Generators and backup power

Your fridge runs on 200 watts. Starting it needs 1,200.

That gap is why so many backup generators disappoint. A generator is not sized by what your appliances use. It is sized by what they demand in the half second they switch on. Watt Ridge exists to get that math right before you spend the money.

Start with your situation

01

Home backup

The power is out. You want the fridge cold, the furnace running, and the sump pump working before the basement notices.

Size a home generator

02

Mobile and off grid

You need quiet power at a campsite, in a camper, or on a build with no hookups. Noise matters here as much as watts.

Power a camper

03

Vehicle and 12V

You want a real mains outlet in your vehicle, or a battery that stops dying on you every cold morning.

Choose a car inverter

How many watts do you actually need?

Most people guess high and pay for fuel they never burn. Or they guess low, and the generator stalls the first time the well pump kicks in. Three sizes cover almost every home in the country. Find yours, then read the guide that goes with it.

Essentials only

3,000 to 5,000 W

5,000 W

Keeps a fridge, a chest freezer, your lights, the router, and a sump pump alive. One small window air conditioner fits if nothing else is starting at the same moment. For a two day outage, this is the size most families genuinely need.

Essentials plus heat and water

7,000 to 10,000 W

10,000 W

Adds the two that catch people out: a furnace blower and a well pump. Both sip power while running and spike hard on startup. At this size you can feed eight to ten circuits through a manual transfer switch and live close to normally.

Whole house

14,000 to 24,000 W

24,000 W

Central air conditioning, an electric range, and the rest of the panel, all at once. This is standby territory. The unit sits outside on a pad, runs on natural gas or propane, and switches over on its own. It also needs a licensed electrician and a permit.

Bars shown against a 25,000 watt scale. Ranges are typical residential sizing and vary with your appliance mix.

A quick example

Say you buy a 3,500 watt generator. You plug in the fridge (200 W running) and a half horsepower well pump (1,000 W running). That is 1,200 watts. Comfortable. Then the pump cycles and asks for around 2,100 watts for a moment. You are at 2,300 watts and still fine.

Now add a 1,500 watt space heater because the house is cold. The next time that pump starts, you need roughly 3,800 watts. The breaker trips and the lights go out again. Nothing was faulty. The math was just done in the wrong order.

Read the whole house guide
Compare portable sizes

Start with the guide that matches your house

Each guide opens with the load math, not a product list. The gauge below each title shows the typical generator size that guide is written around.

01

Best generator for a whole house

Typical size covered

0 · 6 · 12 · 18 · 25 kW

14 to 24 kW

For homes that want central air and the full panel covered. It walks through automatic standby units, natural gas versus propane supply, and why the transfer switch is not an optional extra.

02

Best portable generator for home backup

Typical size covered

0 · 6 · 12 · 18 · 25 kW

5 to 9 kW

The practical middle, and where most readers land. Enough for the furnace, the well pump, and the kitchen, with no concrete pad, no permit, and no gas line to run.

03

Best portable generator for a camper

Typical size covered

0 · 6 · 12 · 18 · 25 kW

2 to 3.5 kW

Quiet counts for more than raw output here. Inverter units in this band usually run around 48 to 60 dBA, and will normally handle a 13,500 BTU RV air conditioner once a soft start is fitted.

Safety

The outage is not the dangerous part

Generators are simple machines with one serious hazard each. None of these are rare. All of them are avoidable with about ten minutes of planning, done before the storm arrives rather than during it.

Carbon monoxide

A portable generator puts carbon monoxide into its exhaust, and you cannot smell it or see it. Run it outdoors only, at least 20 feet from the house, with the exhaust pointed away from doors, windows, and vents. Never in a garage, a shed, or under a covered porch, even with the door wide open. The US Consumer Product Safety Commission links portable generators to roughly 85 carbon monoxide deaths a year.

Read the placement rules

Backfeeding

Plugging a generator into a wall socket to power the house is called backfeeding. It pushes electricity back out onto the utility line and can kill a line worker who believes that circuit is dead. It can also destroy your generator when the grid returns. Use a transfer switch or an interlock kit, fitted by a licensed electrician. There is no safe shortcut on this one.

See setup and install guides

Fuel storage

Gasoline vapour is heavier than air, so it sinks and travels along the floor. Store fuel in approved containers, outside living space, well away from any pilot light, water heater, or furnace. Let the engine cool before you refuel, because fuel spilled onto a hot muffler ignites straight away.

