how many watts to run a house

This is the question I get asked more than any other. And the reason everyone asks is because nobody gives a straight answer. Search for it and you get vague ranges, contradictory charts, and advice from people who clearly haven't tried to run a house on a generator in August.

The answer depends on what you mean by "run a house." There's a massive difference between keeping your food cold and your pipes from freezing versus pretending the grid never went down. And that difference is measured in both watts and dollars.

I'm going to give you the real numbers. Not estimates from a manufacturer trying to sell you a bigger unit. Not rounded averages that don't account for your specific situation. I'll show you how to figure out your exact number, down to the watt, with tools you can buy at any hardware store.

Now let me explain where those numbers come from and why yours might be higher or lower than average.

the two ways to think about household wattage

Before we get into appliance tables and measurement tools, you need to understand a distinction that most guides skip over entirely. There are two fundamentally different questions hiding inside "how many watts to run a house," and they have very different answers.

average continuous load

The average American home consumes about 30 kWh per day, according to the EIA. Divide that by 24 hours and you get roughly 1,250 watts on average. That's a real number, but it's almost completely useless for backup power planning.

Why? Because you don't use electricity evenly throughout the day. At 3 AM when everyone's asleep, your house might be drawing 400 watts — just the refrigerator cycling, a few clocks, and the standby power from devices on standby. At 6 PM when you're cooking dinner, running the dishwasher, the AC is blasting, the kids are watching TV, and someone's charging their EV — you might be pulling 18,000 watts.

That average of 1,250 watts covers both extremes. It tells you almost nothing about what your generator or battery system actually needs to handle.

peak simultaneous demand

This is what actually matters for sizing backup power. Peak demand is the maximum wattage your house draws at any given moment — when multiple appliances are running at the same time. This is the number your generator has to be able to deliver without tripping the breaker or shutting down.

For most homes, peak simultaneous demand falls into one of two categories:

• Essentials only: 5,000-7,500 watts. This covers refrigerator, freezer, well pump (if applicable), furnace blower or space heating, sump pump, lights in key rooms, modem and router, and phone chargers. This is what you'd run on a portable generator during an outage when you're managing loads — no AC, no dryer, no electric oven, no electric water heater.
• Whole house: 15,000-25,000 watts. This covers everything above plus central air conditioning (the big one), electric water heater, kitchen appliances running simultaneously, laundry, entertainment systems, and multiple computers. This is "I don't want to know the power is out" territory.

the complete appliance wattage table

Here are real wattage numbers for common household appliances. I've included both running watts (continuous draw during normal operation) and starting watts (the surge when a motor first kicks on). Starting watts matter because your power source has to handle that spike or it shuts down.

These are typical values. Your specific appliances may differ. When in doubt, check the nameplate on the appliance itself — it's usually a sticker on the back or bottom that lists watts, amps, and voltage.

kitchen

heating and cooling

water and plumbing

laundry

lighting and electronics

medical equipment

That's 40+ appliances. Your house won't have all of them running at once. The trick is figuring out which ones overlap during peak demand — and that's what the next two sections help you do.

essentials-only vs. whole-home: the real difference

This is the most important concept in backup power sizing and the one that saves people the most money. Let me lay it out plainly.

the essentials-only profile: 5,000-7,500 watts

An essentials-only setup means you're keeping your house livable and safe, not comfortable. Here's what a typical essentials load looks like with real numbers:

• Refrigerator: 150W running
• Chest freezer: 100W running
• Well pump (1/2 HP): 1,000W running
• Furnace blower: 500W running
• Sump pump: 800W running
• LED lights (4-5 rooms): 200W running
• Modem + router: 30W running
• Phone chargers (x3): 75W running
• Total running: 2,855W

But the well pump startup surge adds 2,000 watts momentarily, and the sump pump could add 1,600 watts on top of that. With a 20% safety margin for voltage variations, altitude, and the appliance you forgot to put on the list, you're landing at 5,500 to 7,500 watts depending on your specific equipment.

