What Size Standby Generator Does Your Maine Home Need?

When a winter nor’easter or an ice storm rolls through Central Maine and the power goes out, the first question most homeowners ask isn’t about brand names or model numbers — it’s “how big a generator do I actually need?” It’s a fair question, and the honest answer is that proper sizing doesn’t start with a number on a spec sheet. It starts with a decision: what do you want to keep running when the grid goes dark? Get that right, and the size follows naturally. Guess at it, and you either overspend on capacity you’ll never use or come up short on the night you needed it most.

As a veteran-founded contractor licensed for both electrical and HVAC work in Maine, New Hampshire, and Massachusetts, we install standby generators for homeowners and light-commercial properties across Central Maine, the Kennebec Valley, and the Midcoast. Here’s how we think about sizing a standby unit — and why the most reliable answer comes from an on-site visit rather than a calculator on a website.

Sizing Starts With a Decision, Not a Model Number

A standby generator’s job is to carry electrical load. The more of your home you want it to carry at once, the more capacity it needs. So before anyone can recommend a unit, the real work is figuring out what “keeping the lights on” means for your household. For one family that means the whole house runs as though nothing happened. For another it means the heat, the water, and the fridge stay on, and everything else can wait until the utility crews finish. Both are valid — they just point to different-sized machines.

This is why a thoughtful installer asks questions before quoting a size. Your answers shape the load, and the load shapes the generator.

Whole-Home vs. Essential-Circuits: Two Honest Approaches

There are two broad strategies for backing up a Maine home, and the right one depends on your priorities and your budget.

The whole-home approach

A whole-home setup is sized to run essentially everything in the house at the same time, so an outage feels like a non-event. You don’t think about which appliances are on. The trade-off is that this calls for a larger unit and a larger fuel supply, because the generator has to be ready for your peak demand rather than your average demand.

The essential-circuits approach

An essential-circuits setup powers a chosen group of must-run circuits — your heat, your well pump, your refrigerator, and a few key outlets and lights — while leaving the power-hungry extras dark. It typically uses a smaller, more economical generator and less fuel. For a lot of Maine households, this hits the sweet spot: you stay warm, safe, and fed through a multi-day outage without paying to run the whole house.

Neither approach is “better” in the abstract. The point of an on-site assessment is to match the strategy to how you actually live and what your panel and property can support.

The Loads Maine Homes Prioritize in an Outage

In our climate, the stakes during an outage are different than in a milder part of the country. A power loss in January isn’t just an inconvenience — if the heat goes off, pipes can freeze and burst, turning a one-night outage into a serious repair bill. So when we sit down to plan a system, certain loads come up again and again as the things people refuse to lose.

• Your heating system and its blower or circulator. Even a furnace or boiler that burns oil, propane, or natural gas still needs electricity to run its blower, pumps, and controls. No power means no heat, regardless of the fuel.
• The well pump. If you’re on a private well — and much of rural Maine is — no electricity means no running water for drinking, cooking, or flushing.
• The refrigerator and freezer. Protecting a full freezer of food through a long outage is a real and recurring concern for our customers.
• The sump pump. When a storm brings both an outage and heavy water, a dead sump pump can mean a flooded basement.
• Internet and medical equipment. For anyone working from home or relying on powered medical devices, these aren’t optional.
• Key lighting and outlets. Enough light to live by and outlets to charge phones and run small essentials.

Typical must-run loads	Common nice-to-have loads
Heating system blower, pumps & controls	Central air conditioning
Well pump	Electric range & oven
Refrigerator & freezer	Electric clothes dryer
Sump pump	Hot tub or spa
Internet & medical equipment	Workshop or garage equipment
Essential lighting & outlets	Whole-home, every-circuit operation

Where each item lands on that list is a personal call. The table is a starting point for the conversation, not a fixed rule — some households consider central cooling essential, and some can live without a clothes dryer for a few days without a second thought.

How Electric vs. Fuel-Fired Heating Changes the Picture

Few things move the needle on generator sizing as much as how your home makes heat, and this is exactly where having an HVAC perspective on the sizing matters.

A fuel-fired heating system — oil, propane, or natural gas — gets its heat energy from the fuel itself. The generator only has to power the electrical parts: the blower motor, circulator pumps, igniter, and controls. That’s a comparatively modest electrical load.

Electric heat is a different story. Electric furnaces, electric baseboard, and the supplemental heat strips in many heat pump systems draw a substantial amount of electricity to produce warmth. A home heated this way generally needs a meaningfully larger generator to keep up — and that’s a detail easy to miss if whoever is sizing the unit doesn’t understand how your heating equipment actually behaves. Because we work on both the electrical and the HVAC sides, we account for the real demand of your specific heating system instead of treating it as a generic line item.

Why a Proper Load Calculation Beats Guessing

You’ll see plenty of rough rules of thumb online, and they’re fine for daydreaming. But the honest way to size a standby generator is a load calculation performed on-site by someone who can actually look at your panel, your equipment, and your wiring.

