Calculate the Rate of Heat Conduction Through House Walls

House Wall Heat Conduction Calculator

Results

Heat Flow Rate (Q): 0 Watts

function calculateHeatLoss() { var k = parseFloat(document.getElementById('conductivity').value); var A = parseFloat(document.getElementById('wallArea').value); var T1 = parseFloat(document.getElementById('tempIn').value); var T2 = parseFloat(document.getElementById('tempOut').value); var d = parseFloat(document.getElementById('wallThickness').value); var resultBox = document.getElementById('resultBox'); var heatResult = document.getElementById('heatResult'); var energyInterpretation = document.getElementById('energyInterpretation'); if (isNaN(k) || isNaN(A) || isNaN(T1) || isNaN(T2) || isNaN(d) || d <= 0) { alert("Please enter valid positive numbers for all fields. Thickness must be greater than zero."); return; } // Formula: Q = k * A * (T_hot – T_cold) / d var tempDiff = Math.abs(T1 – T2); var Q = (k * A * tempDiff) / d; heatResult.innerHTML = Q.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); var totalDailyLoss = (Q * 24) / 1000; // kWh per day energyInterpretation.innerHTML = "This wall is losing approximately " + totalDailyLoss.toFixed(2) + " kWh of energy per day through conduction."; resultBox.style.display = 'block'; }

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Understanding Heat Conduction through House Walls

Heat conduction is the process by which thermal energy is transferred through a solid material from a region of high temperature to a region of lower temperature. In the context of a home, this represents the heat escaping through your walls during winter or entering your home during a hot summer day.

The Physics: Fourier's Law

The rate of heat transfer is governed by Fourier's Law of Heat Conduction. The formula used in this calculator is:

Q = (k × A × ΔT) / d

• Q: The rate of heat flow (measured in Watts).
• k: Thermal conductivity of the material (W/m·K). This measures how well a material conducts heat.
• A: The total surface area of the wall (m²).
• ΔT: The temperature difference between the inside and outside (°C or K).
• d: The thickness of the wall material (meters).

Common Material Conductivity Values (k)

To use the calculator accurately, you need the thermal conductivity (k-value) of your wall material. Typical values include:

Material	Conductivity (W/m·K)
Common Brick	0.60 – 1.00
Concrete	1.00 – 1.70
Softwood	0.12 – 0.15
Fiberglass Insulation	0.04
Expanded Polystyrene (EPS)	0.033

How to Reduce Heat Loss

Looking at the formula, there are three primary ways to reduce the energy lost through your walls:

1. Lower the Conductivity (k): Replace air gaps or solid materials with high-performance insulation. The lower the k-value, the better the insulator.
2. Increase Thickness (d): This is why adding thicker layers of insulation or building thicker walls helps maintain internal temperatures.
3. Manage Temperature Difference (ΔT): While you can't control the weather, using smart thermostats to avoid over-heating or over-cooling can reduce the delta, thereby slowing heat transfer.

Example Calculation

If you have a brick wall (k = 0.7) with an area of 25m², a thickness of 0.3m (30cm), an indoor temperature of 20°C, and an outdoor temperature of 0°C:

Q = (0.7 × 25 × 20) / 0.3 = 1,166.67 Watts

This means your heating system needs to provide roughly 1.17 kW of power just to offset the heat lost through that single wall to maintain the temperature.