BTU Calculator
Room-by-room heating and cooling load in BTU/h from area, climate zone and envelope.
BTU/h · Manual J
Size it once, size it right.
Load calculations, duct sizing, static pressure and running cost — the numbers an HVAC job actually turns on, as tools you can print.
Start here
all 15 toolsFurnace Size Calculator
Input BTU/h and output capacity from load, climate zone and AFUE.
BTU/h · AFUE
SEER2 Savings Calculator
Annual cooling cost and payback when you move from one SEER2 rating to another.
SEER2 · $/yr
HVAC Replacement Cost Calculator
Installed cost band by system type, tonnage and region, with the line items.
$ · installed
AC Unit Size Calculator
Tonnage for a whole house, with the oversizing check most rules of thumb skip.
tons · sq ft
Duct Size Calculator
Round and rectangular duct sizes from CFM and friction rate, with equivalent diameter.
CFM · in. w.c./100 ft
The order the work goes in
01
Calculate the load
Room by room, with your actual glass, insulation and design temperatures. Not square feet times a number someone remembered.
Manual J worksheet02
Measure what the duct can carry
Static pressure first, then the friction rate, then the sizes. A system that cannot move the air will not deliver the capacity you bought.
Static pressure calculator03
Price the running cost, not the rating
AFUE, SEER2 and HSPF2 are three different scales. Convert them all to dollars per delivered MMBtu and the comparison becomes arithmetic.
Fuel cost calculatorFour sections
Colour means temperature here, not decoration. Warm is the heating side, cool is the cooling side, and the two neutral sections are the ones that measure both.
Sizing & Load
5 tools, 4 guides
Manual J load, BTU/h, tonnage, duct sizing and static pressure — the numbers that decide what equipment goes in.
Heating
3 tools, 5 guides
Furnaces, heat pumps and the efficiency ratings that price them — AFUE, HSPF2 and the cold-climate question.
Cooling
3 tools, 5 guides
Air conditioners, mini splits, refrigerant and SEER2 — the cool side of the manifold.
Service & Costs
4 tools, 5 guides
Replacement cost, maintenance, filters and the credits that move the price — what the job costs and what keeps it running.
Guides worth the time
all 19 guidesHow to Size an AC Unit
Why square-foot rules of thumb oversize, and what to measure instead.
9 min read
Cold Climate Heat Pumps
Capacity at 5°F, balance points, and when a dual-fuel setup wins.
11 min read
SEER2 Explained
What changed in 2023, how SEER converts to SEER2, and the regional minimums.
9 min read
HVAC Replacement Cost
What a full system costs installed in 2026, and which line items move it.
11 min read
AC Not Cooling
Running but not cold, frozen coil, compressor silent — a decision list.
12 min read
HVAC Tax Credits in 2026
25C, the heat-pump caps, and what the 2025 law changed about the deadline.
9 min read
Keep the system sized right.
40 pages, 15 calculators, and every regulatory figure on the site read from its primary source and stamped with the date. No accounts, no sign-up, nothing stored.