This calculator provides an estimate. Actual savings may vary based on climate, home construction, air leakage, and energy price fluctuations.
function calculateInsulationSavings() {
// Get input values
var wallArea = parseFloat(document.getElementById("wallArea").value);
var currentRValue = parseFloat(document.getElementById("currentRValue").value);
var addedRValue = parseFloat(document.getElementById("addedRValue").value);
var heatingCostPerTherm = parseFloat(document.getElementById("heatingCostPerTherm").value);
var annualHeatingDegreeDays = parseFloat(document.getElementById("annualHeatingDegreeDays").value);
var furnaceEfficiency = parseFloat(document.getElementById("furnaceEfficiency").value);
var coolingCostPerKWH = parseFloat(document.getElementById("coolingCostPerKWH").value);
var annualCoolingDegreeDays = parseFloat(document.getElementById("annualCoolingDegreeDays").value);
var acSEER = parseFloat(document.getElementById("acSEER").value);
var resultDiv = document.getElementById("result");
resultDiv.style.display = "none"; // Hide previous results
resultDiv.innerHTML = ""; // Clear previous results
// Validate inputs
if (isNaN(wallArea) || wallArea <= 0 ||
isNaN(currentRValue) || currentRValue <= 0 ||
isNaN(addedRValue) || addedRValue <= 0 ||
isNaN(heatingCostPerTherm) || heatingCostPerTherm <= 0 ||
isNaN(annualHeatingDegreeDays) || annualHeatingDegreeDays < 0 ||
isNaN(furnaceEfficiency) || furnaceEfficiency 100 ||
isNaN(coolingCostPerKWH) || coolingCostPerKWH <= 0 ||
isNaN(annualCoolingDegreeDays) || annualCoolingDegreeDays < 0 ||
isNaN(acSEER) || acSEER <= 0) {
resultDiv.style.display = "block";
resultDiv.style.backgroundColor = "#f8d7da"; // Error color
resultDiv.style.color = "#721c24";
resultDiv.innerHTML = "Please enter valid positive numbers for all fields. Furnace efficiency must be between 1 and 100.";
return;
}
// Convert furnace efficiency to a decimal
var furnaceEfficiencyDecimal = furnaceEfficiency / 100;
// Calculate U-values
var initialTotalRValue = currentRValue;
var finalTotalRValue = currentRValue + addedRValue;
var initialUValue = 1 / initialTotalRValue;
var finalUValue = 1 / finalTotalRValue;
var deltaUValue = initialUValue – finalUValue; // Reduction in U-value
// — Heating Savings Calculation —
// Heat loss reduction in BTU per year
// Formula: Area * Delta_U * 24 hours/day * Heating Degree Days
var heatingBTUSaved = wallArea * deltaUValue * 24 * annualHeatingDegreeDays;
// Convert BTU saved to Therms (1 Therm = 100,000 BTU)
var heatingThermsSaved = heatingBTUSaved / 100000;
// Calculate actual fuel cost savings, accounting for furnace efficiency
var annualHeatingCostSavings = (heatingThermsSaved / furnaceEfficiencyDecimal) * heatingCostPerTherm;
// — Cooling Savings Calculation —
// Heat gain reduction in BTU per year
// Formula: Area * Delta_U * 24 hours/day * Cooling Degree Days
var coolingBTUSaved = wallArea * deltaUValue * 24 * annualCoolingDegreeDays;
// Convert BTU saved to kWh (SEER is BTU/Wh, 1 kWh = 1000 Wh)
// Electrical energy saved (kWh) = BTU_saved / (SEER * 1000)
var coolingKWHReduced = coolingBTUSaved / (acSEER * 1000);
// Calculate cooling cost savings
var annualCoolingCostSavings = coolingKWHReduced * coolingCostPerKWH;
// — Total Annual Savings —
var totalAnnualSavings = annualHeatingCostSavings + annualCoolingCostSavings;
// Display results
resultDiv.style.display = "block";
resultDiv.style.backgroundColor = "#d4edda"; // Success color
resultDiv.style.color = "#155724";
resultDiv.innerHTML =
"Estimated Annual Savings:" +
"Heating Cost Savings: $" + annualHeatingCostSavings.toFixed(2) + "" +
"Cooling Cost Savings: $" + annualCoolingCostSavings.toFixed(2) + "" +
"Total Annual Energy Cost Savings: $" + totalAnnualSavings.toFixed(2) + "";
}
Understanding Wall Insulation and Its Benefits
Insulating your walls is one of the most effective ways to improve your home's energy efficiency, reduce utility bills, and enhance indoor comfort. Heat naturally flows from warmer areas to colder areas. In winter, heat escapes through your walls to the colder outdoors, and in summer, outdoor heat penetrates your walls into your cooler home. Proper insulation acts as a barrier, slowing this heat transfer.
