Compare boiler and furnace quotes using your heating bill, efficiency ratings, upkeep costs, and the number of years you expect to own the system.
Advanced options
Table of contents
How to use our Boiler vs Furnace Lifetime Cost Calculator
- Enter the space-heating part of 12 months of fuel bills in Current annual heating fuel cost. Leave out fixed customer charges and fuel used for water heating, cooking, or clothes drying.
- Enter Current heating system AFUE, Boiler AFUE, and Furnace AFUE from equipment labels, quotes, or specification sheets.
- Enter each installed quote and annual maintenance budget. Include required ductwork, piping, radiators, venting, permits, and electrical work in the matching installed cost.
- Set Years to compare to the time you expect to own the home or equipment. Open Advanced options only if you want to include discounting, fuel-price changes, or option-specific fixed charges.
- Click Calculate. Check that the lower-cost option matches the signed Boiler cost minus furnace cost: a positive amount means the furnace costs less, while a negative amount means the boiler costs less.
Definitions
AFUE: Annual Fuel Utilization Efficiency. It is the percent of a fuel's energy that the heating equipment turns into useful heat over a typical year. Higher AFUE generally means lower fuel use for the same heating need. [2]
Current annual heating fuel cost: The yearly quantity-based fuel cost for space heating only. It does not include fixed account charges or fuel used by other appliances.
Installed cost: The one-time cost of equipment, labor, permits, and required conversion work after confirmed rebates or credits.
Fixed service charge: An annual account or service fee that applies only if that heating option is chosen, rather than a charge based on fuel quantity.
Discount rate: A planning rate that converts future expenses into their value in today's dollars.
Lifetime cost: Installed cost plus the calculated cost of fuel, maintenance, and option-specific fixed charges during the selected years.
Common mistakes and quick fixes
Mistake: Current annual heating fuel cost includes gas or fuel used by a water heater, stove, or dryer.
Fix: Enter only the quantity-based space-heating portion in Current annual heating fuel cost.
Mistake: Boiler installed cost or Furnace installed cost leaves out ducts, piping, venting, permits, or electrical work.
Fix: Use complete installed quotes and include all conversion work in the matching installed cost.
Mistake: Boiler AFUE or Furnace AFUE is guessed from a similar model.
Fix: Copy the rated AFUE from the exact quoted equipment specification or label.
Mistake: Years to compare is treated as a promised equipment life.
Fix: Set Years to compare to your own ownership or planning period, then test a longer or shorter period if needed.
Mistake: Boiler fixed service charge or Furnace fixed service charge includes a utility customer fee that continues regardless of the system chosen.
Fix: Enter only charges caused by that option, and use 0 for charges that remain either way.
Limitations & Key Assumptions / Boundary Conditions
- This is a planning estimate for options that use the same fuel-price basis. Do not use it to compare systems using different fuels unless the entered annual heating fuel cost has been converted to a matching basis.
- The annual heating bill is assumed to reflect similar weather, thermostat settings, and heating demand in future years. Changes to insulation, additions, occupancy, or indoor temperature can change actual costs.
- Maintenance and fixed charges stay level in the calculation unless you change the entered values. Repairs, replacement parts, financing, taxes, insurance, and resale value are not included.
- The calculator does not size equipment or judge comfort, duct condition, piping condition, airflow, radiator output, humidity, or installation quality.
- Years to compare is an ownership planning period, not a prediction that either system will last that long. The editable 15-year starting value is a US planning reference. [1]
- A negative Boiler cost minus furnace cost means the boiler is estimated to cost less. It is not an error.
Methodology
How the fuel estimate works
The calculator starts with the useful heat implied by your current annual heating bill. It adjusts that bill by the current system's AFUE and the AFUE of each proposed system. AFUE entries use the same percent scale, so the percent values cancel in the ratio.
boiler fuel in year 1 = current annual heating fuel cost x (current AFUE / boiler AFUE)
furnace fuel in year 1 = current annual heating fuel cost x (current AFUE / furnace AFUE)
Recurring costs and lifetime totals
For each year, fuel cost changes by the Annual fuel cost change rate. Maintenance and the option-specific fixed service charge are added for that year. If an Annual discount rate is entered, each future year's recurring cost is converted to present dollars. N is Years to compare, g is annual fuel cost change as a decimal, and d is annual discount rate as a decimal.
present value of recurring costs = Sum(t=1 to N) [(fuel in year 1 x (1 + g)^(t - 1) + maintenance + fixed charge) / (1 + d)^t]
lifetime cost = installed cost + present value of recurring costs
Boiler cost minus furnace cost = boiler lifetime cost - furnace lifetime cost
Worked example
With a $1,500 current heating bill, 80% current AFUE, 90% boiler AFUE, and 95% furnace AFUE, first-year fuel cost is about $1,333.33 for the boiler and $1,263.16 for the furnace. Using the example installed costs, maintenance budgets, 15 years, and zero discounting or fuel-cost change, the boiler lifetime cost is $35,750.00 and the furnace lifetime cost is about $30,647.37. The signed difference is about $5,102.63, so the furnace costs less in this example.
Calculation choices
Installed costs are counted at the start of the comparison and are not discounted. The lower-cost option is chosen from unrounded totals, so a decision can remain different even when rounded dollar totals look the same.