By Nic Taylor, Master Electrician, ZAP Industries (formerly ZAP Electric), Dickinson, ND

On a January night in western North Dakota, it can be thirty below with a wind that rattles the siding, and then the power drops out. Within a few hours the house is cooling fast, the sump pump has stopped, and you’re thinking about frozen pipes. A standby generator is built for exactly that night. It only helps, though, if it’s big enough to run what you actually need.

We’ve installed and serviced generators from Dickinson to Williston and down the I-94 corridor to Mandan and Bismarck. The most common mistake we see is a generator that’s the wrong size. An undersized unit trips or bogs down when the furnace and well pump start at the same time. An oversized one costs more to buy, install, and fuel than it needs to. Here’s how to get the size right.

Step 1: Decide what has to run

Start by choosing one of two approaches:

• Essential circuits only. This covers the furnace, well pump, sump pump, fridge and freezer, some lights, outlets for phones and internet, and maybe a garage door opener. It needs a smaller generator and usually a smaller transfer switch.
• Whole home. Everything runs as usual, including the electric range, dryer, water heater, central air and shop circuits. It needs a bigger unit, but you don’t have to pick and choose during an outage.

In North Dakota, heat comes first, then water. If you can keep the furnace and water running, you can ride out almost any outage.

Step 2: Know your heat source

Your heating system matters more than anything else on the list:

• Natural gas or propane furnace: the blower motor only needs a few hundred watts. Most homes with gas heat do fine on a mid-sized generator.
• Electric heat (baseboard, electric furnace, or heat pump with backup strips): electric resistance heat draws a lot of power. A 15–20 kW electric furnace can need a generator as big as everything else in the house combined. Homes with electric heat often need a whole-home unit, or a plan for running only some heat zones.
• In-floor heat with an electric boiler: treat it the same as electric heat.

Step 3: Account for starting loads

Motors pull a big surge for a second or two when they start. Well pumps, sump pumps, air conditioners, and some furnace blowers can briefly draw two to three times their running power. Your generator has to handle that surge. That’s the main reason a “close enough” guess fails.

Rough running loads to plan around:

Item	Approximate running watts
Gas furnace blower	500–800
Well pump (1 HP)	1,000–1,500 (surge much higher)
Sump pump	800–1,000
Refrigerator / chest freezer	150–700 each
Lights, internet, TV	500–1,000
Microwave	1,000–1,500
Electric water heater	4,500
Central A/C (3 ton)	3,500–4,500
Electric range / dryer	3,000–5,500 each

These are ballpark numbers. Nameplates on your equipment give the real ones.

Step 4: Add it up and leave headroom

Add up the running watts of everything that has to run together. Then add the single biggest starting surge on top. Leave about 20% headroom so the generator isn’t running at full output for days. Here are typical results:

• Gas heat, essentials only: often 10–14 kW
• Gas heat, whole home with central air: often 18–24 kW
• Electric heat or large shop loads: often 26 kW and up, sometimes with load management

Step 5: Don’t forget fuel and the transfer switch

• Fuel: natural gas is the easiest if you have it. Out on a farm or acreage, propane is the usual choice. Your tank has to be big enough to run several days, and propane loses capacity in deep cold, so tank size matters. We’ll help you figure your run time.
• Transfer switch: an automatic transfer switch (ATS) starts the generator and moves your home onto it within seconds, even if you’re away. It also keeps power from feeding back onto utility lines, which protects line crews. North Dakota requires a permitted, inspected installation by a licensed electrician.
• Placement: the unit needs clearance from windows, doors, and vents. It should sit on a solid pad, out of drifting snow, where it’s easy to service.

Step 6: Plan for North Dakota winters

Ask about a cold-weather kit, such as a battery warmer and oil heater, so the generator starts reliably at −30°F. Schedule maintenance once a year, ideally in the fall before the first big storm. Weekly self-tests catch problems before you need the generator.

Get a size you can count on

You don’t need to do the math alone. Fill out our free generator sizing form. Tell us your heat source, well or city water, and what you want to keep running, and we’ll recommend a size. When you’re ready to compare units, browse the generators in our shop.

ZAP Industries is a licensed North Dakota electrical contractor (License #000047000) based in Dickinson. We take calls 24/7 and offer weekend emergency service.

Call (701) 513-9012 or email ntaylor@zapelectric.llc to schedule a sizing visit before the next storm hits.