Calculator
HVAC Load Calculator
Run a Manual J-style load screening on site, enter home size, climate region, insulation, and internal heat gains to get recommended cooling and heating capacity in BTU/hr and tons. Free, no signup.
Free
Total square footageConditioned living space only, not garage or attic.
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.
Average ceiling height
2,000 sq ft · Zone 3 (Warm)
Recommended heating capacity
2.0 tons
18,563 BTU/hr
5.4 kW
- 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 load breakdown
- Envelope heating load18,113 BTU/hr
- Occupant heat loss offset450 BTU/hr
- Total18,563 BTU/hr
Manual J screening estimate (±10-15% for typical homes). Run a documented room-by-room Manual J before final equipment selection on replacements over 3 tons.
Quick reference
- 1 ton of cooling
- 12,000 BTU/hr
- 1 kW cooling
- 3,412 BTU/hr
- Typical home (2,000 sq ft)
- 2.5-4 ton central AC
- Occupant heat gain
- ~450 BTU/person
- Manual J screening
- ±10-15% typical home
What you'll get
Choose whole building or single room
Whole building runs a Manual J-style screening with envelope, design temps, and internal gains. Single room sizes one zone with a simpler field set.
Enter building or room details
Add square footage, climate region, insulation, windows, and, for whole homes, wall construction, foundation, and optional design temperatures.
Get equipment capacity
See calculated cooling and heating load, recommended tonnage, and a component breakdown you can use to validate contractor quotes.
How it works
- 1
Choose whole building or single room
Whole building runs a Manual J-style screening with envelope, design temps, and internal gains. Single room sizes one zone with a simpler field set.
- 2
Enter building or room details
Add square footage, climate region, insulation, windows, and, for whole homes, wall construction, foundation, and optional design temperatures.
- 3
Get equipment capacity
See calculated cooling and heating load, recommended tonnage, and a component breakdown you can use to validate contractor quotes.
Why HVAC contractors run load calculations on every replacement
Proper HVAC sizing starts with a load calculation. An undersized system cannot maintain comfort on design days; an oversized system short-cycles, wastes energy, and fails to dehumidify. This calculator gives you a Manual J-style screening estimate in the field, before you commit to equipment.
The model accounts for envelope load by climate zone, ceiling height, insulation, sun exposure, window type, occupant heat gain, equipment and lighting loads, and infiltration via air-tightness selection. For final equipment selection on large homes, follow up with a full ACCA Manual J room-by-room calculation.
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Load Calculator FAQs
The BTU Calculator is optimized for single-room and window-unit sizing. The HVAC Load Calculator defaults to whole-home inputs, adds equipment and lighting internal gains, air tightness, and sunroom/kitchen factors, closer to a contractor Manual J screening workflow.
No. This is a simplified screening estimate (±15-20%). A full ACCA Manual J includes room-by-room dimensions, duct location, orientation-specific solar gains, and latent loads. Use this for preliminary sizing and customer conversations; run Manual J software before final equipment purchase.
Results show BTU/hr, kilowatts (kW), and standard residential tonnage (1 ton = 12,000 BTU/hr). Heating output includes furnace-size rounding for common nameplate capacities.
Yes. Every tool on CloseCrew is free for HVAC contractors, no account required to run calculations.
Where to next
Watch the work before you hear from us
Diagnostics, installs and the odd bad attic, from contractors who film their own jobs.