FurnaceTallyInput BTU, output BTU, and the gap nobody explains.

FurnaceTally

Input BTU, output BTU, and the gap nobody explains.

SectionsLatest
Furnace BTU SizingInput against output, and how much of the label you actually get.4350
AFUE & EfficiencyWhat 80% and 96% mean on a bill, and when the upgrade pays back.5
Venting & Combustion AirCategory I against Category IV, vent sizing, and why a high-efficiency swap changes the chimney.5
Fuel & Running CostGas, propane and electric compared per delivered BTU rather than per unit.5
Replacement CostFurnace, install, and the venting work that turns a quote into a project.1204
  1. What Size Furnace — BTU Per Square Foot, and Why Input Is Not OutputFurnace BTU Sizing · 3 min read

    A 100,000 BTU furnace at 80% AFUE delivers 80,000. Sizing against the wrong one of those two numbers is a 25% error before anything else goes wrong.

  2. AFUE — What 80% and 96% Actually Cost to RunAFUE & Efficiency · 3 min read

    The percentage is easy. The payback calculation is the part that decides, and it is local.

  3. Furnace Venting — Why an 80% Uses Metal and a 96% Uses PlasticVenting & Combustion Air · 3 min read

    The pipe leaving the furnace is not an accessory. It is a consequence of how much heat the furnace took out of the exhaust.

  4. Comparing Heating Fuels — Put Them All in Dollars Per Million BTUFuel & Running Cost · 4 min read

    A therm, a gallon and a kilowatt-hour are not comparable until efficiency is applied to each of them.

  5. What a Furnace Replacement Quote Is Made OfReplacement Cost · 3 min read

    Two quotes on the same basement can differ by thousands, and the difference is usually the venting.

  6. Temperature Rise — The Nameplate Number That Says Whether It Was Set Up RightAFUE & Efficiency · 3 min read

    There is a range printed on the furnace, and a thermometer will tell you whether the installation is inside it.

  7. Single-Stage, Two-Stage, Modulating — What Longer Burns BuyFurnace BTU Sizing · 3 min read

    Most of the discomfort blamed on a furnace comes from how it delivers heat, not from how much it has.

  8. Five Signs the Furnace Is Too Big for the HouseFurnace BTU Sizing · 3 min read

    The furnace heats the house quickly and then stops. That is the complaint, even though it sounds like a compliment.

  9. Repair or Replace a Furnace — And the One Fault That Ends the DiscussionReplacement Cost · 3 min read

    Most furnace repairs are worth doing. One diagnosis is not a repair decision at all.

  10. Where the Vent Comes Out — Clearances That Cause Real FailuresVenting & Combustion Air · 3 min read

    A condensing furnace vents out the side of the house, and where that pipe ends is a code question with practical consequences every winter.

  11. Heating Degree Days — How to Tell a Cold Winter From a Broken FurnaceFuel & Running Cost · 3 min read

    The bill went up. Whether that means the winter was colder or the furnace got worse is a division problem.

  12. The Condensate Drain — A Small Pipe That Shuts Down the FurnaceVenting & Combustion Air · 3 min read

    The highest-efficiency furnaces are stopped most often by the least sophisticated part of them.

  13. The Orphaned Water Heater — What Happens to the Chimney After the Furnace LeavesVenting & Combustion Air · 3 min read

    The chimney was sized for two appliances. Take one away and the other one has a problem nobody mentioned in the quote.

Furnace BTU by area, climate and AFUE

360 calculations · Furnace BTU Sizing · browse all

Furnace size by city

3,984 calculations · Furnace BTU Sizing · browse all

Furnace replacement cost by city

996 calculations · Replacement Cost · browse all