A real calculation accounts for things a generic estimate can’t: the specific motors in your home and the extra surge of power they pull at the instant they start, how your largest loads overlap, the condition and capacity of your existing electrical panel, and the realistic peak you’ll hit on the coldest, busiest evening. The goal is a generator that’s big enough to do the job confidently but not so oversized that you’ve paid for capacity and fuel you’ll never touch. That balance is something you find by measuring, not by guessing.

If your assessment turns up an older or undersized panel, that’s worth knowing early — sometimes a standby installation pairs naturally with an electrical panel upgrade so the whole system is sound from the meter inward.

Fuel Options: Decide Up Front

A standby generator needs a fuel source, and in most of our service area that means propane or natural gas. This is a decision to make at the planning stage, not an afterthought, because it shapes the installation.

If your home already has natural gas service, tying the generator into that supply can be straightforward. Much of rural Maine, though, runs on propane, which means planning for an appropriately sized tank and its placement, along with the gas line to the unit. Either way, the fuel plan, the generator, and the electrical work all have to be designed together so the system is ready to run for as long as an outage lasts — and so it’s sized to keep the generator fed at the demand you’ve chosen to back up.

The Automatic Transfer Switch Is Not Optional

A standby generator is only half the system. The other half is the automatic transfer switch — the device that senses when utility power drops, safely disconnects your home from the grid, starts the generator, and switches your circuits over. When the utility comes back, it switches you back and shuts the generator down. All of it happens on its own, often before you’ve fully registered that the lights flickered.

That transfer switch has to be wired into your electrical panel by a licensed electrician. This isn’t a corner to cut. A switch that’s wired incorrectly can backfeed power onto the utility lines — a genuine danger to the line crews working to restore your neighborhood — and it can put your home and family at risk. Proper, code-compliant integration with your panel is what makes a standby system safe, and it’s exactly the kind of work our licensed electricians handle on every install. You can read more about our broader residential electrical work and how we approach safety.

The Dual-Trade Advantage: One Team for the Whole Job

Here’s where being licensed for both electrical and HVAC genuinely changes the experience. A standby generator installation touches several disciplines at once: the generator and its fuel, the transfer switch, the panel work, and a load calculation that has to correctly account for your heating and cooling equipment. On many projects, those pieces get split among different trades who have to coordinate — and the seams between them are where mistakes and finger-pointing live.

Because we’re a single licensed electrical-and-HVAC team, the generator, the transfer switch, the panel work, and the HVAC-aware load calculation are all handled under one roof. The person figuring out how much electricity your furnace or heat pump really draws is on the same team as the electrician wiring your transfer switch. Nothing falls through the cracks between trades, because there are no cracks. You can learn more about how we work as a combined electrical and HVAC contractor in Maine, or explore our dedicated standby generator services. For businesses, we offer the same approach through our commercial generator work.

The Right Size Comes From a Free On-Site Assessment

There’s no responsible way to hand you a generator size from behind a keyboard, and we won’t pretend otherwise. The right size for your Maine home comes from a free on-site assessment — a real visit where we look at your panel, your heating and cooling equipment, your well and water setup, and the loads that matter most to you, then run an honest load calculation around them. From there we can recommend a unit and a fuel plan that fit your home, your priorities, and your budget — and back it all with a single licensed team.

If a winter without heat or water isn’t a risk you want to keep taking, contact us to schedule your free on-site generator assessment. We’ll help you figure out exactly what your home needs to keep running — and make sure it’s installed safely, by the people who sized it.

Common Questions

How do I know whether I need a whole-home generator or just essential circuits?

It comes down to how you want an outage to feel and what you’re comfortable spending. If you want the house to run as though nothing happened, a whole-home system makes sense. If you mainly want to protect your heat, water, food, and a few essentials through a multi-day outage, an essential-circuits approach is usually more economical. During a free on-site assessment we walk through your priorities and your panel together so the strategy fits your household rather than a generic template.

Does the type of heating in my home really affect the generator size?

Significantly. A fuel-fired furnace or boiler — oil, propane, or natural gas — only needs the generator to power its blower, pumps, and controls, which is a relatively light electrical load. Electric heat, including electric furnaces, baseboard, and the supplemental strips in many heat pumps, draws a large amount of electricity and generally calls for a bigger generator. Because we handle both electrical and HVAC, we account for how your actual heating equipment behaves instead of guessing.

Can I install the transfer switch myself to save money?

This is one area where we strongly advise against do-it-yourself work. The automatic transfer switch ties directly into your electrical panel, and if it’s wired incorrectly it can backfeed power onto the utility lines and endanger the crews working to restore power — as well as your own home. It needs to be installed by a licensed electrician and integrated with your panel to code. That safe, correct integration is part of every standby installation we do.

Why is an on-site visit necessary instead of an over-the-phone estimate?

Because an accurate load calculation depends on details we can only verify in person: the specific motors and appliances in your home and the extra power they pull when they start, the condition and capacity of your existing panel, how your largest loads overlap, and the realistic peak demand on a cold Maine night. A figure quoted over the phone is a guess, and guessing leads to a generator that’s either oversized and wasteful or too small to do the job. The on-site visit is how we get it right, and it’s free.