Building performance demoHeat Load CalculatorEstimate whole-building heating and cooling loads from envelope, glazing, climate, infiltration, and internal gains using a live SpreadsheetWeb model.Configure the building ↓Live workbook modelBuild a whole-house load scenarioStart with the published example, then adjust the building and design conditions. Valid changes recalculate automatically.Unit system?IP uses feet, square feet, degrees Fahrenheit, and Btu/h. SI uses metres, square metres, degrees Celsius, and watts. Values are converted when you switch.IPSIClimate preset ?Choose Custom to use the design-condition fields below, or select an illustrative workbook preset.Custom (use the values below)Very cold, illustrativeCold, illustrativeMixed, illustrativeMarine, illustrativeHot-humid, illustrativeHot-dry, illustrativeReset exampleChanging unit systems converts the current values while retaining unrounded canonical values to prevent toggle drift.01Building profileDefine the size, infiltration, occupancy, and altitude.Conditioned floor area?The conditioned floor area served by the system. Enter square feet in IP or square metres in SI.Average ceiling height?The average floor-to-ceiling height used with floor area to estimate conditioned volume.Air changes per hour?Estimated complete air replacements per hour caused by infiltration. Lower values describe tighter buildings.Number of occupants?The typical number of people whose sensible and latent heat gains are included.Altitude above sea level?Site elevation above sea level. The workbook uses it when estimating air-pressure effects.02Design conditionsThese six values drive the workbook only when the Custom preset is selected.Indoor winter temperature?The desired indoor dry-bulb temperature used for the winter design condition.Indoor summer temperature?The desired indoor dry-bulb temperature used for the summer design condition.Indoor summer relative humidity?The target indoor summer moisture level, expressed as relative humidity.Outdoor winter design temperature?The outdoor dry-bulb temperature used to estimate the design heating load.Outdoor summer design temperature?The outdoor dry-bulb temperature used to estimate the design cooling load.Outdoor summer relative humidity?The outdoor summer moisture level used in the latent cooling calculation.03Internal gains and allowancesAccount for people, plug loads, ducts, sizing allowance, and supply-air difference.Appliance load?Sensible heat released indoors by appliances and plug loads, entered in watts.Lighting load?Sensible heat released indoors by lighting, entered in watts.Sensible gain per person?Heat from each person that raises air temperature, shown in Btu/h (IP) or watts (SI).Latent gain per person?Moisture-related heat from each person, shown in Btu/h (IP) or watts (SI).Duct loss allowance?Additional percentage allowed for heat gained or lost through the duct system.Safety factor?Additional percentage applied by the workbook as a sizing allowance.Supply air temperature difference?Temperature difference between room air and supply air used to estimate required airflow.04Opaque envelope assembliesChoose each construction, enter its area, and optionally override the workbook R-value.#Construction ?The envelope construction selected from the workbook library. Its thermal resistance is used unless you provide an override.Area ?The exposed surface area of this assembly, entered in square feet (IP) or square metres (SI).R override ?Leave blank to let the workbook derive thermal resistance from the selected construction. Enter a value only to override it.R used ?The thermal resistance the workbook actually uses after applying the construction default or your override.UA ?Overall heat-transfer coefficient multiplied by area. Lower UA means less conductive heat flow through that assembly.1Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——2Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——3Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——4Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——5Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——6Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——7Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——8Wall, wood frame 2x4 with R13 battWall, wood frame 2x6 with R21 battWall, frame with R13 batt plus R5 continuousWall, uninsulated frameCeiling under vented attic, R38Ceiling under vented attic, R49Roof deck, unvented with R30Floor over unconditioned space, R19Floor over unconditioned space, R30Basement wall, R10 continuousSlab edge, R5 verticalDoor, insulated steel——05Glazing by orientationEnter window and skylight area, U-factor, and solar heat gain coefficient (SHGC).OrientationArea ?The window or skylight area facing this orientation, in square feet (IP) or square metres (SI).U-factor ?Rate of heat transfer through glazing. Lower U-factor means better insulation.SHGC ?Solar heat gain coefficient: the fraction of incident solar heat transmitted through the glazing, from 0 to 1.Solar gain factor ?The workbook's orientation-specific solar load factor before glazing area and SHGC are applied.North—East—South—West—Horizontal (skylight)—Workbook resultsEstimated design loadsCalculated from the published SpreadsheetWeb model using the current configuration.Waiting for a valid modelHeating load ?The total design heating rate estimated by the workbook from envelope and infiltration losses plus allowances.—Cooling load ?The total sensible and latent design cooling rate estimated by the workbook.—Cooling capacity ?The cooling load expressed as nominal equipment capacity. This is an illustrative workbook result, not equipment-selection advice.—Required airflow ?The estimated supply airflow required at the entered supply-air temperature difference.—Heating breakdown ?Shows how conduction, infiltration, ducts, and other workbook terms contribute to the total heating load.Adjust a value to calculate the load.Cooling breakdown ?Shows how envelope, solar, infiltration, people, appliances, and lighting contribute to the total cooling load.Adjust a value to calculate the load.View calculation detailsHeating calculation ?Workbook line items behind the heating total, including temperature difference and heat-transfer terms.Waiting for results.Cooling calculation ?Workbook line items behind the sensible and latent cooling total.Waiting for results.Sizing metrics ?Derived capacity, sensible-heat ratio, airflow, and area-normalized metrics reported by the workbook.Waiting for results.A concise modelWhat the workbook combinesEnvelopeOpaque assemblies, glazing area, U-factor, and SHGC.ClimateWinter, summer, humidity, altitude, and infiltration.Internal loadsPeople, appliances, lighting, ducts, and sizing allowance.
Heating load ?The total design heating rate estimated by the workbook from envelope and infiltration losses plus allowances.—
Cooling capacity ?The cooling load expressed as nominal equipment capacity. This is an illustrative workbook result, not equipment-selection advice.—
Required airflow ?The estimated supply airflow required at the entered supply-air temperature difference.—
