Generators

A generator is the fastest path to restoring critical power during an outage, but most people who own one haven't thought through the connection method, fuel supply, or runtime requirements until they're already in the dark. A 3,500-watt portable unit sitting in a garage without a transfer switch and a half-empty gas can protects almost nothing. Getting the setup right in advance means the difference between riding out a three-day outage comfortably and scrambling through it.

Generator types

Four categories cover most preparedness and off-grid needs. Each involves real tradeoffs between portability, fuel efficiency, noise, power quality, and upfront cost.

Type	Typical output	total harmonic distortion (THD)	Noise
Conventional portable	3,500–10,000 W	15–25%	65–75 dB
Inverter portable	1,000–7,000 W	<3%	50–60 dB
Dual-fuel portable	3,000–8,000 W	Varies	65–75 dB
Standby (propane/NG)	7,000–22,000 W	<5%	62–68 dB

Type	Fuel tank	Best use
Conventional portable	4–7 gal (15–26 L)	Tools, pumps, resistive heating
Inverter portable	1–4 gal (4–15 L)	Electronics, CPAP, battery chargers
Dual-fuel portable	4–6 gal (15–23 L)	Fuel flexibility during shortages
Standby (propane/NG)	Inline supply	Whole-home automatic backup

Conventional generators run at a fixed 3,600 RPM regardless of load. They produce "dirty power" — voltage and frequency fluctuations with total harmonic distortion (THD) typically 15–25%. That level of distortion can damage microprocessors, CPAP machines, variable-speed motors, and battery chargers. Use them for loads that tolerate rough power: well pumps, shop tools, resistive space heaters, and incandescent or LED lighting.

Inverter generators throttle engine speed to match the load, then electronically synthesize a clean sine wave. THD below 3% is safe for any sensitive electronics. Fuel consumption drops 20–40% at partial load compared to a conventional generator of equivalent rated wattage. The tradeoff is cost — inverter generators typically run roughly twice the price per rated watt of conventional units.

Standby generators start automatically within seconds of a grid outage via an automatic transfer switch (ATS). They are hardwired to the home electrical panel and run on propane or natural gas from a fixed supply, eliminating the fuel rotation problem entirely. Installed cost including the unit, ATS, and electrician labor is a significant investment.

Field note

For most households, the practical sweet spot is a 3,500–5,000W inverter generator paired with a manual interlock kit on the main panel. This combination handles critical loads, protects sensitive electronics, and costs far less than a standby system while remaining portable enough to store securely between uses.

Sizing your generator

Undersizing causes overload trips and frustration. Oversizing wastes fuel and increases operating cost. The correct approach starts with a load audit, not a watt count.

Step 1 — List critical loads and their surge (starting) watts.

Most motor-driven appliances draw 2–3 times their running wattage for 1–3 seconds at startup. This surge is what overloads generators, not the sustained running load.

Appliance	Running watts	Surge watts
Refrigerator (mid-size)	150–400 W	800–1,200 W
Chest freezer	100–300 W	600–900 W
Well pump (1/2 HP / 0.37 kW)	1,000 W	2,500 W
Sump pump (1/3 HP / 0.25 kW)	800 W	2,000 W
Window AC (10,000 BTU)	1,200 W	3,600 W
CPAP (no heat humidifier)	30–60 W	60–120 W
LED lighting (10 fixtures)	80 W	80 W
Phone and laptop charging	100 W	100 W

Step 2 — Calculate total simultaneous running load.

Add only the appliances you plan to run at the same time. A typical critical-load setup — refrigerator, freezer, lights, and communications charging — totals roughly 700–1,000 W running.

Step 3 — Identify the largest single surge load.

This is almost always a well pump, sump pump, or air conditioner. Add that surge wattage to your running total: your generator must handle both at the same instant.

Step 4 — Add 20% headroom.

Generators run most reliably at 50–80% of rated capacity. Running at 100% for extended periods stresses the engine and accelerates wear.

Example: 900 W running load + 2,500 W well pump surge = 3,400 W peak. Adding 20% headroom: you need a generator rated at minimum 4,080 W. A 4,000–5,000 W unit covers this load profile cleanly.

For whole-home coverage including central air conditioning, budget for 10,000–18,000 W — that's standby territory, not portable generator territory.

Fuel comparison

Fuel	Shelf life	Generator availability	Energy density	Notes
Gasoline	3–6 months untreated; up to 2 years stabilized	Widest selection	32 MJ/L	Ethanol blends phase-separate; treat with Sta-Bil
Propane	Indefinite (sealed cylinder)	Good	25 MJ/L	Clean-burning; 5–10% power reduction vs gasoline
Diesel	12–24 months treated	Large conventional units	35 MJ/L	Highest energy density; harder cold start
Natural gas	Indefinite (piped)	Standby only	Grid-supplied	Fails if gas main is disrupted

A 3,000W conventional generator running at 50% load consumes approximately 0.25 gallons (0.95 L) of gasoline per hour. At full load, that rises to 0.4–0.5 gallons (1.5–1.9 L) per hour. For a 72-hour outage running 8 hours per day, budget approximately 6–10 gallons (23–38 L) of treated gasoline.

Propane is the most storage-stable option for portable generators. Conversion kits are available for most major gasoline generators for a moderate investment. Propane produces fewer engine deposits and stores indefinitely in sealed cylinders — the tradeoff is a 5–10% reduction in peak power output compared to the same engine on gasoline.