Fuel, safety and how it works

Batteries and charging

AGM batteries are sealed, so you cannot top them up when they lose water. Charge them on an AGM profile, which normally means an absorption voltage around 14.4 to 14.7 volts. A charger left on a flooded setting will overcharge an AGM, dry it out from the inside, and quietly cut years off its life.

Choose an AGM charger

Setup, install and DIY projects

Four sections, four different jobs

The site is split by what you are trying to do, not by product type. Pick the one that matches the question in your head right now.

01

Buying and comparison guides

Sizing first, then a shortlist. Every guide starts with the load you need to carry, never with a list of products looking for a reason.

02

Fuel, safety and how it works

Carbon monoxide, backfeeding, fuel storage, and the plain English version of how these machines turn fuel into usable power.

03

Setup, install and DIY projects

Transfer switches, interlock kits, cable sizing, and a clear line marking where a job stops being DIY and needs an electrician.

04

Reviews

One product at a time. Running watts, starting watts, runtime, noise, and a note on where each figure came from.

Five numbers that decide which generator you buy

Spec sheets are crowded, and most of it does not matter. These five figures do almost all the work. Learn them once and you can read any listing in under a minute.

01

Starting watts, not running watts

Anything with a motor needs a surge of power to get moving. It lasts well under a second, but your generator has to cover it or the breaker trips and everything stops. Look at how wide the gap gets.

Refrigerator

Running

200 W

Starting

1,200 W

Sump pump, one third horsepower

Running

800 W

Starting

1,500 W

Well pump, half horsepower

Running

1,000 W

Starting

2,100 W

Furnace blower, half horsepower

Running

800 W

Starting

2,350 W

Bars shown against a 2,400 watt scale. Figures are typical values for common household equipment and vary by model and age.

Quick tip

Write down the running watts and the starting watts for everything you want to keep alive. Add all the running watts together. Then add only the single largest starting watt figure on the list. Motors almost never start at the same instant, so that one rule stops you buying two sizes bigger than you need.

02

Noise is measured at 23 feet

Generator noise is quoted from 23 feet away, not from where you are standing. Inverter models usually sit between 48 and 60 dBA. Conventional open frame portables run closer to 65 to 75 dBA. That looks like a small gap on paper, but every 10 dBA is roughly twice as loud to your ears. At a campsite it is the difference between being welcome and being asked to move.

03

Runtime is quoted at part load

When a spec sheet promises 11 hours, it almost always means 11 hours at 25 or 50 percent load. Run the same machine close to flat out and you can roughly halve that number. Always check the load percentage printed next to a runtime figure before you compare two generators, because two brands often quote at different loads.

04

Gasoline goes stale, propane does not

Untreated gasoline starts to break down in about three to six months, and stale fuel is the single most common reason a stored generator will not start when you finally need it. Stabiliser buys you longer. Propane never goes stale, which is why dual fuel is popular for backup use, but propane typically gives you around 10 percent less power output than gasoline from the same engine. Size for the fuel you will actually run.

05

Pure sine wave versus modified sine wave

A pure sine wave inverter or inverter generator delivers total harmonic distortion under about 3 percent, which is close to grid power. A modified sine wave unit is usually somewhere between 25 and 40 percent. Simple loads like a kettle or a work light do not care at all. Laptops, CPAP machines, variable speed motors, and some battery chargers absolutely do, and they can run hot, buzz, or refuse to work.

See the car inverter guide

Latest guides and reviews

New research lands here first. Sizing guides, safety explainers, install walkthroughs, and single product reviews.

How Watt Ridge gets its numbers

Every figure on this site comes from three places. Manufacturer specifications and owner manuals. Published standards and public safety guidance from bodies like the CPSC. And verified owner reviews from people who live with the machine year round.

Watt Ridge does not run hands on tests, and will never pretend otherwise. That honesty is the point. A spec sheet tells you what a generator can do on a test bench on a good day. Owner reports tell you what it does after eighteen months in a damp garage. Both are useful, and quietly mixing them together is how bad advice gets made.

  • Manufacturer claims are labelled as manufacturer claims.
  • Owner reported problems are labelled as owner reported.
  • Estimates are labelled as estimates, with the assumption shown.
  • Where a job legally needs a licensed electrician, the guide says so and stops.

    • Watt Ridge is a participant in the Amazon Services LLC Associates Program. If you buy through a link on this site, we may earn a commission at no extra cost to you.

Not sure where to begin? Start with the watts, and everything else gets easier.

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