in each county.
Nassau County: You need three permits in most cases — an electrical permit for the transfer switch and wiring, a gas permit for the gas line, and a building permit for the concrete pad and equipment placement. If you live in an incorporated village (Garden City, Freeport, Hempstead, Long Beach, Rockville Centre, Valley Stream, and others), your permits go through the village building department. Unincorporated Nassau — Levittown, Massapequa, Plainview, Hicksville, East Meadow, Wantagh, and others — goes through Nassau County Buildings at One Michels Drive in Bethpage. Processing time runs two to four weeks.
Suffolk County: Permits are handled by the individual towns — Babylon, Brookhaven, Huntington, Islip, Smithtown, Riverhead, and others. Each town has its own building department, permit fees, and processing timeline. Suffolk towns generally process electrical and building permits separately. Gas permits in Suffolk go through the town, not the county. Timeline is similar to Nassau — two to four weeks in most cases, longer in summer.
PSEG interconnection: Both Nassau and Suffolk County installations require notification to PSEG Long Island before connecting an automatic transfer switch to their grid. This is a safety requirement under PSEG's interconnection standards. We file the interconnection notification as part of every generator install. PSEG does not physically inspect residential generator installations, but they do require the filing, and the final inspection by the local building department generally confirms the PSEG requirements are met.
We see homeowners get tripped up most often when they try to get quotes from installers who say permits aren't needed. On Long Island, they always are for a permanently installed standby generator. If something goes wrong with an unpermitted generator — a fire, a carbon monoxide event, a backfeed injury to a utility worker — your homeowner's insurance has grounds to deny coverage. We pull every permit and handle every inspection on every job.
How Long Does a Whole-House Generator Installation Take on Long Island?
The physical installation of a whole-house standby generator takes one to two days for most Long Island homes. The full timeline from decision to running generator is typically two to four weeks, driven almost entirely by the permitting and equipment delivery timeline.
Here is a realistic project timeline:
- Day 1–3Walk-through, load calculation, written quote. Most customers get their quote within 48 hours of the site visit.
- Day 4–7Contract signed. We file permits with the appropriate municipality and order the generator and transfer switch.
- Day 7–25Permit processing. Nassau County and Suffolk towns take two to four weeks. Generator and ATS arrive from distributor (usually one to two weeks).
- Day 25–28Install day(s). Concrete pad, gas line, generator set, transfer switch, wiring, commissioning. One to two days depending on scope.
- Day 28–35Final inspection by building department. We schedule it; you don't need to be home in most cases. Green tag issued, PSEG notified, project complete.
Plan for three to five weeks total in normal conditions. In the fall after a storm season, or during the summer permit-office rush, add one to two weeks. We give you a realistic timeline before you sign anything.
If you're also planning a Level 2 EV charger installation, adding it to the same permit pull and project is usually more cost-effective than a separate trip.
Ready to get a real number on a whole house generator?
We come to your home, run the load calc, confirm your gas service, check permit requirements, and give you a written all-in price. No obligation, no sales pitch. Most walk-throughs take 30 minutes.
Whole House Generator FAQs for Long Island Homeowners
It depends on what you're protecting. If your main concern is keeping the sump pump, refrigerator, and a few lights running during a nor'easter outage, a partial backup generator with load management (11kW to 14kW) handles that for significantly less money than a whole-house system. If you want to run central A/C, a well pump, an electric range, and charge an EV during an outage without managing which circuits are on, a whole-house 22kW or larger unit is the right call. Most Long Island homeowners end up somewhere in between — we help you figure out which side of that line your household falls on.
The honest answer is that you need a load calculation, not a rule of thumb. That said, general guidance for Long Island homes: 11kW to 14kW for essential circuits in homes under 2,000 sq ft; 22kW for whole-house coverage on a colonial or hi-ranch with central A/C; 26kW to 36kW for homes with electric heat pumps, pools, or EV chargers you want to run during outages. We run a free NEC Article 220 load calc on every quote.
Most Nassau County neighborhoods and a large portion of western Suffolk County are served by National Grid gas. If you have a gas furnace, water heater, or stove, you have gas service and can run a standby generator off it. Parts of eastern Suffolk, Fire Island, and some waterfront communities in Nassau don't have natural gas infrastructure — those homes use propane. The easiest way to check is to look at your utility bill. If you pay National Grid for gas, you have the connection.
A standby generator is permanently installed outside your home, connected to your gas line and your electrical panel through an automatic transfer switch. It starts automatically within seconds of an outage, runs as long as needed, and shuts off when PSEG power is restored. A portable generator runs on gasoline, must be started manually and refueled regularly, cannot be run inside or in a garage due to carbon monoxide risk, and must be connected to the house via an extension cord or a manual transfer switch. For Long Island outages that last three to ten days — as Sandy and Ida demonstrated — portable generators are a temporary inconvenience solution. A standby is a permanent home infrastructure upgrade.
The physical installation — concrete pad, gas line, transfer switch, wiring, commissioning — takes one to two days for most residential installs. The full project timeline from signed contract to running generator is typically two to four weeks, accounting for Nassau or Suffolk County permits, PSEG interconnection notification, and equipment delivery. Summer and fall (post-storm season) can run longer due to permit office backlogs.
Nassau County: you need an electrical permit (for the transfer switch and wiring), a gas permit (for the gas line connection), and usually a building permit for the concrete pad and setback compliance. Incorporated Nassau villages — Garden City, Hempstead, Freeport, Long Beach, and others — have their own building departments with separate permit processes. Unincorporated Nassau areas (Levittown, East Meadow, Massapequa, etc.) go through Nassau County Buildings. Suffolk County: permits are handled at the town level — Babylon, Brookhaven, Huntington, Smithtown, Islip, etc. each have their own building department. Requirements are similar to Nassau. We handle permits in both counties as part of every installation.