What Size Generator for a House

Choosing what size generator for a house is not just about convenience—it’s about safety, performance, and ensuring your home stays functional during power outages. Whether it’s a storm, a blackout, or just unreliable grid supply, having the right generator can make all the difference. But how do you know what size is right?

To answer that, you need to consider the appliances you’ll power, how long you’ll need backup, and your home’s total electrical demand. Let’s explore this topic step-by-step in a simple, easy-to-read way. By the end of this guide, you’ll understand generator sizing better and feel confident about your choice.

Why Knowing What Size Generator for a House Matters

A generator that is too small will overload and shut down. One that is too big will waste fuel and cost more. The goal is to match the generator capacity with your power needs.

Power is measured in watts. Appliances have running watts and starting watts. Starting watts are often higher because of the surge when the appliance first turns on.

So, what size generator for a house depends on the total wattage of appliances you plan to use. This includes your refrigerator, lights, fans, HVAC system, well pumps, computers, and more.

How to Estimate What Size Generator for a House

Let’s look at a table to understand common appliance wattages.

To size your generator, add up the starting watts of the appliances you want to run simultaneously.

For example, if you plan to power a refrigerator, lights, a microwave, and a sump pump, you’ll need around:

• 2200 (fridge)
• 2150 (sump pump)
• 1000 (microwave)
• 100 (lights)

Total: 5450 watts

That means you need at least a 6000-watt generator, or 6 kW. Always add a buffer of 10–20% to be safe.

Whole House vs Essential Circuits: What Size Generator for a House?

There are two approaches: whole house backup or essential circuit backup.

• Whole house backup means powering everything, including HVAC and large appliances. You may need a 15kW to 25kW generator depending on house size.
• Essential circuit backup powers only critical systems—like lights, fridge, and sump pump. For this, 5kW to 8kW might be enough.

Knowing your choice helps determine what size generator for a house fits your needs.

Using a Generator Wattage Estimator

You can use a Generator Wattage Estimator to speed up calculations. These tools ask you to select your appliances, and then it automatically adds up the watts.

These are useful when doing initial planning. However, be sure to check actual labels on your home appliances, since real wattage varies by model.

Using a Generator Sizing Calculator

There are many free Generator Sizing Calculator tools online. You just input the type of building, power phase (single or three-phase), and expected load in watts or amps. It calculates the generator size in kW and kVA.

For residential use, it usually recommends between 6 kW and 20 kW. Some tools include specialized calculators like:

• Backup Generator Sizing Calculator
• Generator Sizing Calculator for Pumps

These are very helpful when including water pumps, HVAC systems, or backup power for home-based equipment like aquariums or home labs.

Example Load Calculation: What Size Generator for a 3-Bedroom House?

Say you live in a standard 3-bedroom house with the following running at the same time:

• Refrigerator (700W)
• 1 Ton Split AC (1200W)
• Lights and fans (500W)
• Laptop and TV (300W)
• Water pump (1000W starting, 400W running)
• Microwave (1000W)

Total running watts = 4100W
Total starting watts = 6100W

In this case, a 7 kW generator is recommended. It will cover both running and starting loads.

Generator Circuit Breaker Sizing

When sizing the generator, don’t forget about the Generator Circuit Breaker Sizing. This protects the generator and the house wiring. The circuit breaker size depends on the generator’s full load current.

To calculate it:

Breaker Size (A) = Generator kW × 1000 / Voltage

For example, for a 7 kW generator at 240V:

Breaker Size = (7000 ÷ 240) = 29.17A
Use a 30A breaker

This step is vital for safety and code compliance.

Fuel Types and Runtime: Diesel, Gasoline, Propane

When thinking about what size generator for a house, also consider the fuel type.

• Gasoline is easy to find but not ideal for long-term storage.
• Propane burns cleaner and stores longer.
• Diesel is fuel-efficient and durable for larger generators.

Fuel efficiency affects how long your generator can run per tank. For instance, a 7 kW gasoline generator might run 8 hours on 5 gallons.

If outages last longer, you may want a larger fuel tank or automatic refueling system.

Portable vs Standby: Which Affects Size?

A portable generator is usually under 10 kW. These are suitable for essential circuits and are manually operated.

A standby generator is installed permanently and starts automatically. These can range from 10 kW to 25 kW for residential use.

So if you’re wondering what size generator for a house with automation, a standby unit around 15–20 kW may be best.

Tips for Accurate Sizing

• Always use real wattage labels on devices
• Include a 15% buffer above total wattage
• Factor in starting watts of inductive loads like pumps and ACs
• Use tools like the Generator Sizing for UPS Systems to determine battery backup and transition time

Maintenance and Load Testing

Once you’ve selected the right size, keep your generator maintained. Run monthly load tests to ensure it handles your home load without issues.

You can use a Generator Sizing Calculator during maintenance to verify load performance against initial specs. It’s also useful when adding new appliances to your home.

Conclusion: Final Thoughts on What Size Generator for a House

Now you know how to answer the big question—what size generator for a house. It all comes down to your home’s power needs, the devices you want to run, and how long you want backup for.

A safe estimate for most homes lies between 7 kW and 20 kW. Use tools like the Backup Generator Sizing Calculator, Generator Wattage Estimator, and Generator Circuit Breaker Sizing charts to guide you.

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