Wells Mortgage Calculator

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HVAC Sizing & BTU Calculator

Excellent (New construction, high-efficiency windows) Average (Standard insulation, double-pane windows) Poor (Old home, drafts, single-pane windows)

Estimation Results:

Total Cooling Required: 0 BTU/hr

Recommended Unit Size: 0 Tons

Note: This is a simplified estimate based on standard HVAC formulas. For exact sizing, a professional Manual J calculation is recommended.

function calculateHVAC() { var sqft = parseFloat(document.getElementById('sqft').value); var insulation = parseFloat(document.getElementById('insulation').value); var occupants = parseFloat(document.getElementById('occupants').value); var windows = parseFloat(document.getElementById('windows').value); var doors = parseFloat(document.getElementById('extDoors').value); if (isNaN(sqft) || sqft <= 0) { alert("Please enter a valid square footage."); return; } // Calculation Logic // Base BTU = Area * Insulation Multiplier var baseBTU = sqft * insulation; // Add 200 BTU per occupant var occupantBTU = occupants * 200; // Add 100 BTU per window var windowBTU = windows * 100; // Add 100 BTU per exterior door var doorBTU = doors * 100; var totalBTU = baseBTU + occupantBTU + windowBTU + doorBTU; // 1 Ton = 12,000 BTU var totalTons = totalBTU / 12000; // Round to nearest 0.5 ton for standard unit sizing var roundedTons = Math.ceil(totalTons * 2) / 2; document.getElementById('btuOutput').innerHTML = Math.round(totalBTU).toLocaleString(); document.getElementById('tonOutput').innerHTML = roundedTons.toFixed(1); document.getElementById('hvacResult').style.display = 'block'; }

How to Calculate the Right HVAC Size for Your Home

Choosing the correct HVAC unit size is critical for both home comfort and energy efficiency. An undersized unit will run constantly without cooling your home, while an oversized unit will "short cycle," turning on and off too quickly, which leads to humidity problems and premature wear on the compressor.

Key Factors in BTU Calculation

While square footage is the primary factor, professional HVAC contractors use several variables to determine the "Manual J Load Calculation." Our calculator uses the following metrics:

  • Square Footage: The total conditioned area that needs cooling and heating.
  • Insulation Multiplier: Better insulation traps conditioned air more effectively. High-efficiency homes require fewer BTUs per square foot (approx. 20) compared to older homes with poor insulation (up to 30+).
  • Occupants: Humans generate heat. We factor in 200 BTUs per person for average activity levels.
  • Windows and Doors: These are the primary points of thermal transfer. Each window and exterior door adds to the cooling load.

Realistic Sizing Example

Imagine a 2,000-square-foot home with average insulation, 4 occupants, 10 windows, and 3 exterior doors:

  1. Base BTU: 2,000 sq. ft. x 25 = 50,000 BTUs
  2. Occupants: 4 x 200 = 800 BTUs
  3. Windows: 10 x 100 = 1,000 BTUs
  4. Doors: 3 x 100 = 300 BTUs
  5. Total: 52,100 BTUs

Since 1 Ton of cooling equals 12,000 BTUs, this home would require approximately 4.34 tons. In practice, a 4.5-ton unit would be the appropriate professional choice.

What is a "Ton" of Cooling?

In the HVAC industry, a "ton" does not refer to the weight of the equipment. It is a measurement of heat removal capacity. One ton of cooling capacity is equivalent to the amount of heat required to melt 2,000 pounds (one ton) of ice over a 24-hour period. This equals exactly 12,000 BTUs per hour.

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