This is a $1,000-2,000 portable generator plus a $300-500 transfer switch. Total installed cost under $3,000 for most people.

the whole-home profile: 15,000-25,000 watts

Now add comfort loads to the essentials:

• Everything above: 2,855W running
• Central AC (3-ton): 3,500W running
• Electric water heater: 4,500W running
• Electric range (one burner + oven): 3,500W running
• Washing machine: 500W running
• TV + entertainment: 200W running
• Desktop computer: 300W running
• Additional lights: 150W running
• Total running: 15,505W

Add in starting surges for the AC compressor (1,750W), the well pump kicking on while the AC runs (2,000W), and your safety margin, and you're looking at 20,000-25,000 watts peak demand.

This requires a 22-27kW standby generator. Installed cost: $7,000-15,000.

See the gap? That gap is where your money lives. A $2,500 portable setup versus a $12,000 standby installation. Both are legitimate choices. But they're different choices for different situations, and you should make yours with your eyes open.

how to read your electrical panel

Your electrical panel tells you more about your home's wattage needs than any chart on the internet, because it describes your house, not the average house. Here's how to read it.

Open your panel door. You'll see a main breaker at the top (usually 100, 150, or 200 amps) and rows of individual circuit breakers below it. Each breaker is labeled (or should be — if yours aren't labeled, that's a weekend project worth doing).

what the main breaker tells you

Your main breaker amperage sets the ceiling on what your house can draw simultaneously. A 200-amp panel on a 240-volt system means your house can theoretically draw up to 48,000 watts (200A x 240V). But you will never actually draw that much. Not even close. Your main breaker represents maximum capacity, not typical usage.

That said, main breaker size gives you a rough sense of scale:

• 100-amp panel: Older or smaller home. Typical peak demand 8,000-15,000W. Common in homes built before 1980 or smaller homes without central AC.
• 150-amp panel: Mid-size home. Typical peak demand 12,000-20,000W. Common in homes built 1980-2000.
• 200-amp panel: Modern standard. Typical peak demand 15,000-30,000W. Most homes built after 2000. Required for homes with central AC and electric appliances.

what individual breakers tell you

Each breaker protects a circuit. The breaker amperage tells you the maximum that circuit can handle:

• 15-amp breakers: General lighting and outlets. 1,800W maximum per circuit.
• 20-amp breakers: Kitchen outlets, bathroom outlets, dedicated appliance circuits. 2,400W maximum.
• 30-amp breakers (double-pole): Electric dryer, small AC units. 7,200W maximum at 240V.
• 40-amp breakers (double-pole): Electric range/oven, large AC. 9,600W maximum at 240V.
• 50-amp breakers (double-pole): Electric range, EV charger, sub-panel feed. 12,000W maximum at 240V.

Double-pole breakers (the ones that take up two slots and have their switches tied together) serve 240-volt circuits. These are your big loads: AC compressor, electric water heater, electric range, electric dryer, well pump, EV charger. Add up just the double-pole breakers and you'll see where most of your home's wattage goes.

why 30-amp vs. 50-amp matters

If you're connecting a portable generator to your home through a transfer switch or inlet box, you'll encounter a choice between 30-amp and 50-amp connections. This isn't just a plug shape — it fundamentally limits how many watts you can deliver to your house.

30-amp connection (L14-30 plug)

The standard 30-amp generator outlet delivers 240 volts at up to 30 amps. Maximum power: 7,200 watts. This is what most portable generators in the 5,000-8,000 watt range use. It's enough for an essentials-only setup, but it's a hard ceiling. No matter how big your generator is, a 30-amp connection caps you at 7,200 watts delivered to your panel.

50-amp connection (CS6375 or 14-50 plug)

A 50-amp connection delivers 240 volts at up to 50 amps. Maximum power: 12,000 watts. Generators above 8,000 watts typically use a 50-amp outlet. If you're running a large portable or a small standby unit, a 50-amp connection lets you actually use the generator's full capacity.

the practical impact

I've seen homeowners buy a 12,000-watt generator and wire it to their house through a 30-amp inlet, then wonder why they can only run 7,200 watts before the breaker trips. The connection is the bottleneck. If you have a generator rated above 7,500 watts, make sure your transfer switch, inlet box, and wiring are rated for 50 amps. Otherwise you're paying for watts you can never use.

