Sources & formulas

Every calculator on ClimateCalcs rests on established math from thermodynamics, psychrometrics and building science. Unlike topics with a time dependency, "verification" here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.

Capacity & airflow

• Cooling capacity: 1 ton = 12,000 BTU/h; 1 kW = 3,412 BTU/h.
• Airflow: ~400 CFM per ton of cooling (350–450 CFM/ton in practice).
• Rule-of-thumb sizing: cooling/heating BTU ≈ floor area × a climate-zone BTU/sq-ft band (labeled estimate) × adjustments (sun, occupancy, kitchen, ceiling height). A first-pass estimate, not a Manual J.

Efficiency

• DOE 2023 basis: SEER2 and HSPF2 are the DOE 2023 seasonal test metrics; EER and COP are single-point metrics.
• Documented approximations: SEER ≈ EER ÷ 0.9; HSPF ≈ COP × 3.412 — estimates, not identities.
• AFUE: annual fuel utilization efficiency; furnace fuel = output ÷ (AFUE × energy content).

Fuel energy content ($/MMBTU)

• 1 therm = 100,000 BTU; 1 kWh = 3,412 BTU; propane ≈ 91,500 BTU/gal; heating oil (#2) ≈ 138,500 BTU/gal; natural gas ≈ 1,037 BTU/cu ft.
• Delivered cost: $/MMBTU = your price ÷ (energy content × efficiency) × 1,000,000.

Comfort & ventilation

• ASHRAE 62.2: whole-house ventilation CFM = 0.03 × floor area + 7.5 × (bedrooms + 1).
• Air changes: ACH = CFM × 60 ÷ room volume (ft³).
• Psychrometrics: dew point via the Magnus formula; heat index via the NWS Rothfusz regression.

Cost tools

• Every cost tool uses the rate you enter ($/kWh, $/therm, $/gal, $/ton, APR) — no energy price, equipment price or rebate amount is stored, so the site needs no maintenance.
• Financing: standard amortization M = P·r ÷ (1 − (1+r)⁻ⁿ), illustrative only, not a loan offer.

Tax credits (IRA 25C / ENERGY STAR / DSIRE) are named in the guides only; amounts and eligibility change — confirm current details with the IRS and ENERGY STAR.