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HVAC made simple
HVAC CALCULATOR
Furnace Replacement Savings Calculator
Compare your current gas furnace with a higher-efficiency replacement and estimate potential annual fuel savings, long-term savings, and simple payback.
1. Current Furnace
Tell us about the furnace currently heating your home.
%
If you know the rated AFUE of your existing furnace,
enter it here. Older furnaces may perform differently
from their original rating because of condition,
maintenance, and installation.
$
per year
Enter your estimated annual natural-gas cost attributable
to space heating, rather than your entire utility bill
if gas is also used for water heating, cooking, or
other appliances.
Why use annual heating cost?
Starting with your actual or estimated annual furnace fuel
cost makes the comparison more relevant to your home than
using a generic national heating-cost assumption.
2. Replacement Furnace
Enter the AFUE rating of the furnace you are considering.
%
Enter the rated AFUE of the replacement furnace.
Example Comparison
80% → 96% AFUE
The comparison assumes both furnaces are meeting the same useful annual heating demand. The higher-efficiency furnace therefore needs less fuel to deliver that useful heat.
Compare with:
3. Natural Gas Price
Enter your approximate delivered natural-gas rate.
$
per therm
Use your current utility rate when possible. One therm
represents approximately 100,000 BTUs of fuel energy.
Why do we ask for this?
The annual dollar savings calculation is based primarily on your entered annual heating cost. Your gas rate lets the calculator also estimate annual therm consumption and therms potentially saved.
4. Replacement Cost (Optional)
Enter your estimated net project cost if you want a simple payback estimate.
$
installed
Include equipment, labor, permits, and other project
costs as appropriate.
$
total
Enter only incentives you reasonably expect to qualify
for. Program eligibility and availability can change.
5. Annual Fuel Price Change (Optional)
Use this only if you want long-term projections to assume gas prices change each year.
% / yr
Leave this at 0% for a simple constant-price comparison.
Future utility prices are uncertain.
For a conservative comparison
Leaving fuel-price change at 0% avoids assuming that natural-gas prices will rise or fall in the future.
YOUR ESTIMATE
Estimated Furnace Replacement Savings
Based on the AFUE ratings and annual heating cost you entered.
Estimated Annual Fuel Savings
$0
Estimated first-year savings
Current Annual Cost
$0
Estimated New Annual Cost
$0
Estimated Annual Savings
$0
Estimated Fuel-Cost Reduction
0%
Furnace Efficiency Comparison
CURRENT FURNACE
80% AFUE
—
→
REPLACEMENT FURNACE
96% AFUE
—
Estimated Fuel Use
Current Furnace AFUE
—
Replacement Furnace AFUE
—
Current Estimated Gas Use
—
Replacement Estimated Gas Use
—
Estimated Therms Saved
—
Natural Gas Price Used
—
Potential Long-Term Fuel Savings
These projections assume the same heating demand each year and use the annual fuel-price change you entered. They do not include financing, maintenance, repairs, investment returns, or equipment replacement.
5-Year Savings
$0
10-Year Savings
$0
15-Year Savings
$0
20-Year Savings
$0
Net Replacement Cost
$0
Simple Fuel-Savings Payback
—
💡 How Is Furnace Replacement Savings Calculated?
Furnace Replacement Savings Formula
Useful annual heat index
Current fuel use × Current AFUE
New fuel requirement
Useful heat index ÷ New AFUE
New annual fuel cost
Current annual cost × (Current AFUE ÷ New AFUE)
Annual savings
Current cost − New estimated cost
Simple payback
Net replacement cost ÷ Annual fuel savings
🔥 A higher AFUE does not mean the same percentage reduction in your gas bill.
Moving from an 80% AFUE furnace to a 96% AFUE furnace does not mean that space-heating fuel cost automatically falls by 16%. For the same useful heating demand, the estimated fuel requirement is compared using the ratio of the old and new efficiencies. Other gas appliances and fixed utility charges are not affected by furnace AFUE.
Furnace Replacement Is About More Than Fuel Savings
AFUE-related fuel savings are only one part of a furnace replacement decision. Equipment condition, repair history, comfort, reliability, blower performance, staging or modulation, ductwork, installation quality, venting, home heat loss, fuel prices, warranty coverage, and the remaining life of the existing furnace can all matter.
Important:
This calculator provides an educational estimate and does
not guarantee actual energy or dollar savings. AFUE is a
standardized seasonal efficiency rating, while real-world
furnace performance and fuel consumption vary with climate,
weather, equipment condition, sizing, installation, duct
losses, thermostat settings, home insulation, air leakage,
maintenance, occupant behavior, utility rate structures,
and other factors. Annual heating cost should exclude
unrelated natural-gas consumption where possible. Rebates,
tax credits, and incentive programs have eligibility rules
and may change. Consult current program requirements,
utility rates, equipment specifications, and a qualified
HVAC professional when evaluating a furnace replacement.