Quick Answer
What “critical load” means on this page
Here, critical load is household language: the small set of circuits or plug-in appliances you choose to keep alive when utility power fails. It is not a utility tariff term, a demand-response program label, or a promise that every breaker stays on.
Think of it as a filter. Most houses have far more connected watts than a portable—or even a modest standby—can feed at once. The worksheet below forces three honest buckets:
- Must-run — you will power these every outage if the machine can.
- Nice-to-have — only if headroom remains after must-run and the largest surge.
- Leave off — deliberately out of the plan (range, dryer, whole-home AC, spare space heaters).
That filter sits upstream of shopping. Watts without priorities become “run everything,” and the engine bogs. Priorities without watts become a fridge-and-lamps fantasy that forgot the well. Build the list first; then open the sizing guide.
This article pairs with the power outage checklist for homeowners. People, carbon monoxide alarms, and outdoor-only generator placement come before turning circuits on. The load list is step two of a calm sequence—not a reason to ignore safety.
Three layers (stop when the next layer is more house than you need)
Work top-down. Stop when the next layer exceeds your chassis, fuel habits, or transfer path.
Layer 1 — Communications and cold food. Phones and chargers, a lamp or two, router/modem (or a radio), and the refrigerator (and freezer if it shares the plan). Running watts stay modest; the fridge’s compressor is usually the only surge. Apartments and condos often live here forever.
Layer 2 — One habitable zone and water protection. Add one of: furnace blower / controls for a gas or oil system, a window AC or one-zone heat pump conversation, a plug-in or hardwired sump, or a private well. Wells and sumps change the answer more than spare bedrooms. Do not start two large motors in the same minute unless you sized that overlap.
Layer 3 — Everything else stays off. Electric range and oven, electric water heater, central air on its normal cycle, dryer, shop compressor, multiple space heaters, “leave the panel alone.” Layer 3 is a standby-and-load-management conversation—or a deliberate choice to wait for the utility. It is not what most portable owners should promise themselves on paper.
Medical devices (CPAP, oxygen concentrators, other prescribed equipment) are not assigned a layer here and are not prescribed as generator loads. If someone in the household uses powered medical equipment, follow the device manufacturer’s backup notes and the prescribing clinician’s guidance. Do not treat a generic watt table as life-support planning.
Blank critical-load worksheet (copy and fill)
— or use your browser’s print dialog. Nameplate numbers beat table estimates.
Print or copy this table. Fill one row per load. Leave empty rows for items you decide later. Nameplate numbers beat table estimates every time.
| Load | Bucket (must-run / nice / leave off) | Plug-in or hardwired? | Who needs it / why | Running W (nameplate) | Starting W (if motor) | On together? (Y/N) |
|---|---|---|---|---|---|---|
| Refrigerator | ||||||
| Freezer (if separate) | ||||||
| LED lamps / room lights | ||||||
| Router / modem | ||||||
| Phone / laptop chargers | ||||||
| TV (optional) | ||||||
| Sump pump | ||||||
| Well pump | ||||||
| Furnace blower / controls | ||||||
| Window AC or one zone | ||||||
| Microwave | ||||||
| Coffee maker | ||||||
| Garage door opener | ||||||
| Space heater | ||||||
| Electric range / oven | ||||||
| Other: ________ |
Scoring rules
- Mark must-run only for loads you will actually keep alive every outage.
- Mark plug-in vs hardwired. Hardwired well, furnace, or sump need a legal inlet with interlock or transfer switch—cords alone will not feed them. See transfer switch vs interlock.
- Fill who needs it in one short phrase (food, basement, heat in bedroom, work laptop). Vague “nice to have everything” rows get demoted.
- Record running and starting from the nameplate when possible. Use the wattage library below only as a planning placeholder until you walk the house.
- Check on together. If two motors can start in the same minute, note that—your peak is no longer “one largest surge.”
