How these numbers are produced
Everything here is a planning estimate built from published manufacturer figures and stated assumptions. Where we could not verify something, the page says so.
Why ranges instead of a number
A refrigerator does not have "a wattage". It has a compressor that cycles on and off, and how much energy it uses over a day depends on the unit's age and efficiency, the temperature of the room, and how often the door opens. Across common household units that is a spread of several times over.
A calculator that reports a single runtime figure has resolved that uncertainty by picking one value and not telling you. We show the whole range, and we size on the higher number.
The sizing rules
- Running watts are summed across every load you select, treating them as concurrent.
- Starting watts add only the single largest startup surge on top of the running total. Modelling every motor starting simultaneously would be unrealistically pessimistic; ignoring startup entirely is how undersized systems get recommended.
- Energy is running watts × hours × duty cycle, computed at both ends of the band.
- Usable battery energy is 85% of the nameplate rating where the manufacturer does not publish a usable figure, because inverter losses, cell cutoffs and cold weather all take a share.
- Runtime is usable energy divided by your concurrent draw. Higher draw gives the shorter runtime, so the short end of the runtime band pairs with the high end of the load band.
What we will never rank
A product is shown for research but never ranked, never recommended and never given a buy link when:
- its recall or model identity is unresolved
- a required specification is missing, so it cannot be sized honestly
- it would need building wiring that we cannot verify for your situation
The planner enforces this before it does any sizing, so a suppressed product cannot reach a result page by being a good fit on paper.
How we decide a fact is solid
- A specification is recorded only when it appears on a manufacturer page or manual that we fetched, with the URL and capture date stored alongside it.
- Figures seen only in a search result summary, a retailer listing or a review are not recorded.
- We do not borrow a figure from a similar model in the same product family. A missing field stays missing.
- Regional applicability matters: a European manual is not a source for a US-market unit, because voltage and outlet configuration differ.
- Accessory compatibility records the manufacturer's own wording, because "sold on the same page" is not the same claim as "compatible with this model".
Current coverage across the 12 anchor stations: 127 of 144 required fields captured, 13 needing confirmation, 4 not captured.
What this site does not do
- Not an electrical design, and not a code or permit determination.
- Not a life-safety or medical guarantee.
- Not a promise that a system will keep your home safe.
- Not a substitute for reading the nameplate on your own appliances.
Sources
- Product specifications — manufacturer product pages and user manuals, captured with URL and date.
- Recall data — the US Consumer Product Safety Commission recall database.
- Appliance load ranges — category ranges across common household units, given as bands rather than point estimates, with the confirmation step you should take stated on each load page.
Corpus built 2026-08-13. The planner in your browser runs the same logic as our reference implementation, held together by generated parity tests, so the published calculator and the tested calculator cannot drift apart.