What size generator do I need?

A typical refrigerator runs at 280 W and needs about 1,000 W for a moment to start (Champion wattage chart: 150 to 400 W running, 800 to 1,200 W starting). With 20 percent headroom that is 400 running and 1,200 starting watts.

A small inverter or a power station covers this. Look for at least 400 running and 1,200 starting (peak) watts.

Running: 280 + 300 = 580 W. Only the bigger surge counts, the refrigerator's 720 W, so the starting total is 1,300 W. With headroom: 700 running and 1,600 starting watts.

A small inverter or a power station covers this. Look for at least 700 running and 1,600 starting (peak) watts.

A 1/3 hp sump pump typically runs at 650 W and starts at 1,300 W (Champion wattage chart). With headroom: 800 running and 1,600 starting watts. It is a motor, so the starting figure is the one to check.

A small inverter or a power station covers this. Look for at least 800 running and 1,600 starting (peak) watts.

A 1 hp well pump typically runs at 1,500 W and starts at 3,000 W (Champion wattage chart). With headroom that is 1,800 running and 3,600 starting watts, more peak than the small inverters we verified (2,200 to 2,350 W). Most submersible well pumps run on 230 V (Oakville Water Services), so look for a generator with a 240 V outlet.

The small inverters we verified do not cover that 3,600 W start, so go one size up: the WEN DF475T (3,800 running, 4,750 peak watts) covers both numbers. Look for at least 1,800 running and 3,600 starting (peak) watts.

A gas furnace's 1/2 hp blower typically runs at 550 W and starts at 1,200 W (Champion wattage chart). With headroom: 700 running and 1,500 starting watts. Champion recommends a low distortion inverter (under 3 percent THD) for high efficiency furnace control boards; ask your furnace maker.

A small inverter or a power station covers this. Look for at least 700 running and 1,500 starting (peak) watts.

Running: 280 + 550 = 830 W. The bigger surge is the refrigerator's 720 W, so the starting total is 1,550 W. With headroom: 1,000 running and 1,900 starting watts.

A small inverter generator covers this. Look for at least 1,000 running and 1,900 starting (peak) watts.

Champion lists a 3 ton unit at 3,000 to 3,500 W running and 5,000 to 6,000 W starting; the typical figures are 3,250 and 5,500. On its own that needs 3,900 running and 6,600 starting watts. Generac says a 3 ton unit can demand 15 to 18 kW to start, so read the condenser's data tag (locked rotor amps) and ask an electrician about a soft starter.

The mid-size inverters we verified do not cover that 6,600 W start, so go one size up: the WEN DF680iX (5,100 running, 6,800 peak watts) covers both numbers. Look for at least 3,900 running and 6,600 starting (peak) watts.

Typical figures: 1,050 W running and 2,100 W starting (Champion wattage chart: 900 to 1,200 W running, 1,800 to 2,400 W starting). With headroom: 1,300 running and 2,600 starting watts.

The small inverters we verified do not cover that 2,600 W start, so go one size up: the Champion 4000-Watt RV Ready Inverter (3,000 running, 4,000 peak watts) covers both numbers. Look for at least 1,300 running and 2,600 starting (peak) watts.

Champion wattage chart lists 750 to 1,500 W with no starting surge; the typical figure is 1,130 W. With headroom: 1,400 watts. Check the label: a heater on high can sit at the top of that range.

A small inverter generator covers this. Look for at least 1,400 running and 1,400 starting (peak) watts.

Typical figures: 1,750 W running and 3,150 W starting (Champion wattage chart: 1,500 to 2,000 W running, 2,800 to 3,500 W starting). On its own that needs 2,100 running and 3,800 starting watts: the start, not the running draw, sets the size.

The small inverters we verified do not cover that 3,800 W start, so go one size up: the Champion 4000-Watt RV Ready Inverter (3,000 running, 4,000 peak watts) covers both numbers. Look for at least 2,100 running and 3,800 starting (peak) watts.

A 7-1/4 in circular saw, a 1/2 in drill, a 1 hp air compressor, an LED work light and a heavy duty battery charger run at 5,270 W together. The 1 hp air compressor's 3,000 W surge is the biggest, so the starting total is 8,270 W; with headroom you need 6,400 running and 10,000 starting watts.

The mid-size portables we verified do not cover that 10,000 W start, so go one size up: the Westinghouse WGen9500DFc (9,500 running, 12,500 peak watts) covers both numbers. Look for at least 6,400 running and 10,000 starting (peak) watts.

Add the running watts of everything you want on at the same time, add the single largest starting surge, then add 20 percent headroom. Our outage essentials list (a refrigerator, a furnace blower, a sump pump, six LED bulbs, a router, three phone chargers and a microwave) comes to 4,200 starting and 3,300 running watts, which a mid-size inverter or portable covers.