Wattage library (planning estimates only)
Ranges below are planning estimates for worksheet drafting—not lab measurements, not model claims, and not a substitute for the sticker or plate on your equipment. Locked-rotor amps, hard-start kits, age, and voltage all move the numbers. Your nameplate wins.
| Load | Typical running (planning) | Typical starting / surge (planning) | Notes |
|---|---|---|---|
| Refrigerator | 100–250 W | 600–1,200 W | Cycles; often the Layer-1 surge |
| Freezer (chest or upright) | 100–300 W | 600–1,400 W | Same idea as fridge; confirm plate |
| LED lamps / lighting circuit | 10–150 W | — | No motor surge |
| Router / modem / ONT | 10–40 W | — | Keep communications |
| Laptop charge | 45–100 W | — | Peak while charging |
| Phone chargers (each) | 5–20 W | — | Low continuous |
| LED TV | 50–200 W | — | Nice-to-have for many lists |
| Sump pump (plug-in) | 800–1,500 W | 1,500–3,000 W | Basement protection; confirm cord vs hardwired |
| Well pump | 750–2,500 W | 2,000–6,000+ W | Wide range; 120 vs 240 V matters a lot |
| Furnace blower (gas/oil heat) | 400–1,000 W | 800–2,000 W | Heat without electric strips |
| Window AC (small–mid) | 500–1,500 W | 1,000–3,000 W | One room, not whole-home |
| Microwave | 800–1,500 W | — | High running; short duty |
| Coffee maker | 800–1,500 W | — | Often leave off during motors |
| Space heater (portable) | 1,000–1,500 W | — | Discourage as default—see traps below |
| Garage door opener | 300–600 W | 600–1,200 W | Brief use; often nice-to-have |
| Electric range / oven | 2,000–5,000+ W | — | Steady high draw; usually leave off |
| Electric water heater | 3,000–4,500 W | — | Steady; usually leave off on portable plans |
Well pump range note: Private wells vary more than almost any other residential load. A shallow 120-volt jet pump and a deep 240-volt submersible are different machines. Treat the row above as a flag that “water is on the list,” then read volts × amps (and locked-rotor if printed) from the controller or motor plate before you size.
How to read a nameplate (and use one surge)
If the plate lists watts, use that for the running column. If it lists volts and amps but not watts:
Watts = volts × amps
Examples of the method (illustrative arithmetic, not claims about your gear): a 120 V device at 6 A ≈ 720 W running; a 240 V pump at 8 A ≈ 1,920 W running.
For motors, look for locked-rotor amps (LRA), starting watts, or a separate surge figure. Worksheet math that keeps people out of trouble:
- Add all running watts for loads that may be on together.
- Find the one item with the largest starting figure.
- Add only the extra start (starting − that item’s running) to the running total.
- Compare running total to continuous generator rating, and peak to surge rating—with headroom.
Do not sum every motor’s surge unless they truly start together. Stagger the well and the furnace blower. Nameplates and manufacturer notes beat memory; yellow energy stickers are often annual kWh, not running watts.
When the list is filled, take the running total and planning peak to the generator sizing guide. That guide is the primary next step for turning a worksheet into a portable or standby category.
Transfer path reminder (cords vs inlet)
The worksheet column plug-in vs hardwired decides the hookup story:
- Plug-in only (fridge, lamps, modem, window AC, many sumps): outdoor-rated cords of adequate gauge can be enough for short outages—machine outdoors, away from openings.
- Hardwired (well, furnace blower, hardwired sump, selected lighting circuits): you need a permitted inlet with an interlock or manual transfer switch, or a standby ATS. Never backfeed a dryer or range outlet.
Watts without a legal feed still leave the well dark. Read transfer switch vs interlock before treating a portable as “the house generator.”
High-watt traps: space heaters and electric cooking
Two load classes quietly break portable plans:
Portable space heaters often draw 1,000–1,500 W each, continuously, with no “surge discount” to hide behind. One heater can consume the headroom you needed for the fridge surge. Prefer a gas/oil furnace blower on a managed circuit, layered clothing, and one conditioned room—not three heaters “just for comfort.” Mark heaters leave off unless you have measured headroom after must-run motors.
Electric ranges, ovens, and many cooktops are multi-kilowatt steady draws. So are most electric water heaters. Keeping them as soft “maybes” forces a standby-sized quote when a kettle, camp stove (used safely outdoors or per its manual), or gas cooktop would have kept you in a portable band. Put them in leave off unless you have already chosen a managed whole-home path.
