Furnace Sizing Calculator for Minnesota Climate Zones
Estimate the required furnace output (BTU/hr) for your Minnesota home based on square footage, insulation quality, ceiling height, windows, and your specific climate zone. Uses Manual J simplified load calculation methodology.
Formulas Used
Manual J Simplified Heat Load Calculation (ACCA Manual J, 8th Edition):
Total Heat Loss:
Qtotal = Qwalls + Qceiling + Qwindows + Qdoors + Qfloor + Qinfiltration
Conduction Loss (walls, ceiling, windows, doors):
Q = U × A × ΔT
Where: U = thermal transmittance (BTU/hr·ft²·°F), A = area (ft²), ΔT = Tindoor − Toutdoor design (°F)
Infiltration Loss:
Qinf = 0.018 × ACH × V × ΔT
Where: 0.018 = specific heat of air (BTU/ft³·°F), ACH = air changes per hour (natural), V = conditioned volume (ft³)
Slab Floor Loss:
Qslab = F2 × P × ΔT
Where: F2 = 0.73 BTU/hr·ft·°F (MN insulated slab edge), P = perimeter (ft)
Design Furnace Output:
Qdesign = Qtotal × 1.25 (ACCA Manual S oversizing factor for extreme cold climates)
Rounded up to nearest 10,000 BTU/hr standard furnace increment
Furnace Input Capacity:
Qinput = Qoutput / AFUE = Qoutput / 0.96