Standby generators bypass this issue entirely — they connect directly to your panel through an automatic transfer switch that's sized to match the generator. No plugs, no amp limits, no bottleneck.

how to measure your actual wattage with a clamp meter

Tables and estimates are useful. But the most accurate way to know how many watts your house needs is to measure it directly. This is not as intimidating as it sounds.

what you need

A clamp meter (also called a clamp-on ammeter). The Klein CL800 or Fluke 323 are both solid choices in the $50-80 range. You want one that reads AC amps. Most do.

the process

1. Turn off the main breaker. Remove the panel cover (the inner cover, not just the door). You'll see the two main feed wires entering from the top — thick wires, usually black and red, running to the main breaker.
2. Turn the main breaker back on. Yes, the panel is open. Yes, there's exposed wiring. Don't touch anything metal inside the panel with your hands. If this makes you uncomfortable, hire an electrician for this step. There's no shame in that.
3. Clamp around one main feed wire. Open the jaws of your clamp meter and close them around one of the two main wires — just one. Make sure the jaws close completely. Read the amp value on the display.
4. Multiply by 120. That gives you watts on that leg. Repeat for the other main wire. Add both together for your total household draw at that exact moment.
5. Take multiple readings. Measure during your morning routine (shower, coffee, getting ready). Measure in the afternoon when the AC is running. Measure during dinner prep. Measure on a hot day and a mild day. Your highest reading is your peak demand.

what to do with the numbers

Your peak reading is your measured peak demand. Add a 20% safety margin on top of that for startup surges you might not have captured and future loads you might add. That final number is your generator size.

Example: You measure 45 amps on leg one and 38 amps on leg two during peak evening use with the AC running. That's (45 x 120) + (38 x 120) = 5,400 + 4,560 = 9,960 watts. Add 20%: 11,952 watts. A 12kW generator covers you. A 16kW standby gives you room to grow.

seasonal differences: summer vs. winter

Your home's wattage needs are not static. They shift dramatically with the seasons, and this is something most sizing guides either gloss over or ignore entirely.

summer: AC dominates everything

In most of the country, air conditioning is the single largest electrical load in your house from June through September. A 3-ton central AC draws 3,500 watts running with a 5,250-watt startup surge. A 5-ton unit draws 5,000 watts running with a 7,500-watt surge.

During a summer heat wave, your AC runs nearly continuously. That 3,500 watts becomes a constant base load on top of everything else. Summer peak demand can easily reach 20,000+ watts in a typical home.

This is why summer power outages are the most dangerous for your backup system. It's also why "how many watts to run a house" has such a wide range — it depends entirely on whether you're including AC.

winter: heating type determines everything

Winter demand depends almost entirely on your heating system:

• Gas furnace: Only the blower needs electricity — about 500W. Your gas furnace is one of the easiest loads to back up. Winter peak demand with gas heat might be only 5,000-8,000 watts.
• Heat pump: Draws 4,700W running with a 7,000W startup surge. Comparable to AC in terms of electrical demand. When temperatures drop below the heat pump's efficiency range and the auxiliary electric strips kick in, you could be looking at 10,000-15,000W from heating alone.
• Electric furnace: 10,000-20,000W depending on size. This is the worst-case scenario for backup power. An electric furnace can single-handedly require a 25kW generator. If you have one, you need to know about it before you size anything.
• Propane/oil furnace: Similar to gas — only the blower and igniter need electricity. 500-800W. Easy to back up.

the shoulder seasons

Spring and fall are your low-demand periods. No AC, no heat (or minimal), just base loads. This is when your house might run happily on 3,000-5,000 watts. It's also when people test their generators and think "this is easy" — then summer arrives and reality sets in.

putting it all together

Here's the decision framework I use when someone asks me how many watts they need:

1. Define your goal. Essentials only, or whole house? This single decision determines whether you're in the 5,000-7,500W range or the 15,000-25,000W range.
2. List your loads. Use the appliance table above. Write down everything you want to run and add up the running watts.
3. Account for starting surges. Find the appliance with the biggest surge and add that difference to your running total.
4. Add a 20% buffer. For altitude, temperature, aging equipment, and the things you forgot.
5. Verify with a clamp meter. If you want precision — and if you're spending thousands of dollars on a generator, you should want precision — measure your actual peak demand.
6. Match to a generator. The sizing guide maps your watt number to specific generator categories, and the calculator does the math automatically.

If you want to skip straight to generator recommendations, the best whole-home generator guide covers the top standby options. And the sizing hub has everything else related to figuring out what you need before you spend a dime.