Window Heat Gain Calculator

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Window Heat Gain Calculator

Unit System

Imperial (°F, BTU, ft)SI (°C, kW, m)

Window Dimensions

Window Width (ft)

Window Height (ft)

Glazing Properties

Center-of-Glass U-Value (BTU/hr·ft²·°F)

Solar Heat Gain Coefficient (SHGC)

Frame Properties

Frame Width (inches)

Frame U-Value (BTU/hr·ft²·°F)

Frame Material

Edge Effects

Edge Width (inches)

Edge Factor

Design Conditions

Outdoor Temperature (°F)

Indoor Temperature (°F)

Solar Radiation (BTU/hr·ft²)

Orientation

Shading Devices

Has Overhang

Overhang Projection (ft)

Overhang Height Above Window (ft)

Has Blinds

Blind Type

Blind Openness (%)

Blind Transmittance

Blind Position

Infiltration

Infiltration Rate (CFM/ft²)

Results

Window Heat Gain Summary

387

Total Heat Gain BTU/hr

Heat Gain per Area BTU/hr/sq ft

181

Conductive Gain BTU/hr

180

Solar Gain BTU/hr

Infiltration Gain BTU/hr

Whole-Window U-Value BTU/hr·ft²·°F

Effective SHGC

Total Shading Factor

Heat Gain Breakdown

Heat Gain Distribution

Detailed Breakdown

Conductive Heat Gain (46.7%)181 BTU/hr

Solar Heat Gain (46.6%)180 BTU/hr

Infiltration Heat Gain (6.7%)25.92 BTU/hr

Calculation Steps

Calculate Window Area Breakdown

Formula:

A_{total} = W \times H

Calculation:

A_{total} = 6 \times 4 = 24.00

Result:

24.00 \text{ sq ft}

Calculate Frame Area

Formula:

A_{frame} = P \times W_{frame}

Calculation:

A_{frame} = 20.00 \times 0.167 = 3.33

Result:

3.33 \text{ sq ft}

Calculate Edge-of-Glass Area

Formula:

A_{edge} = 2(W + H) \times W_{edge} - 4W_{edge}^2

Calculation:

A_{edge} = 2(6 + 4) \times 0.208 - 4(0.208)^2 = 3.99

Result:

3.99 \text{ sq ft}

Calculate Edge-of-Glass U-Value

Formula:

U_{edge} = U_{cg} \times F_{edge}

Calculation:

U_{edge} = 0.35 \times 1.1 = 0.385

Result:

0.385 \text{ BTU/hr·ft²·°F}

Calculate Whole-Window U-Value

Formula:

U_{whole} = \frac{U_{cg} \times A_{cg} + U_{edge} \times A_{edge} + U_{frame} \times A_{frame}}{A_{total}}

Calculation:

U_{whole} = \frac{0.35 \times 16.67 + 0.385 \times 3.99 + 0.5 \times 3.33}{24.00}

Result:

0.377 \text{ BTU/hr·ft²·°F}

Calculate Conductive Heat Gain

Formula:

Q_{cond} = U_{whole} \times A \times (T_{outdoor} - T_{indoor})

Calculation:

Q_{cond} = 0.377 \times 24.00 \times (95 - 75)

Result:

180.80 \text{ BTU/hr}

Calculate Overhang Shading Factor

Formula:

F_{shading,overhang} = \frac{H_{window} - L_{shadow}}{H_{window}}

Calculation:

F_{shading,overhang} = \frac{4 - 1.69}{4}

Result:

0.579 \text{ }

Calculate Blind Shading Factor

Formula:

F_{shading,blind} = F_{open} + (1 - F_{open}) \times \tau_{blind}

Calculation:

F_{shading,blind} = 0.050 + (1 - 0.050) \times 0.1

Result:

0.145 \text{ }

Calculate Total Shading Factor and Effective SHGC

Formula:

F_{shading,total} = F_{shading,overhang} \times F_{shading,blind}

Calculation:

F_{shading,total} = 0.579 \times 0.145 = 0.084

Result:

0.084 \text{ }

Calculate Effective SHGC

Formula:

SHGC_{effective} = SHGC \times F_{shading,total}

Calculation:

SHGC_{effective} = 0.4 \times 0.084

Result:

0.034 \text{ }

Calculate Solar Heat Gain

Formula:

Q_{solar} = A \times I_{solar} \times SHGC_{effective} \times F_{orientation}

Calculation:

Q_{solar} = 24.00 \times 280 \times 0.034 \times 0.80

Result:

180.43 \text{ BTU/hr}

Calculate Infiltration Heat Gain

Formula:

Q_{infil} = 1.08 \times CFM_{infil} \times (T_{outdoor} - T_{indoor})

Calculation:

Q_{infil} = 1.08 \times 1.20 \times (95 - 75)

Result:

25.92 \text{ BTU/hr}

Calculate Total Window Heat Gain

Formula:

Q_{total} = Q_{cond} + Q_{solar} + Q_{infil}

Calculation:

Q_{total} = 180.80 + 180.43 + 25.92

Result:

387.14 \text{ BTU/hr}