This site is owned and operated by Zone Air.
Worksheet · About
A free, browser-based load calculator for ductless mini splits — no signup, no download, and the email step is optional.
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 for each room, and the optional emailed report breaks it down: envelope and infiltration, internal gains, windows, doors, ventilation, and duct losses. The load math runs in your browser and it never asks you to create an account.
Sizing is an easy step to get wrong, and the usual temptation is to go too big. ENERGY STAR notes that an oversized air conditioner short-cycles, removes less humidity, and takes more wear and tear — 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 is a simplified take on the ACCA Manual J 8th Edition residential load method — the framework professional load software uses and building codes reference. It is not ACCA-approved Manual J software. 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 typical default values for anything you don't specify. How it works walks through the method step by step.
Treat the result as a planning number, not 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 done in ACCA-approved software is still the right call, and the calculator carries a notice saying so.
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 load 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 (385) 487-3391, or email [email protected].
Mini Split Sizing Calculator · 4400 W 2000 S, Salt Lake City, UT 84104