How the sizing screen works and where claims come from

Five broad inputs produce a rounded shopping range. Missing building and equipment details keep that range from being a load calculation. Each regulatory, rebate, and disclosure claim below carries its own source, status, jurisdiction, and review date.

The exact sizing formula

Square footage × 20 BTU/hour is the base. The accepted area is 50–6,000 square feet. Four manually selected factors then adjust the base:

Climate means warm, mixed, or cold. Insulation means poor, average, or excellent. There is no ZIP lookup in this version; the climate band is selected by the reader.

The lower and upper display values are 8% below and 8% above the adjusted result, each rounded to the nearest 100 BTU. The comparison class is the first class at or above the unrounded result: 6k, 9k, 12k, 18k, 24k, 30k, 36k, 48k BTU. Results above the largest class return no comparison class and require professional or multi-zone design; 48k is not used as a false cap.

The screening boundary

The displayed band communicates a display convention, not measured accuracy. No validation percentage against completed Manual J projects is claimed. ACCA Manual J is the ANSI-recognized residential load procedure for producing final equipment-sizing loads.

A final design still needs details that the five inputs do not collect:

• local winter and summer design temperatures;
• air leakage, ventilation, occupancy, and internal loads;
• window-by-window orientation, area, and solar gain;
• room-by-room distribution and any duct losses;
• the exact matched system's minimum output and capacity at design temperature.

One enclosed room can use the result to compare likely size classes. Whole-home, multi-zone, cold-climate, and permit-sensitive work needs a project-specific load calculation and model data before equipment is selected.

The rebate boundary

A federal tax credit and a state-administered rebate are different programs. The federal Energy Efficient Home Improvement Credit applies only to qualifying improvements placed in service through December 31, 2025. Federal Home Energy Rebate funding, by contrast, is available only through participating state, territory, or Tribal programs. A federal program page does not establish that money is open for a particular household today.

Check the named administrator close to purchase for current funding, income rules, eligible matched equipment, contractor requirements, reservation order, and stacking limits. A published maximum is not a promise of eligibility.

Public evidence ledger

One record covers one public claim. Verified means the named source supports the wording. Unknown at this scope means a national source cannot answer the local question. Primary-source conflict means official or first-party sources disagree. Freshness is calculated separately, so a newly checked conflict never becomes “verified” merely because it is recent. External sources use class-specific recheck windows. Claims about the current calculator method are checked against the implementation during test validation, so calendar age alone does not label them “Recheck due.”

Ledger schema: v1.0.0. All dates use YYYY-MM-DD in the underlying record.

Affiliate links

Amazon product links may earn a commission at no extra cost to the buyer. The commission relationship belongs beside the recommendation or link, not only on a separate legal page. See the full affiliate disclosure for the revenue relationship and recommendation boundary.

Limits and corrections

Sizing screens are not contractor designs. Rebate summaries are not eligibility guarantees or tax advice. Regulatory summaries are not a substitute for the responsible agency, local authority, or qualified professional. Confirm material requirements before signing a quote or buying equipment.

Found a factual error or a changed source? Email hello@splitsizer.com with the page, claim ID, and primary source.