Why Square Footage Is a Bad Input

Manufacturer guides that say “18kW covers up to 3,000 square feet” are marketing averages, not engineering. A 3,000 sq ft cabin with a heat pump, a hot tub, an electric range, an electric water heater, and a dryer has a completely different peak load than a 3,000 sq ft cabin with gas appliances and no amenities. The only valid sizing input is the sum of your actual loads. Call (865) 256-0876 and we’ll run the calculation before you order anything.

Essentials vs. Whole-Home Coverage

Essentials-only coverage via a critical-load sub-panel typically includes: well pump, refrigerator, one HVAC zone, some lighting, and select outlets. It uses a smaller generator and a smaller transfer switch. The cost difference between essential and whole-home coverage is usually $1,500 to $3,000. For a primary residence or a year-round rental cabin where guests expect all amenities to work during an outage, whole-home is the right choice. Call (865) 256-0876.

Matching the Generator to Your Cabin

For a typical Sevier County cabin: one mini-split HVAC zone (about 5kW running load), a water heater (4.5kW), a hot tub heater (4kW running), a refrigerator (0.5kW), and lighting and general outlets (2 to 3kW) total roughly 16 to 18kW of running load. An 18kW standby generator handles this with standard starting current margin. Two HVAC zones or a larger hot tub pushes to 22 to 24kW. We size to running load plus starting current, not just nameplate watts. Call (865) 256-0876.

The Transfer Switch Determines Coverage Scope

A 200A automatic transfer switch (ATS) for whole-home coverage runs more than a 50A or 100A ATS for essential loads. For a cabin where guests expect all amenities, the 200A ATS with whole-home generator is the right specification. Call (865) 256-0876 or contact us. See our gallery.

Starting Current: What Kills Undersized Units

Running watts are only half the sizing problem. Motors draw a multiple of their running current for the moment they start, and an HVAC compressor’s locked-rotor draw can be three to five times its running load. A generator sized to the running numbers alone starts the cabin fine, right up until the heat pump cycles on mid-outage and the voltage sags, lights dim, electronics brown out, and the generator either rides through ugly or trips offline.

Sizing for it is straightforward when it is actually done: the calculation carries the largest motor’s starting demand on top of the running load, and the unit is chosen to absorb it. Soft-start kits on HVAC compressors change the math meaningfully, knocking the starting surge down enough that a smaller generator handles a cabin it otherwise could not. That kit is often the cheapest kilowatts on the whole project. We run both versions of the numbers and tell you which combination wins. Call (865) 256-0876.

Load Management: Run More Cabin on Less Generator

Modern transfer switches support load-shedding modules that make a mid-size generator behave like a bigger one. The logic is simple: the water heater and the hot tub do not need to run during the ninety seconds the HVAC compressor is starting. The module holds the deferrable loads back momentarily, lets the big motor start clean, then restores everything. Guests notice nothing; the generator never sees the worst-case stack-up.

On paper this can be the difference between a 22 kW and an 18 kW unit carrying the same cabin, which is real money at purchase. It is not the right answer everywhere; a property whose loads are all essential all the time needs the capacity outright. But for rental cabins with a hot tub and electric water heating, managed loads are often the smart spec. We design the shed priorities around how the property actually gets used. Contact us to look at the numbers.

The Fuel Side of Sizing

A generator’s nameplate assumes its fuel supply can feed it, and that assumption fails quietly. On natural gas, the meter and the line to the pad must deliver the unit’s full BTU demand on top of the furnace, the water heater, and the range; an undersized gas line shows up as a generator that starts, struggles under load, and shuts down looking like a mechanical failure. On propane, cold matters: a small tank in single-digit weather cannot vaporize fuel fast enough for a large engine, no matter how many gallons it holds.

So the sizing visit covers the fuel path too: meter capacity, line sizing, tank size against winter vaporization rates. It is unglamorous pipe math, and skipping it is one of the most common reasons a bargain install disappoints during its first real outage. Ours includes it every time. Call (865) 256-0876.