Browser micro-tools
Free HVAC calculators you can run in a browser.
Lightweight calculators you can open in a browser for a fast answer — then take the matching offline app when the crawlspace has no signal. Estimating aids for qualified techs only.
Tools
Free web tools
These are the calculations a tech actually reaches for between calls: how big does the equipment need to be, how big does this duct run need to be, and is this system charged right. Each one runs entirely in your browser — nothing is sent to a server, nothing is saved, and there is no email gate in front of the answer.
They are deliberately narrow. Each tool answers one question well and then points you at the app that does the full job offline, because a browser tab is the wrong place to be standing in a mechanical room with no signal. Every result states the assumptions it made, and every tool says plainly where its scope ends.
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Live
Free online Manual J calculator
Whole-house heating and cooling load from eight inputs, using real 99% / 1% design temperatures resolved from your ZIP code rather than a five-region climate dropdown. Runs the same engine as the Manual J app, and tells you how precisely your ZIP matched.
Related app: Manual J load calculator
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Free online HVAC ductulator
CFM ↔ velocity ↔ friction-band sizing for round and rectangular, with a clear path to the full offline Duct Tools app for static pressure and Manual D schedules.
Related app: Ductulator & static pressure
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Live
A2L P/T chart & superheat calculator
Browser P/T lookup and superheat/subcooling for R-454B, R-32, and R-410A (bubble/dew where glide applies), with CTA into A2L Safe Charge for max charge and job history.
Related app: R-454B superheat & A2L max charge
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