How to Size a Home Backup Generator in the Mat-Su Valley

If you’re thinking about a backup generator, the first real question isn’t which brand to buy, it’s what size you actually need. Get it right and your home rides out a winter outage without you thinking twice. Get it wrong and you either pay for far more generator than you’ll ever use, or you find out at 20 below that the unit can’t carry your well pump and your furnace at the same time. Here’s how we size a standby generator for a Mat-Su Valley home, in plain terms.

Start with what you want to keep running

Before we talk kilowatts, we talk priorities. There are really two ways to approach backup power:

• Essential circuits only. Heat, well pump, refrigerator and freezer, and a few lights and outlets. This keeps your pipes from freezing, your water running, and your food safe, and it’s the most budget-friendly path.
• Whole-home backup. Everything runs like the grid never went down, including the range, the dryer, and every outlet in the house. More capacity, more cost, more convenience.

Neither answer is wrong. It comes down to your home, your budget, and how you want to live through an outage that might last a few hours or a few days.

The loads that matter most in Alaska

Sizing here isn’t the same as sizing a generator in a mild climate. In the Valley, a handful of loads carry real weight:

• Heat. Whether you’re on a boiler, a furnace, or a heat pump with electric backup, losing heat in the dead of winter is the emergency. Electric heat strips in particular draw a lot of power and can drive the whole calculation.
• Well pump. Most Valley homes are on a private well. Well pumps pull a heavy surge of power the moment they start, often several times their running draw, and that starting surge has to fit inside the generator’s capacity.
• Refrigerator and freezer. Plenty of Alaska families have a season’s worth of moose or salmon in the freezer. That’s not a small thing to lose.
• Everything else. Lights, outlets, the garage door, well-house heat tape, and any medical equipment in the home.

Why the starting surge is the tricky part

The single most common sizing mistake we see is adding up the running watts on the nameplates and calling it a day. Motors, and your well pump and furnace blower are motors, draw a big spike of power at the instant they start, well above what they use once they’re running. A generator has to have enough headroom to swallow those surges without stumbling, especially when two motors happen to kick on at once. This is exactly why a real load calculation beats a rule of thumb.

What a load calculation actually looks like

As an Authorized Cummins dealer, we do an in-home load calculation before we ever quote a unit. That means we walk your home, look at your actual electrical panel, note your heat source, your well pump, and your major appliances, and factor in both running and starting loads. From there we match you to the right Cummins Quiet Connect unit, which range from 13kW and 17kW for essential-circuit setups up through 20kW and larger for whole-home coverage, and up to 100kW for commercial jobs. No guesswork, and no oversized quote just to pad the ticket.

A rough starting point (before we measure)

Every home is different, but to give you a general sense before we come out:

• A 13kW unit is often enough to cover the essentials in a modest, gas-heated home with a standard well.
• A 17kW to 20kW unit is a common whole-home choice for an average Valley house.
• Homes with electric heat, large shops, multiple well pumps, or a lot of square footage frequently need more, which is exactly what the load calculation is for.

Treat these as a conversation starter, not a final answer. The only number that matters is the one that comes out of measuring your specific home.

Don’t forget the transfer switch

A generator is only half the system. The transfer switch is what actually connects that generator to your home safely and, in the case of an automatic switch, what starts the unit and restores power on its own when the grid drops. When we size a generator, we size the transfer switch and the connected loads right along with it. You can read more about your options on our transfer switch installation page, or see the full picture on our home backup generator installation page.

Frequently Asked Questions

What size generator do I need to run my whole house?

For an average Mat-Su Valley home, whole-home backup often lands in the 20kW range, but electric heat, a big shop, or higher square footage can push it higher. The honest answer is that it depends on your actual loads, which is why we do a free in-home load calculation before recommending a unit.

Can a backup generator run my well pump?

Yes, and for most Valley homes keeping the well pump running is one of the main reasons to install one. The key is making sure the generator has enough headroom for the pump’s starting surge, which we account for when we size the system.

Is it bad to buy a generator that’s too big?

An oversized generator costs more up front, burns more fuel, and can actually run less efficiently under a light load. Bigger isn’t automatically better. The goal is the right size for your home, not the biggest one on the lot.

Let’s size the right generator for your home

The best way to know what you need is to have a licensed electrician measure it. Call AK Sparky’s Electric at 907-671-9288 or schedule online, and we’ll do an in-home load calculation and walk you through your options, with upfront pricing and no pressure.