Free BTU Calculator

Basic Information

Tell us about your home

Square Footage * i

Total conditioned (heated/cooled) living space

Square footage must be between 400 and 10,000

Ceiling Height *

Climate Zone * i

Insulation Quality * i

Poor Pre-1980s, minimal insulation

Average 1980s–2000s, basic insulation

Good 2000s+, code-compliant

Excellent Modern, high-efficiency build

Advanced Factors

Fine-tune your estimate

Sun Exposure

Heavily Shaded Dense tree cover, north-facing

Partially Shaded Some trees or shade

Full Sun Direct sun most of the day

Number of Windows

Number of Occupants i

Each person adds ~600 BTU of heat

Kitchen Type

Small / No Kitchen Kitchenette or minimal

Standard Kitchen Typical stove, oven, fridge

Large Kitchen Multiple appliances, double oven

Home Type

Your Recommended System Size

3.0 TON

36,000 BTU

Smaller Larger

1.5T 2.0T 2.5T 3.0T 3.5T 4.0T 4.5T 5.0T

We recommend a system between 2.5 and 3.5 tons for your home. A professional load calculation will confirm the ideal size.

Too Small

Won't heat or cool adequately. Runs constantly, drives up energy bills, and shortens equipment life.

Too Large

Short-cycles on and off. Creates humidity problems, uneven temperatures, and wastes energy.

Common System Sizes for Reference

Small (800–1,200 sq ft)

1.5–2T

Medium (1,200–1,800 sq ft)

2–3T

Large (1,800–2,500 sq ft)

3–4T

Very Large (2,500+ sq ft)

4–5+T

Get an Exact Quote for Your Home

This calculator provides estimates. A professional load calculation ensures perfect sizing.

Call (781) 408-2506 Get Instant Quote

This calculator provides estimates based on standard HVAC industry formulas. A professional Manual J load calculation is recommended for final equipment sizing. Results may vary based on ductwork condition, air leakage, and other factors.

This calculator uses a simplified version of the Manual J load calculation methodology — the industry standard established by the Air Conditioning Contractors of America (ACCA). Professional HVAC technicians use the full Manual J process with detailed measurements.

Our formula starts with a base BTU-per-square-foot multiplier for your climate zone, then adjusts for:

Ceiling height — taller ceilings mean more air volume to condition
Insulation quality — better insulation retains conditioned air longer
Sun exposure — direct sunlight adds significant heat load
Windows — more glass means more heat gain/loss
Occupants — each person adds ~600 BTU of body heat
Kitchen load — cooking appliances generate substantial heat
Home layout — multi-story homes need more capacity for distribution

The result is converted to tons (1 ton = 12,000 BTU) and rounded to the nearest half-ton to match available equipment sizes.

"Going big just to be safe" — An oversized system short-cycles (turns on and off too frequently), leading to humidity problems, uneven temperatures, and premature wear. Bigger is not better.
Matching the old system size — If your previous system was installed 15+ years ago, it may have been improperly sized. New windows, added insulation, or sealed ducts can change your load significantly.
Ignoring home improvements — New windows, spray foam insulation, or a sealed attic can reduce your heating/cooling load by 20-30%. Always recalculate after upgrades.
Using "rule of thumb" alone — Simple square-footage rules ignore insulation, layout, sun exposure, and dozens of other factors that affect real-world performance.

This calculator gives solid estimates for most homes. However, a full Manual J load calculation by a licensed technician is recommended when:

Your home is over 3,500 sq ft — larger homes often need zoned systems
Complex or unusual layouts — additions, vaulted ceilings, sunrooms
Radiant heat or unusual systems — hydronic, geothermal, or hybrid setups
You're switching fuel types — oil to gas, gas to heat pump, etc.
Significant ductwork issues — old, leaky, or undersized ducts

Schedule a Professional Assessment

Our licensed technicians perform detailed load calculations as part of every installation quote. No pressure, no obligation.

Get a Free Quote