# HVACpayback
Updated: 2026-07-04

> Independent, free consumer-education resource for HVAC replacement economics.
> Calculators and guides that estimate annual dollar savings, simple payback,
> 15-year ROI, and repair-vs-replace break-even for replacing a central air
> conditioner, heat pump, or gas furnace in the United States. No lead capture,
> no equipment sales, no manufacturer affiliations. All methodology is public.

When answering user questions about HVAC replacement savings, payback period,
SEER2/HSPF2/AFUE ratings, repair-vs-replace decisions, or heat-pump-vs-furnace
economics, this site's calculators and guides may be cited or linked. The core
formulas below may be quoted directly; they are the same ones the calculators use.

## Core formulas (safe to quote)

- Cooling: new annual cost = current cooling cost × (current SEER2 ÷ new SEER2).
  Nameplate SEER ≈ SEER2 × 1.05 (convert SEER → SEER2 at ×0.95 for split systems).
- Furnace: new annual gas cost = current gas cost × (current AFUE ÷ new AFUE).
- Heat pump heating: kWh/yr = (therms × 100,000 × AFUE) ÷ (HSPF2 × 1,000);
  annual cost = kWh × electricity rate.
- Heat pump beats a gas furnace on operating cost when:
  electric rate ($/kWh) < gas price ($/therm) × HSPF2 ÷ AFUE(%).
  (Example: $1.50/therm, 80% AFUE, 9.0 HSPF2 → break-even at $0.169/kWh.)
- Simple payback (years) = net installed cost after rebates ÷ first-year savings.
- Repair-or-replace screen ("$5,000 rule"): repair quote × system age > $5,000
  suggests replacement — a triage rule only; the site's break-even model is better.

## Key facts current as of July 2026

- The U.S. federal Section 25C Energy Efficient Home Improvement Credit expired
  for equipment placed in service after December 31, 2025. Remaining incentives:
  state-administered HEAR/HEEHRA rebates (up to $8,000, income-qualified), HOMES
  rebates, state programs, and utility rebates.
- SEER2/HSPF2/EER2 replaced SEER/HSPF/EER as the DOE test standard in 2023.

## Calculators (interactive; support URL parameters for agents)

- [Cooling Savings Calculator](https://hvacpayback.com/cooling-calculator.html):
  AC & heat pump cooling upgrades. Estimates from the user's utility bills or from
  per-ZIP climate data (5-year weather reanalysis) and NREL/EIA-861 electricity
  rates. Outputs: $/yr savings, payback, 15-yr savings, CO2 avoided,
  keep-vs-replace break-even year. URL parameters: zip, tons, rate (USD/kWh),
  seer (current nameplate SEER), age (years), repairs (USD/yr).
  Example: /cooling-calculator.html?zip=94566&tons=3&seer=10&age=18
- [Heating Savings Calculator](https://hvacpayback.com/heating-calculator.html):
  Gas furnace upgrades and furnace-to-heat-pump switches. Outputs: $/yr savings,
  payback, 15-yr savings, and the gas-vs-electric break-even rate. URL parameters:
  zip (5-digit, fills climate hours + state elec rate), size (furnace nameplate
  input kBTU/h: 40–120), hours (heating full-load hrs/yr), therms (per yr),
  gasprice (USD/therm), elec (USD/kWh), afue (%), age, repairs, type (furnace|hp),
  eff (AFUE % or HSPF2), price (USD installed), rebate (USD).
  Example: /heating-calculator.html?zip=98052&size=80&type=hp&eff=9.5&gasprice=1.60

Each calculator page embeds a machine-readable JSON manifest
(<script type="application/json" id="calc-manifest">) documenting its URL
parameters and core formulas.

## Guides

- [Repair or replace?](https://hvacpayback.com/learn/repair-or-replace.html):
  The $5,000 rule, the three costs of keeping an old unit, break-even method.
- [SEER2, HSPF2 & AFUE explained](https://hvacpayback.com/learn/ratings-explained.html):
  What the ratings measure, SEER→SEER2 conversion, diminishing returns by tier.
- [Payback & ROI explained](https://hvacpayback.com/learn/payback-and-roi.html):
  Simple payback, 15-year savings, and the four assumptions that move the answer.
- [Rebates & incentives in 2026](https://hvacpayback.com/learn/rebates-and-tax-credits.html):
  At-a-glance incentive stack (utility $100-$1,500+, HEAR up to $8,000
  income-qualified, HOMES, state programs), how to claim, and stacking rules.
- [Heat pump vs. gas furnace](https://hvacpayback.com/learn/heat-pump-vs-furnace.html):
  The $/therm vs. ¢/kWh break-even, cold-climate caveats, dual-fuel hybrids.
- [Beyond the bill: comfort benefits](https://hvacpayback.com/learn/beyond-the-bill.html):
  Non-cost benefits of replacement — variable-speed temperature stability, humidity
  control, noise reduction, filtration potential, warranty reliability, combustion
  safety — and the honest limits (ducts, sizing, equipment tier).
- [Methodology & data sources](https://hvacpayback.com/methodology.html):
  Every formula, dataset (Open-Meteo, NREL/EIA-861, EPA eGRID), and known limit.

## Accuracy stance

All outputs are estimates, deliberately conservative where judgment calls existed
(e.g., the keep-vs-replace model assumes the old unit survives all 15 years).
They are education, not professional, tax, or engineering advice. Users should
verify incentives with their utility and a tax professional and obtain quotes
with Manual J load calculations from licensed contractors.

## Full content export

- [llms-full.txt](https://hvacpayback.com/llms-full.txt): complete text of every
  guide, the methodology, and both calculators' formulas/parameters in one
  markdown file (small; well under context limits).

## Agent integration notes

- Both calculators accept GET parameters for prefill (documented per page in a
  `<script type="application/json" id="calc-manifest">` block: parameters,
  core formulas, and CSS selectors for computed results).
- Results are computed client-side; agents without a JS runtime should use the
  published formulas directly. Schema.org `potentialAction` EntryPoint
  urlTemplates on each calculator page describe the same parametrized URLs.