About Home Systems Sizing
Home Systems Sizing builds free, vendor-neutral calculators for sizing home and garage equipment. We sell nothing. Our only job is to give you the right size and show our work.
Why we exist
Search "what size mini split do I need" and nearly every calculator on the first page belongs to a company that also sells you the unit. That's a conflict of interest baked into the tool — the easiest way to sell a bigger unit is to recommend one. We started Home Systems Sizing to do the opposite: an honest estimate, every factor visible, and a plain warning about the most expensive mistake homeowners make (buying too big).
Our method
Our estimates use a Manual-J-lite approach. We start from the standard cooling rule of thumb — about 20 BTU per square foot, the same basis behind DOE and ENERGY STAR room-air-conditioner sizing guidance — then apply adjustments for climate zone, insulation quality, sun exposure, ceiling height, and occupancy. The result is rounded up to a standard equipment size.
This is a planning estimate, not an engineering certification. A full Manual-J load calculation from a licensed contractor accounts for window-by-window heat gain, air infiltration, duct losses, and building orientation in a way no rule of thumb can. For a whole-home or permitted install, get one. Our tools are for the homeowner who wants to walk into that conversation already understanding the numbers.
How we stay free
When we link to a product, it's an affiliate link, and we may earn a commission on qualifying purchases at no cost to you. That funds the site. It never changes the size our calculator recommends, and we never fabricate prices, specs, or reviews. See our affiliate disclosure for the full policy.
Who we are
Home Systems Sizing is published by Cedarstone Ventures, which builds independent, useful web tools. We hold no inventory and represent no manufacturer. If a tool here saved you from buying the wrong size, it did its job.