What is R-value?
R-value is a measure of thermal resistance. It indicates how well a material resists the conductive flow of heat. A higher R-value means greater insulating power. For walls, the total R-value includes the insulation material itself, as well as the R-values of other components like drywall, sheathing, and siding. When you add insulation, you are increasing the overall R-value of your wall assembly.
How Does Wall Insulation Work?
Insulation materials, such as fiberglass batts, cellulose, spray foam, or rigid foam boards, contain millions of tiny air pockets. These air pockets trap air, preventing it from circulating and transferring heat. This significantly reduces heat loss in winter and heat gain in summer, leading to a more stable indoor temperature and less reliance on your heating and cooling systems.
Key Benefits of Insulating Your Walls:
Lower Energy Bills: This is often the primary motivation. By reducing heat transfer, your HVAC system doesn't have to work as hard, directly translating to lower heating and cooling costs.
Improved Comfort: Well-insulated walls mean fewer cold spots in winter and cooler surfaces in summer, leading to a more consistent and comfortable indoor environment.
Reduced Noise: Many insulation materials also have sound-dampening properties, helping to reduce noise transmission from outside or between rooms.
Environmental Impact: Lower energy consumption means a reduced carbon footprint, contributing to a healthier planet.
Increased Home Value: Energy-efficient homes are often more attractive to potential buyers.
Understanding Degree Days (HDD & CDD)
Heating Degree Days (HDD) and Cooling Degree Days (CDD) are simplified measurements used to quantify the demand for heating and cooling over a period. They are based on the difference between the average daily outdoor temperature and a standard "base temperature" (usually 65°F or 18°C).
Heating Degree Days (HDD): When the average daily temperature is below the base temperature, heating is typically required. The number of HDD for a day is the difference between the base temperature and the average daily temperature. A higher annual HDD value indicates a colder climate and a greater need for heating.
Cooling Degree Days (CDD): Conversely, when the average daily temperature is above the base temperature, cooling is typically required. The number of CDD for a day is the difference between the average daily temperature and the base temperature. A higher annual CDD value indicates a warmer climate and a greater need for cooling.
These metrics help estimate the energy load on a building due to outdoor temperature fluctuations, making them crucial for calculating potential energy savings from insulation.
How Our Calculator Works
Our Wall Insulation Savings Calculator estimates your potential annual energy cost savings by comparing the heat transfer through your walls before and after adding insulation. It takes into account:
Wall Area: The total surface area of the walls you plan to insulate.
Current Wall R-value: The existing thermal resistance of your wall structure.
Added Insulation R-value: The R-value of the new insulation material you intend to install.
Heating & Cooling Costs: Your local energy prices for heating fuel (e.g., natural gas, propane, oil) and electricity for cooling.
Annual Heating & Cooling Degree Days: Climate data specific to your region, indicating the typical heating and cooling demands.
HVAC System Efficiency: The efficiency of your furnace (AFUE) and air conditioner (SEER) directly impacts how much fuel/electricity is consumed to meet the heating/cooling load.
By inputting these details, the calculator estimates the reduction in heat loss and gain, converts that into energy savings, and then calculates the monetary savings based on your energy costs and system efficiencies.
Getting Started with Wall Insulation
Before you begin, it's important to assess your current wall insulation. This might involve a home energy audit or inspecting accessible areas like attics or basements. Common methods for insulating existing walls include:
Blown-in Insulation: Cellulose or fiberglass can be blown into wall cavities through small holes drilled from the exterior or interior.
Batt Insulation: If walls are open (e.g., during a renovation), fiberglass or mineral wool batts can be easily installed between studs.
Rigid Foam Boards: Can be added to the exterior of walls during re-siding projects, providing continuous insulation and reducing thermal bridging.
Consult with a qualified insulation contractor to determine the best approach and R-value recommendations for your specific home and climate zone.