Methodology

This page explains how the ClimateCalcs calculators are derived and verified — and why they need no ongoing maintenance to stay correct.

1. Timeless math, stable constants

Every tool computes from a closed-form building-science formula and stable physical / industry constants: 1 ton = 12,000 BTU/h, 1 kWh = 3,412 BTU, 1 therm = 100,000 BTU, propane 91,500 BTU/gal, heating oil 138,500 BTU/gal, natural gas ~1,037 BTU/cu ft, ~400 CFM/ton, and the ASHRAE 62.2 ventilation coefficients (0.03 and 7.5). Efficiency metrics cite the DOE 2023 SEER2/HSPF2 test basis. These values do not drift, so the statements stay true over time.

2. No prices, no feeds

There is deliberately no energy price, no equipment price database, no labor-rate table, no live rebate or tax-credit amount and no product catalog. Every cost tool works on the rates you enter from your own bills and quotes ($/kWh, $/therm, $/gal, $/ton, APR). That is why the site is correct regardless of what energy or equipment prices do.

3. Numeric self-check

Every formula is asserted against a worked example with known numbers (for instance: 1,500 sq ft × 25 BTU/sq ft = 37,500 BTU ≈ 3 tons; 36,000 BTU/h at COP 3 draws 3.52 kW; ASHRAE 62.2 for 2,000 sq ft / 3 bedrooms = 90 CFM; the dew point at 77 °F and 60% RH is 62 °F). A release gate runs all of these and fails on any mismatch, so "verification" here is mathematical correctness plus accurate constants — not a time-based check.

4. Rule-of-thumb vs a load calc

The climate-zone BTU-per-sq-ft bands are labeled rule-of-thumb estimates for a first-pass size. They are not a substitute for a professional Manual J / Manual S load calculation, which accounts for insulation, windows, orientation, infiltration and duct design. Oversizing hurts comfort, humidity control and efficiency, so we say plainly: get a load calc before you buy.