Size it from what you will run at once, not from the size of the house. Our outage essentials list needs 3,300 running and 4,200 starting watts, which the WEN DF475T (3,800 running, 4,750 peak watts) covers. Add a 3 ton central air conditioner and the same list needs 7,200 running and 9,900 starting watts, which takes a large portable such as the Westinghouse WGen9500DFc (9,500 running, 12,500 peak watts).

Briggs and Stratton says the essential items in a typical home average 5,000 to 7,000 running watts (5 to 7 kW). Champion says most 2,000 sq ft homes need a 5,000 to 7,500 watt generator for the essentials, and 10,000 watts or more to run central air. Running everything at once usually means a home standby unit sized by an electrician's load calculation; see whole house sizing.

Generac says to size a generator to the loads you want to run, not to square footage alone. Its own example puts a 1,550 sq ft home at a 10 to 14 kW standby unit with load managers, and 18 kW with a heat pump or high-draw medical equipment. For the essentials only, our outage list needs 3,300 running and 4,200 starting watts whatever the size of the house.

Champion says most 2,000 sq ft homes need a 5,000 to 7,500 watt generator to cover the essentials, and 10,000 watts or more to run central air. For a home standby unit, Generac sizes a 2,000 sq ft home at 18 to 22 kW. See whole house sizing.

Generac's FAQ calls a 22 kW standby unit the industry standard for whole-home protection in houses of 2,500 to 3,000 sq ft, though the same page sizes a 2,000 sq ft home at 18 to 22 kW. Treat it as a starting point: Generac also asks for a professional load analysis before you buy.

The size a licensed electrician's load calculation gives for the loads you want on. Generac asks for a professional load analysis, and its load managers pause lower-priority loads so a smaller unit can cope. Champion's standby range runs from 8,500 to 26,000 watts and up. Our whole house list with gas heat needs about 14,900 running and 20,300 starting watts, which lands in the 16 to 22 kW standby range.

Running (rated) watts are what an item draws while it runs. Starting watts are the extra burst a motor needs for two to three seconds to start, according to Briggs and Stratton. Heaters, toasters and bulbs have no starting surge; refrigerators, pumps, air conditioners and power tools do.

In most cases only one item starts or cycles at the same moment, so Briggs and Stratton, Champion, Generac, Cummins and Westinghouse all add only the largest surge to the running total instead of every surge.

A Cummins dealer article advises adding 20 to 25 percent to your total; we use 20 percent and say so. Both of the generator's numbers must clear your totals: its rated (running) watts and its peak (starting) watts.

Usually, yes. The typical refrigerator in our chart runs at 280 W and starts at 1,000 W, so the calculator asks for 400 running and 1,200 starting watts. The Honda EU2200i we list is rated 1,800 W running and 2,200 W peak. Check your refrigerator's label; some list higher figures.

If 5,000 W is its running rating, it covers the outage essentials list (3,300 running and 4,200 starting watts with headroom), but not the essentials plus a 3 ton central air conditioner, which needs 7,200 running and 9,900 starting watts. Listings often lead with the peak figure, so check which number the 5,000 is.

Sometimes. Champion lists a 3 ton central air conditioner at 3,000 to 3,500 running and 5,000 to 6,000 starting watts, but Generac says a 3 ton unit can demand 15 to 18 kW to start. Read the locked rotor amps on the condenser's data tag (Cummins), and ask about a soft starter, which Generac says cuts startup draw by up to 70 percent.

Outside only, at least 20 feet from the house, with the exhaust pointed away from doors and windows (CPSC). Never in a garage, basement, crawlspace, shed, porch or carport, even with the doors open. Put battery-backed CO alarms on every level of the home.

No. Plugging a generator into any wall outlet, including a dryer outlet, is backfeeding. CPSC says it puts utility workers and neighbors at risk of electrocution. Connecting to house wiring takes a transfer switch or an approved interlock installed by a licensed electrician.

Yes. Champion says propane typically delivers about 10 percent less wattage than gasoline, and natural gas 10 to 15 percent less. Size against the generator's propane figure if that is the fuel you will use; the dual fuel picks list both.

Honda, Champion and Westinghouse manuals say output drops about 3.5 percent for every 1,000 feet. Tick "I am above 3,000 ft" in the calculator and it adds 10 percent to the need.

A 30 amp shore cord is 120 V, so the RV can draw at most 3,600 watts (Cummins). Our 30 amp preset (a 13,500 BTU air conditioner, refrigerator, microwave, four LED bulbs, a TV and two chargers) adds up to 3,470 running watts. With the air conditioner's start and 20 percent headroom, the calculator asks for 4,200 running and 5,900 starting watts. Look for a TT-30R outlet.

For small loads, often. Consumer Reports says power stations are the only type of generator that can be used indoors safely, and the 1 kWh and larger units we list have the surge for a typical refrigerator. Consumer Reports also says they will not run a well pump (Jackery says its Explorer 1000 Plus can run a 900 W well pump for about 1.2 hours), and once the battery is empty you need sun or grid power to recharge it. Our power station picks by capacity show which sizes cover which loads.