Sizing worksheet (critical circuits)

For: Homeowners preparing notes for a licensed electrician or standby dealer. This is a conversation worksheet — not an engineering calculation and not a substitute for NEC Article 220 load work.

First decision: critical circuits vs whole-home

• Critical / essential: Keep fridge, freezer, well or sump, furnace blower / heat source, a few lights/outlets, medical devices, modem/router, maybe one AC zone. Smaller generator + selective transfer often costs less.
• Whole-home: Aim to run most of the house during an outage. Larger standby unit, bigger fuel demand, more site work. Still needs a real load calc — not “match the main breaker.”

Write this down before the site visit

1. Service size on the main panel label (e.g. 100A / 200A) — for context only.
2. Fuel available at the property: natural gas meter? Propane tank size/location? Diesel preference?
3. Outage pattern: hours vs days; winter vs summer; anyone home overnight?
4. Must-run list (check what applies):
   • Refrigerator / freezer
   • Well pump or municipal booster
   • Sump / sewage ejector
   • Furnace / heat pump / boiler controls
   • Medical equipment (CPAP, oxygen concentrator, etc.)
   • Home office / networking
   • Range / cooktop (often dropped on critical-only plans)
   • Electric water heater or HPWH
   • Central AC or heat pump outdoor unit
   • EV charger (usually shed during outage unless sized for it)
   • Other: _______________
5. Nameplate photos: HVAC outdoor unit, well pump controller, electric dryer/range if you hope to run them.
6. Utility peak-demand history if your bill or app shows kW peaks (helpful cross-check for pros — optional).

What your electrician / dealer should do (not you)

• Perform a code-aligned load calculation (often NEC dwelling methods) for the circuits the standby system will serve.
• Account for largest motor starting (well, AC compressor) and any load-management / soft-start options.
• Match transfer equipment to the generator type (standby → typically ATS).
• Check panel condition, grounding/bonding, and whether a service or subpanel change is in scope.

Shopping ranges you will hear (context only)

Dealers often talk in rough kW bands (e.g. ~10–14 kW critical, ~18–24 kW common whole-home for many single-family homes). Treat those as marketing conversation starters. Your home can be smaller or larger. Do not buy from a social-media kW chart alone.

Bring this packet to the bid

• This worksheet filled in
• Photos of the main panel (door label + interior with cover off — only if a pro opens it safely)
• Preferred must-run list ranked 1–10
• Questions from the permit page and fuel page

Next: permit / inspection path →