Microwaves and coffee makers are shorter duty cycles but still high running watts—run them only when large motors are idle.
Worked example A — apartment: fridge + communications
Setting: Rental or condo. No private well. No tenant-controlled furnace on the generator plan. Outdoor gasoline placement may be restricted; if so, a battery/station path may replace a fueled portable—see battery backup vs generator. Numbers below are illustrative plates a renter might record, not averages.
| Load | Bucket | Path | Running W | Starting W |
|---|---|---|---|---|
| LED lamp + phone chargers | Must-run | Plug-in | 80 | — |
| Router / modem / laptop | Must-run | Plug-in | 70 | — |
| Refrigerator | Must-run | Plug-in | 180 | 800 |
| TV | Nice-to-have | Plug-in | 100 | — |
| Space heater | Leave off | — | — | — |
Must-run running total (fridge on): 80 + 70 + 180 = 330 W
Extra surge (fridge only): 800 − 180 = 620 W
Planning peak: 330 + 620 = 950 W
Add the TV only if the machine has continuous headroom after the fridge cycle. Success is charged phones and cold food—not whole-apartment HVAC. No inlet required if everything stays corded; never invent a dryer-outlet backfeed.
Worked example B — house with well + furnace blower
Setting: Detached house, private well (hardwired), gas furnace with electric blower, fridge, lights, modem. Electric range stays off the plan. Someone can start a portable most evenings. Illustrative plates only.
| Load | Bucket | Path | Running W | Starting W |
|---|---|---|---|---|
| Refrigerator | Must-run | Hardwired or plug-in | 180 | 800 |
| LED lights + modem + phones | Must-run | Mixed | 150 | — |
| Furnace blower | Must-run (one zone) | Hardwired | 720 | 1,400 |
| Well pump | Must-run | Hardwired 240 V | 1,920 | 4,800 |
| Microwave / coffee | Nice-to-have | Plug-in | ~1,000 | — |
| Electric range | Leave off | — | — | — |
| Space heaters | Leave off | — | — | — |
Running if fridge + lights + blower + well may be on: 180 + 150 + 720 + 1,920 = 2,970 W
Largest extra surge (well): 4,800 − 1,920 = 2,880 W
Planning peak (one motor start): 2,970 + 2,880 = 5,850 W
Operating rule: do not start well and blower in the same minute. Run microwave only when the well is idle. Cords alone cannot feed this list—budget a permitted inlet with interlock or manual transfer after sizing. Full method and chassis bands live in the sizing guide; hookup detail lives in transfer switch vs interlock.
Same storm season as Example A; opposite worksheet. The buckets and hardwired column decide—not square footage.
Pair the worksheet with the outage checklist sequence
Fill this page on a calm day. When the lights fail, do not open with the watt table.
- People and CO first — household check, working alarms, flashlights. Generator outdoors only if you use one.
- Fridge doors closed — food-safety habits from the outage checklist.
- Only the must-run set you already sized — then one motor at a time.
- Transfer sequence as posted — utility off / generator path on only as labeled; no improvisation.
- After restoration — note what you actually used; demote rows that stayed dark; restock fuel and rotate.
A worksheet without a checklist becomes a second emergency. A checklist without a worksheet becomes “run everything.” Keep both with the manuals.
From list to size (education before commerce)
You now have buckets, paths, and planning watts. Next:
- Confirm the two or three largest nameplates with a phone flashlight.
- Compute running total + one largest extra surge (or a known overlap).
- Read the generator sizing guide for continuous vs surge, priority layers, and portable vs standby bands.
- Decide cords vs inlet vs standby with transfer switch vs interlock and portable vs standby generators.
- Rehearse placement and the interlock card once with the main still on—dry run only.
No brand models, no “buy now,” no storm-fear countdown. The goal is a written list you trust when you are tired.
Next step
- Generator sizing guide — turn this worksheet into continuous and surge planning numbers.
- Power outage checklist for homeowners — people, CO, fridge protocol, first-30-minutes drill (Outage hub parent).
- Transfer switch vs interlock — cords vs inlet once hardwired loads are on the list.
- Portable vs standby generators — chassis after watts and who will be home.
- Battery backup vs generator — quieter path when outdoor exhaust is not allowed.