Sources & references
What we relied on and how. Accessed/reviewed October 2026.
- ACCA — Manual J – Residential Load Calculation
What we use it for: The recognized residential load-calculation methodology. Our calculator is simpler and is not Manual J.
Accessed October 2026 - ACCA — Manual S – Residential Equipment Selection
What we use it for: Equipment selection based on a proper design load; educational background on the methodology page only.
Accessed October 2026 - ENERGY STAR — HVAC Quality Installation
What we use it for: Advice that equipment be sized from the home's actual characteristics, not rules of thumb.
Accessed October 2026 - ENERGY STAR — Furnaces – Key Product Criteria
What we use it for: AFUE as the share of fuel turned into useful heat; efficiency levels of certified furnaces.
Accessed October 2026 - U.S. Department of Energy – FEMP — Purchasing Energy-Efficient Residential Furnaces
What we use it for: AFUE defined as seasonal useful output vs. fuel input; efficiency requirements.
Accessed October 2026 - ENERGY STAR — Seal and Insulate
What we use it for: That insulation affects heat loss. Not the source of our multiplier values.
Accessed October 2026 - ENERGY STAR — Why Seal and Insulate?
What we use it for: That air leakage affects heating energy. Not the source of our multiplier values.
Accessed October 2026 - Angi — How Much Does a New Furnace Cost?
What we use it for: 2026 installed-cost ranges by furnace type: electric $2,000–$7,000, gas $3,800–$10,000, oil $6,750–$10,000, propane $3,700–$14,200.
Accessed October 2026 · Data year 2026 · Site blocks automated link checks - This Old House — How Much Does a Furnace Cost? (2026 Pricing)
What we use it for: Cross-check: overall $1,600–$10,000 (avg ≈ $4,799); electric $2,000–$7,000, gas $3,800–$10,000, oil $6,750–$10,000.
Accessed October 2026 · Data year April 2026 - Modernize — 2026 Furnace Replacement Cost Guide
What we use it for: Cross-check: typical replacement ≈ $4,000–$10,000; gas $3,800–$10,000, electric $2,000–$7,000, oil ≈ $4,500–$9,000.
Accessed October 2026 · Data year August 2026 · Site blocks automated link checks - U.S. EPA — Carbon Monoxide's Impact on Indoor Air Quality
What we use it for: Safety context: combustion appliances should be professionally installed and maintained.
Accessed October 2026
Listing a source does not mean it endorses FurnaceCalculator.com. Coefficients that are our own assumptions rather than published values are labeled on the methodology page.