Estimate the required cooling capacity (Tons and BTUs) for your living space based on square footage and environmental factors.
Excellent (New Construction, High R-Value)
Average (Standard Modern Home)
Poor (Old Home, Drafty, No Attic Insulation)
Estimated Requirements:
Your home requires approximately:
0 BTU/hr
0 Tons
*Note: HVAC sizing also depends on climate zone. Consult a professional for a full Manual J load calculation.
How HVAC Sizing Works
Choosing the right size for your Air Conditioning or Heat Pump system is critical for both comfort and energy efficiency. An undersized unit will run constantly, failing to cool the home on hot days. Conversely, an oversized unit will "short-cycle," turning on and off too quickly, which leads to high humidity and premature equipment failure.
The Calculation Formula
This calculator uses a simplified version of the Manual J method. The base logic follows these parameters:
Base Square Footage: Multiplied by an insulation factor (20 for tight homes, 35 for older homes).
Ceiling Height: Adjusts the volume. We increase the load by 10% for every foot above a standard 8ft ceiling.
Occupants: Each person generates heat. We add 500 BTUs per regular occupant.
Windows: Exterior glass accounts for significant heat gain. We add 1,000 BTUs per window/exterior door.
Example Calculation:
A 1,500 sq. ft. home with average insulation, 3 people, and 8 windows:
1. 1,500 x 25 = 37,500 BTUs (Base)
2. 3 People x 500 = 1,500 BTUs
3. 8 Windows x 1,000 = 8,000 BTUs Total: 47,000 BTUs (Approx. 4 Tons)
BTUs vs. Tons
In the HVAC industry, cooling capacity is measured in BTUs (British Thermal Units) or Tons. One "Ton" of cooling equals 12,000 BTUs per hour. This term originates from the amount of heat required to melt one ton of ice in a 24-hour period.
function calculateHVAC() {
var sqft = parseFloat(document.getElementById('sqft').value);
var insulation = parseFloat(document.getElementById('insulation').value);
var ceiling = parseFloat(document.getElementById('ceiling').value);
var occupants = parseFloat(document.getElementById('occupants').value);
var windows = parseFloat(document.getElementById('windows').value);
var resultDiv = document.getElementById('hvac-result');
var btuOutput = document.getElementById('btu-output');
var tonOutput = document.getElementById('ton-output');
if (isNaN(sqft) || sqft 8) {
var ceilingDiff = ceiling – 8;
var ceilingMultiplier = 1 + (ceilingDiff * 0.12); // 12% increase per foot
baseBTU = baseBTU * ceilingMultiplier;
}
// 3. Add Heat Load for Occupants (500 BTU per person)
var occupantLoad = occupants * 500;
// 4. Add Heat Load for Windows (1000 BTU per window)
var windowLoad = windows * 1000;
// 5. Calculate Total BTU
var totalBTU = baseBTU + occupantLoad + windowLoad;
// 6. Calculate Tonnage (12,000 BTU = 1 Ton)
var totalTons = totalBTU / 12000;
// Standard HVAC units come in half-ton increments.
// We round to the nearest 0.5 for realistic suggestion
var roundedTons = Math.ceil(totalTons * 2) / 2;
// Display results
btuOutput.innerHTML = Math.round(totalBTU).toLocaleString() + " BTU/hr";
tonOutput.innerHTML = roundedTons.toFixed(1) + " Tons";
resultDiv.style.display = "block";
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}