How we size heat pumps and source rebate data

Our calculator outputs a BTU range and product recommendations. Our rebate guides describe state, federal, and utility programs by name and dollar amount. Both depend on assumptions and sources you have the right to scrutinize. This page explains exactly how we do the math, where we get the data, and where the limits are.

How the calculator sizes

We size heat pumps using a simplified Manual J Load Calculation framework — the industry-standard residential HVAC sizing methodology published by the Air Conditioning Contractors of America (ACCA). The calculator is a guide, not a replacement for a professional Manual J on whole-home installations.

Inputs we use

• Square footage — the conditioned area being heated or cooled
• Climate zone — IECC zone 1–7 (we look up from ZIP)
• Insulation tier — poor / average / good (R-value bands)
• Sun exposure — low / med / high (orientation + windows)
• Ceiling height — adjustment factor above 8ft standard

The formula

Base BTU = sqft × climate-zone factor (20–35 BTU/sqft). Insulation, sun, and ceiling adjustments multiply that base. We round up to the nearest standard mini split BTU class (9k, 12k, 18k, 24k, 36k) and show a range to acknowledge real-world variability.

What we don't model

• Air infiltration (blower door results)
• Detailed window-by-window solar gain
• Multi-zone load distribution (multi-zone sizing recommends a Manual J)
• Ductwork losses (we assume ductless mini splits)

How we source rebate data

Every rebate page draws from primary sources — state energy office sites, utility program pages, IRS guidance — and lists those sources at the bottom of the page with last-verified dates. We do not cite retailer blogs or competitor sites as sources.

Confidence levels

• Verified — the source confirms current status as of the last-verified date
• Verification pending — source under review; treat the figure as approximate
• Preliminary — program announced but not yet operational; eligibility may not exist when you apply

Refresh cadence

• State pages — re-verified quarterly
• Federal context — every 6 months or on any IRS/IRA announcement
• Pages older than 180 days carry a "may be outdated" banner until refreshed

Affiliate disclosure

Some of our product links to Amazon are affiliate links — if you click through and buy, we earn a small commission at no extra cost to you. We pick products based on a fit-for-the-job standard (sizing, climate suitability, rebate eligibility) and not commission rates. See our full affiliate disclosure.

What we are not

We are not a licensed HVAC contractor, tax advisor, or energy auditor. Our calculator is a guide. Our rebate summaries describe programs but cannot guarantee eligibility — that depends on your specific situation, the program's current funding status, and (often) your installer. For purchases above $5,000 we recommend confirming eligibility directly with the program before placing the order.

How we update this page

This methodology page is itself sourced and dated. Changes to our sizing formula, source standards, or refresh cadence get reflected here. If you find a factual error in any guide on this site, we want to hear about it — email hello@splitsizer.com.