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HVAC BTU Sizing Calculator

Square footage + climate → BTU/hr and AC tons needed per Manual J simplified.

Where this fits

📦 Business & Seller OpsGoing 1099FreelancersFounders

This tool lives inside Going 1099 and is most useful for freelancers and founders.

Corp Tax Rate21%
SE Threshold$400
FICA Cap 2024$168,600

Space Details

Recommended AC
4 tons
42,788 BTU/hr
Cooling load
42,788 BTU
before rounding to half-ton
Heating estimate
51,345 BTU
heat load varies by climate
Load per sq ft
28.1 BTU
per sq ft/hr
1

Base cooling load

baseBTU/sqft = climate lookup

= 25 BTU/sq ft/hr (moderate climate)

ACCA Manual J simplified — full Manual J requires room-by-room calc

2

Adjustments

adjusted = base × insulationFactor × windowFactor × heightFactor

= 28.1 BTU/sq ft/hr

Insulation: ×average, Windows: ×average (10-20%), Ceiling: 9 ft

3

Cooling BTU

coolingBTU = sqFt × adjustedBTU/sqFt + occupant load

= 1,500 × 28.1 + 600

= 42,788 BTU/hr

600 BTU added per occupant beyond 2

4

Cooling tons

tons = BTU/hr ÷ 12,000

= 3.57 tons → recommended: 4 tons

1 ton of AC = 12,000 BTU/hr

5

Heating BTU

= 51,345 BTU/hr

Heating load estimate — heating system sizing varies significantly by climate

Key insight

This is a simplified Manual J estimate. For a permit-ready equipment specification, use a full Manual J calculation. Rule of thumb: 1 ton per 400–600 sq ft works for average construction in a moderate climate. Oversizing an AC unit causes short cycling and poor humidity control.

Use this result in →

🏠Insulation R-Value Guide

#ShowYourWork

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