What Size Generator for My House?

When the power goes out in the middle of a New Hampshire winter, the question stops being theoretical very quickly. If you're asking what size generator for my house, the right answer depends on what you need to keep running, how your home is heated, and whether you want essential backup or near full-house coverage.

A generator that is too small will force hard choices during an outage. One that is too large can cost more to buy, install, and fuel than you really need. The goal is not to chase the biggest unit on the market. It is to match the generator to your home, your electrical loads, and the way you actually live.

What size generator for my house depends on one main decision

Before anyone talks kilowatts, the first step is deciding what you want backed up. Most homeowners fall into one of two camps.

The first group wants essential circuit coverage. That usually means the heating system, well pump, fridge, freezer, sump pump, some lights, garage door, internet, and a few receptacles. This approach keeps the house safe and functional during an outage without trying to run every major appliance at once.

The second group wants whole-home or near whole-home backup. That often includes central air, electric water heating, kitchen appliances, laundry, and broader lighting and receptacle coverage. This setup offers more comfort and fewer compromises, but it calls for a larger unit and a more careful load calculation.

That choice matters because a home that needs only essentials may be well served by a standby generator in the lower kilowatt range, while a fully electrified home with larger mechanical loads may need substantially more capacity.

Start with your actual electrical loads

Generator sizing is based on load, not square footage alone. Two homes with the same footprint can need very different generators depending on the equipment inside them.

A house with natural gas heat and a gas water heater usually has lower backup power requirements than a home with electric baseboard heat, electric hot water, or large heat pump systems. A private well also changes the picture because the pump motor adds starting load. So does central air conditioning, especially if there are multiple systems or larger compressors.

This is why rough online charts can only get you so far. They can point you in the right direction, but they do not replace a proper assessment of your service, major appliances, HVAC equipment, and starting watt demands.

Running watts and starting watts both matter

Some household equipment needs a brief surge of power when it starts. Motors are the main reason. Well pumps, sump pumps, refrigerators, freezers, air handlers, and air conditioners can all draw more power at startup than they use while running.

If your generator is sized only for steady use, it may struggle when several motor loads cycle on around the same time. A professional load calculation looks at both running demand and startup demand so the system performs reliably when it matters most.

Typical home generator size ranges

For many homes, standby generators fall into a few common size brackets. These are not hard rules, but they are useful for setting expectations.

A smaller standby unit, often around 10 to 14 kW, may cover essentials in a modest home with gas heat and limited heavy loads. This can work well when the priority is keeping food cold, the heat running, the basement dry, and the lights on.

A mid-range generator, often around 16 to 22 kW, suits many homes that want broader coverage. This range can often support essentials plus more convenience circuits, and in some homes it can handle a large percentage of the house if load management is used.

Larger residential units, often 24 kW and up, are commonly considered for bigger homes, electrically heated homes, or households that want whole-home backup with fewer restrictions. If you have multiple HVAC systems, a large well pump, electric cooking, or other high-demand loads, sizing can climb quickly.

The trade-off is simple. More capacity gives you more flexibility and comfort during an outage, but it also raises equipment, installation, and fuel costs. The right size sits in the middle of performance and practicality.

Common household items that affect sizing most

A few loads have an outsized impact on generator size, and they are worth looking at early.

Heating equipment is one of the biggest. If you have a gas or propane furnace, the electrical demand may be fairly modest because the generator mainly powers the blower, controls, and ignition. If you rely on electric resistance heat, the required generator size can jump to a level that makes whole-home backup much less practical.

Air conditioning is another major factor. Homeowners often assume they need every cooling load backed up, but that is not always necessary in an outage. Some prefer to prioritise heating, refrigeration, water, and lighting, then leave air conditioning off to keep the generator size more manageable.

Water systems matter too. A private well pump is a common must-have in New Hampshire homes, and it needs to be accounted for properly. So does a sewage ejector or sump pump if groundwater is a concern.

Kitchen and laundry appliances can push size requirements up fast. Electric ranges, ovens, dryers, and water heaters all demand significant power. If whole-home convenience is the goal, these loads need to be part of the plan.

Why load management can be a smart middle ground

You do not always need a much bigger generator to power more of the house. In some cases, load management lets certain high-demand appliances take turns instead of running at the same time.

That can mean a more efficient system design without giving up too much comfort. It is especially useful when homeowners want broad coverage but do not necessarily need every large load available at once. There is a balance to strike, and this is where a proper site visit pays off.

Portable generator or standby generator?

People often start by comparing a portable generator to a permanent standby system. The sizing question overlaps, but the ownership experience is very different.

A portable generator can cover selected essentials if you are prepared to wheel it out, fuel it, start it manually, and connect it safely through approved transfer equipment. It can be a good short-term solution for some households, but it requires hands-on setup every time the power fails.

A standby generator is permanently installed outside the home and starts automatically when utility power is lost. For homeowners who want dependable backup without scrambling in bad weather, standby is usually the better long-term fit. It is also the better option when outages are frequent, prolonged, or happen while no one is home.

For many households, the question is not just what size generator for my house, but what level of reliability do I want from the system. That answer often points directly to standby power.

Fuel type affects the experience too

Sizing is only part of the decision. Fuel supply matters because it shapes runtime and performance during extended outages.

Natural gas is convenient where available because the fuel supply is continuous through the utility line. Propane is also a strong standby option, especially in rural areas, but the tank needs to be sized appropriately for the generator and expected runtime.

Diesel is less common for residential standby use, though it can make sense in certain applications. The right fuel choice depends on your property, availability, maintenance preferences, and how long outages typically last in your area.

Why professional sizing is worth it

There is a reason experienced installers do not size a standby generator from a quick phone estimate alone. Electrical service details, panel layout, HVAC specifications, fuel supply, transfer switch design, and local code requirements all affect the final recommendation.

A proper assessment helps avoid two common mistakes. The first is undersizing the unit and ending up disappointed during the first serious outage. The second is overspending on capacity you may never use.

A licensed, insured contractor with generator-specific experience can look at your home as a complete system, not just a list of appliance labels. That includes installation quality, maintenance access, and whether the generator will be able to perform reliably year after year. For homeowners who want a dependable answer, that is where local expertise matters.

Generator Power Services approaches sizing that way because backup power is not just about selling equipment. It is about making sure the system fits the property, the loads, and the level of protection the homeowner expects.

A realistic way to think about your next step

If you want the simplest rule of thumb, size your generator around what you cannot afford to lose during an outage, then decide how much comfort you want beyond that. Essentials-only backup usually keeps the project more affordable. Whole-home backup gives you more normal day-to-day living during a power failure, but it requires a larger investment and a more detailed design.

The best answer is rarely a guess pulled from square footage alone. It comes from knowing your loads, your fuel options, and your priorities. Get the system sized to your house properly, and when the next outage hits, the power comes back the way it should - automatically, safely, and without drama.