What size system do you need?
A transparent Manual-J-lite estimate for Front Range homes — then book Colorado Bear for a real on-site load calculation before you buy.
Manual-J lite
HVAC Size Calculator
Enter square footage, climate, and insulation. This is a starting estimate — not a substitute for an on-site Manual-J load calculation.
Castle Rock & the Front Range typically use Cold.
Excellent = modern sealed envelope. Poor = older single-pane with thin attic insulation.
Approximate starting point
2.5 tons
Cooling ≈ 32,400 BTU/hr
~80k BTU furnace
Heating load ≈ 69,300 BTU/hr output, rounded up to the nearest common furnace size.
These are rule-of-thumb estimates — not a substitute for a Manual-J load calculation. A Colorado Bear technician confirms the real number on-site with ductwork, orientation, windows, and infiltration.
How we got there
- Base load
- 1,800 sqft × 20 BTU/sqft = 36,000 BTU/hr
- Climate
- × 0.90 (cold)
- Insulation
- × 1.00 (average)
- Total
- 32,400 BTU/hr ÷ 12,000 = 2.70 tons
- Rounded
- Nearest 0.5 ton → 2.5 tons (estimated)
- Heating
- 1,800 sqft × 35 BTU/sqft (adjusted) ≈ 69,300 BTU/hr → ~80k furnace
Why square footage alone isn’t enough
Elevation, window orientation, duct leakage, and how your home is used all change the real load. This tool uses the same homeowner-facing rule of thumb as ENERGY STAR–style guides (20 BTU/sqft × climate × insulation). Use it to get oriented — then schedule a free Manual-J visit so we size the equipment once, correctly.
Get a real Manual-J — on us.
Skip the guesswork. A Colorado Bear technician will measure your home and recommend the right tonnage before you commit to equipment.
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