Observed arrival · 2026-09-15

Watts Math: Home Electrical and HVAC Calculators That Show Their Work

wattsmath.com Observed source

Editorial interest 82/100 Selection signal · not a rating of the site

A free set of browser-based calculators for wiring, circuits, heating, cooling, generators, electricity costs, and solar sizing.

Landing page captured for the 2026-09-15 issue.

Field notes

The calculators divide a broad household-planning problem into concrete jobs: conductor resistance and ampacity, HVAC load estimates, generator starting surge, appliance kWh, and solar production. The site identifies sources including NEC Chapter 9 Table 8, NEC 310.16, ENERGY STAR, EIA, and NREL PVWatts. Its own warning distinguishes general-code estimates from conduit fill, local amendments, terminal ratings, inspector judgment, and the Manual J process.

Observed signals

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Editorial observations of this landing page, not a rating.

○OpenPublic substance visible

✦PrettyNotable craft visible

●ProPolished or operationally mature

◎NicheUnusually specific use

ƒJavaScriptBrowser-side code central

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