Last verified: October 1, 2026
For home backup, the right portable generator is one that can start your biggest motor, connect safely to your panel and shut itself off if carbon monoxide builds up. For most houses that means a 5,000–9,500 running-watt model with a 240-volt outlet, electric start and automatic CO shut-off, ideally dual fuel. Brand matters less than getting these features right.
The features that matter for home backup
- Running and starting watts. They must cover your essentials and your biggest start-up surge. Use our calculator; most homes end up needing 5,000–9,500 running watts.
- A 240 V outlet. You need it to feed your panel through an interlock or transfer switch, and to run a 240 V well pump. Look for a 30 A (L14-30) or 50 A (14-50) outlet that matches your inlet box.
- Automatic CO shut-off. It turns the engine off if carbon monoxide builds up around it. Look for models certified to ANSI/PGMA G300 or UL 2201.
- Dual fuel. Propane stores for years without going stale and is easier to keep on hand than gasoline, but output is lower on propane, so check both ratings.
- Electric start. Push-button or remote start means anyone in the household can start it in a storm, as long as the battery is kept charged.
- Run time. Longer runtime at 50% load means fewer refueling trips in the night.
- Inverter technology. Quieter, more fuel-efficient and clean power for electronics. Ideal for smaller loads; large inverter units cost noticeably more.
Which size class fits your house?
Portable generators fall into three broad bands. Models of 2,000–3,500 W, often inverters, handle the fridge, lights, phones, internet or a CPAP through extension cords, and usually have no 240 V outlet. At 5,000–7,500 W, you can run the essentials through an interlock: fridge, sump pump, furnace blower, lights and some outlets. From 8,000–9,500 W and up, you can add a 1 HP well pump, a microwave and more, sometimes even a small AC fitted with a soft starter.
See the worked examples in What Size Generator Do I Need? and Generator Size for a Well Pump and Sump Pump.
Inverter or conventional?
- Inverter generators adjust engine speed to the load, so they are quieter and use less fuel at light loads. Their power is very stable, good for electronics. Large inverter models are expensive.
- Conventional (open-frame) generators deliver more watts per dollar and are the usual choice for 7,000+ W home backup. Modern appliances generally run fine on them.
Budget for the whole setup, not just the generator
- Generator: typically $500–$2,500 (HomeGuide).
- Interlock kit or manual transfer switch, installed: $400–$1,300 (HomeGuide).
- Inlet box ($20–$100) and a heavy-duty generator cord long enough to keep the generator more than 20 feet from the house.
- Battery-operated CO alarms for every level of the home.
- Fuel cans or propane cylinders, fuel stabilizer, spare oil.
Before you buy: a short checklist
- Have you calculated your running and starting watts?
- Does the outlet match the inlet box your electrician will install?
- Does it have automatic CO shut-off?
- Can it run on propane if gasoline is scarce after a storm?
- Where will it sit during an outage, and is that spot more than 20 feet from windows and doors?
- Is there a local service center for the brand?
Three example setups
A city townhouse with short outages that only needs the fridge, lights, internet and phone charging is well served by a quiet 2,000–3,500 W inverter and extension cords. A suburban house with a basement, which adds a sump pump, the furnace blower and a TV, needs 5,000–7,500 W, ideally dual fuel, connected through an interlock kit and a 30 A inlet box. A rural house on a well adds a 1 HP 240 V well pump and a microwave to that list, which calls for 8,000–9,500 W or more with a 240 V outlet, connected through an interlock kit or transfer switch and a 30 or 50 A inlet.
Running loads for the second and third examples are about 3,225 W and 6,225 W, with peaks of about 4,725 W and 8,225 W, using the typical wattages in our sizing guide.
Matching the outlet to your inlet box
Most home connections use one of two outlets on the generator:
- 30 A, 240 V twist-lock (L14-30): the most common for mid-size portables; good for essential circuits.
- 50 A, 240 V (14-50): found on larger generators; allows more power through the inlet.
The inlet box your electrician installs, and the cord between generator and inlet, must match the generator’s outlet. Decide on the generator first, then have the inlet and cord sized to it.
How much fuel to keep on hand
A simple rule: keep enough fuel for at least the first 24–48 hours of an outage, since stations may be closed or have long lines. Check your generator’s runtime at 50% load on its spec sheet, and multiply. With dual fuel, propane cylinders can be stored for years outdoors; gasoline needs stabilizer and rotation. See Dual Fuel vs Tri-Fuel.
Mistakes to avoid when buying
- Buying on peak (starting) watts alone and discovering the running watts are too low for a well pump.
- Choosing a model without a 240 V outlet when you need to power the panel or a 240 V pump.
- Skipping the interlock or transfer switch and planning to “use cords for now”, which often leads to unsafe shortcuts.
- Ignoring noise and CO shut-off features.
- Not checking where you’ll run it more than 20 feet from the house.
Frequently asked questions
Do I need a transfer switch for a portable generator?
Only if you want to power circuits wired into the house (furnace, well pump, hardwired lights). For a fridge and a few lamps, outdoor-rated extension cords are enough. Never connect through a wall outlet. See Why Backfeeding Is Dangerous.
How big a portable do I need for a fridge and freezer?
About 1,200 W running and a little over 3,000 W at start-up covers a typical fridge and freezer with typical wattages, but add lights, internet and phone charging and a 3,500 W inverter is a comfortable choice.
Portable or standby after all?
If you’d rather not refuel every few hours or be home to start it, compare the costs in Standby vs Portable Generator. Safety rules for running a portable are in Generator Carbon Monoxide Safety.