Worksheet · About
A free, browser-based load calculator for ductless mini splits — no signup, no email, no download.
What This Is
This site does one thing: it tells you what size ductless mini split a room — or a whole home — actually needs. You enter a ZIP code and a room, and the calculator returns a BTU/h load with the full breakdown behind it: envelope and infiltration, internal gains, windows, doors, ventilation, and duct losses. It runs entirely in your browser and never asks you to create an account.
Sizing is the step most DIY installs get wrong, and almost always in the same direction: too big. An oversized mini split short-cycles, never dehumidifies properly, and wears out early — so a real load number, not a square-footage rule of thumb, is the single most useful thing to have before you buy anything.
Where the Math Comes From
The calculation follows the ACCA Manual J 8th Edition residential load methodology — the same framework professional load software uses and building codes reference. Your ZIP code resolves the outdoor design temperature, altitude, and latitude; the room inputs feed conduction, solar gain, infiltration, and ventilation terms; and Basic mode fills in Manual J default values for anything you don't specify. How it works walks through the method step by step.
For most residential rooms the result lands within 10–15% of a paid in-home assessment. It is a planning number, not a stamped design: for whole-home replacements, heavily glazed great rooms, or mixed construction, a professional Manual J from an ACCA-certified contractor is still the right call, and the calculator will tell you so rather than pretend otherwise.
Why It's Free
When the calculator finds systems whose capacity matches your load, it links to DIY mini splits sold by Zone Air — pre-charged systems designed for self-install. That's what keeps the calculator free. The load calculation itself doesn't bend toward the catalog: the BTU number comes out of the Manual J math whether or not any product matches it, and when your load needs something the catalog doesn't cover, it says so.
Questions about sizing itself? Start with the sizing FAQ.
Contact
Questions about your sizing result, or about a system the calculator matched? Send a message and the support team will reply by email.
Prefer the phone? Call (801) 882-2324.
Mini Split Sizing Calculator · 4375 W 1980 S, Unit D, Salt Lake City, UT 84104