Calculator
HVAC BTU Calculator
Size room heating and cooling loads in the field, enter square footage, climate zone, insulation, ceiling height, windows, and sun exposure to get recommended BTU/hr and tonnage for AC and heating. Free, no signup.
Free
Floor area
TexasZone 3 (Warm)Location · Texas · Zone 3, WarmYour state sets the IECC climate zone automatically.Summer (1% design): 102°F · Winter (99% design): 18°FDallas, Phoenix, Atlanta, MemphisHeating season (Nov-Mar), furnace and heat-pump heat loads are the priority.Pre-filled design temps match your state. Change them if your site runs hotter or colder than the state default, whole-building loads use them to fine-tune heating and cooling.
Ceiling height
300 sq ft · Zone 3 (Warm)
Heating
1.0 ton
11,820 BTU/hr
- Gas furnace / boiler40,000 BTU/hr
How we calculated this
- Gas furnace / boiler: 40,000 BTU/hr input capacity (check AFUE for delivered BTU).
Heating
- Base heating load9,975 BTU/hr
- Occupant heat loss offset225 BTU/hr
- Window heat loss1,920 BTU/hr
- Room-type adjustment-300 BTU/hr
- Total11,820 BTU/hr
This is a planning estimate (±15-20%). For central systems over 3 tons, run a full Manual J load calculation before purchase.
Quick reference
- 1 ton of cooling
- 12,000 BTU/hr
- Typical bedroom (300 sq ft)
- 6,000-9,000 BTU
- Typical whole home (2,000 sq ft)
- 2.5-4 ton central AC
- Occupant heat gain
- ~450 BTU/person
What you'll get
Enter room dimensions
Add square footage (or length × width), ceiling height, and choose room type, bedroom, living area, kitchen, sunroom, or garage.
Set climate and envelope
Pick your state or climate zone, insulation quality, exterior wall exposure, window type, and sun exposure for accurate load adjustment.
Get BTU and tonnage
See recommended cooling and heating BTU/hr, tonnage for equipment selection, and seasonal sizing notes for your climate.
How it works
- 1
Enter room dimensions
Add square footage (or length × width), ceiling height, and choose room type, bedroom, living area, kitchen, sunroom, or garage.
- 2
Set climate and envelope
Pick your state or climate zone, insulation quality, exterior wall exposure, window type, and sun exposure for accurate load adjustment.
- 3
Get BTU and tonnage
See recommended cooling and heating BTU/hr, tonnage for equipment selection, and seasonal sizing notes for your climate.
Why HVAC contractors use a BTU calculator before quoting equipment
Wrong equipment size is the root cause of comfort complaints, callback warranty work, and lost margin on change orders. An oversized AC short-cycles and fails to dehumidify; an undersized unit cannot maintain setpoint on design days. Field BTU screening before you quote gives customers confidence and protects your install margin.
This calculator adjusts base load by climate zone, insulation, ceiling height, window area and type, sun exposure, and room function, the same factors that drive ACCA Manual J room loads. For whole-home replacement sizing with internal gains and air tightness, use the HVAC Load Calculator. For duct runs after you know CFM, use the Duct Size Calculator.
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BTU Calculator FAQs
Rule-of-thumb ranges from 25-35 BTU/hr per sq ft in moderate climates to 40-50+ in hot-humid or cold regions, but insulation, ceiling height, windows, and sun exposure change the number significantly. Enter your actual room details rather than using a flat multiplier.
Divide BTU/hr by 12,000. A 24,000 BTU/hr load equals 2 tons. Residential equipment is sold in half-ton increments (1.5, 2, 2.5, 3, etc.). Always round up to the next standard size when between increments.
The BTU Calculator is optimized for single-room and zone sizing with a streamlined field workflow. The HVAC Load Calculator adds whole-building scope, internal heat gains, air tightness, and Manual J-style screening for full system replacements.
Yes. Every tool on CloseCrew is free for HVAC contractors, no account required to run calculations.
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