For container selection, treatment products, and rotation strategy, see fuel storage.

Transfer switch options

Connecting a generator to your home wiring safely requires one of three methods. Running extension cords directly from the generator to individual appliances is safe but inconvenient for whole-house use; the following options feed your electrical panel instead.

Never backfeed the grid

Plugging a generator into a wall outlet using a "male-to-male" extension cord backfeeds power into the grid. Utility workers working on what they believe are de-energized lines can be electrocuted. This has killed people. It is also a code violation. Always use a proper transfer switch or interlock device — no exceptions.

Manual transfer switch (MTS): A separate subpanel hardwired to the main panel with a physical lever that disconnects grid power and connects generator power. Installation requires a licensed electrician. The subpanel covers only the circuits you choose to back up. Installed cost is affordable to moderate investment including labor.

Interlock kit: A mechanical plate bolted to your existing main panel that prevents the main breaker and generator input breaker from being energized simultaneously. It uses the existing panel's breaker slots — you choose which circuits receive power by switching individual breakers. Compatible kits exist for most major panel brands. Installed cost is affordable to moderate investment depending on panel model and local labor rates. The lowest-cost compliant option.

Automatic transfer switch (ATS): Detects grid failure and transfers loads automatically without human intervention. Required for standby generators. Installed cost for the ATS alone is a moderate to significant investment, separate from generator and wiring costs. Not practical for portable generators, which require manual start and a warm-up period before accepting load.

Carbon monoxide safety

CO kills in minutes — distance is not optional

Carbon monoxide is colorless, odorless, and accumulates silently. OSHA's permissible exposure limit is 50 ppm as an 8-hour time-weighted average. At 200 ppm, headache and dizziness develop within 2–3 hours. At 800 ppm, death can occur within 2–3 hours. At 1,600 ppm, death can occur within 2 hours. A running generator near a building can push indoor CO concentrations above 1,000 ppm within minutes. The CDC attributes more than 400 non-fire CO deaths per year in the U.S. to portable generators — more than any other single consumer product. Never operate a generator inside a garage, basement, or carport, even with the door or window open.

Follow these requirements whenever a generator is running:

Position the generator at minimum 20 feet (6 m) from all doors, windows, and vents
Orient the exhaust outlet away from the structure and away from prevailing wind direction
Install battery-operated CO detectors on every level of the home, including sleeping areas
Test CO detectors before each storm and outage season — not when the alarm triggers

Load management

A generator that runs all loads simultaneously burns more fuel and works harder than necessary. A load management plan operates the generator at 50–70% of rated capacity, extends fuel runtime, and extends engine service life.

Tier your loads by priority:

Always on during generator runtime: refrigerator, freezer, medical equipment (CPAP, oxygen concentrator), essential lighting, communications charging
Scheduled intervals: well pump (run during generator windows, pressure tank buffers demand between cycles), washing machine, EV charging
Suspend entirely: electric water heater, electric range or oven, electric clothes dryer, central air conditioning (substitute fuel-based heating and cooling where possible)

Cycle motor loads strategically. A pressure-tank well pump doesn't need to run continuously — it runs in short bursts when tank pressure drops below the cut-in point. Design your power schedule around this reality: run the generator to recharge the battery bank and cycle the well pump, then suspend generator operation for several hours while the battery bank handles ongoing small loads.

Pairing a generator with a battery bank and inverter system allows the battery to absorb motor surge loads without straining the generator, smooths power quality for sensitive electronics, and allows the generator to operate in efficient high-load charging cycles rather than idling at 10–15% of rated capacity.

Maintenance schedule

A generator that hasn't run in two years under load is likely to fail on the first pull when you actually need it. The carburetor, spark plug, oil, and fuel system all degrade during storage. The underlying repair skills — carburetor cleaning, ignition diagnosis, fuel system service — are covered in small engine maintenance.

Before every use:

Check oil level; add if below the full mark on the dipstick
Verify fuel is fresh (under 30 days old) or treated with stabilizer
Start and warm up 2–3 minutes before connecting any load

Monthly:

Run under at least 500–1,000 W of resistive load for 30 minutes
Check the air filter; clean or replace if visibly dirty
Verify fuel shut-off valve opens and closes freely

Annual (or every 100 operating hours, whichever comes first):

Change engine oil — most small generators use 10W-30; check manufacturer spec for synthetic compatibility
Replace the spark plug and verify gap matches specification (typically 0.028–0.031 in / 0.71–0.79 mm)
Replace the air filter and fuel filter
Drain the carburetor bowl if storing with ethanol-blend gasoline; ethanol leaves gum deposits that clog the main jet and pilot circuit
Clean the exhaust outlet; carbon buildup restricts flow and causes backpressure

Field note

Store a pre-labeled kit beside the generator: the correct oil (1 quart), spare spark plug at the correct gap, and a laminated card showing your critical-load calculation and which breakers to switch. You will not remember these details under stress at 2 a.m. during an ice storm.

Practical checklist

With your generator sized and safely connected, the next layer is inverter and battery integration to smooth power quality and reduce fuel burn — particularly for overnight critical loads and sensitive electronics. For extended outage planning where generator fuel becomes the constraint, off-grid solar and battery storage provides the recharge path that doesn't depend on a fuel supply chain.