The Heating and Cooling Load calculator computes the amount of heat energy that conducts through a surface based on the temperature variance, surface area and coefficient of heat transmission.
INSTRUCTION: Choose units and enter the following:
- (A) Total Surface Area
- (ΔT) Interior to Exterior Temperature Variance
- (U) Coefficient of Heat Transfer in (W/m2⋅°C)
Heat or Cooling Load (HL): The heat transfer load is returned in watts and BTUs per hour. However, these can be automatically converted to compatible units via the pull-down menu.
The Math / Science
The formula for heating or cooling load is:
HL = A ⋅ U ⋅ Δt
where
- HL = Heating or Cooling Load (BTUs per hour or Watts)
- A = Exposed Surface Area
- U = Coefficient of overall heat transmission in W/(m2⋅°C) (see table below)
- Δt = Temperature Delta on either side of the surface
Coefficient of Heat Transmission (U)
The U-value, also known as the heat transfer coefficient, measures the rate at which heat transfers through a material or assembly of materials (like walls, windows, roofs, etc.). It is a critical factor in determining the thermal performance of building elements.
The U-value is expressed in units of watts per square meter per degree Celsius (W/m²°C) or in Imperial units, BTU per hour per square foot per degree Fahrenheit (BTU/h·ft²·°F). Essentially, it indicates how much heat energy passes through a specific material or assembly per unit area and per degree of temperature difference between the interior and exterior environments.
A lower U-value indicates better insulation properties because it means the material or assembly has lower heat conductivity and reduces heat transfer more effectively. Conversely, a higher U-value signifies higher heat transfer and poorer insulation properties.
U-values are used in building design and construction to ensure energy efficiency, as they help determine the insulation needs for various components like walls, windows, roofs, and doors. Lower U-values are desirable in colder climates to minimize heat loss from the interior, while in warmer climates, they can help reduce heat gain from the exterior.
| Construction Material Heat Transfer Coefficients (U) in W/(m2⋅°C) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Roof Material | Floors | Windows | Walls | ||||||
| Aerated Concrete | 0.16 | Concrete | 1.35 | Metal Frame (single glaze) | 5.7 | Solid Brick | 2.1 | ||
| Clay Tiles | 1 | Pine | 0.13 | Metal Frame (double glaze) | 3.4 | Brick + Insulation | 0.28 | ||
| Felt / Bitumen | 0.3 | Steel | 5.0 | Wood Frame (single glaze) | 4.8 | Solid Stone | 2.25 | ||
| Concrete Tile | 1.5 | Hardwood | 0.18 | Wood Frame (double glaze) | 2.8 | Stone + Insulation | 0.32 | ||
| Shingles (asphalt) | 0.5 | Wood Frame (triple glaze) | 2.1 | Concrete | 3 | ||||
| Wood Shingles | 0.1 | Vinyl Frame (single glaze) | 4.8 | Concrete + Insulation | 0.31 | ||||
| Vinyl Frame (double glaze) | 2.7 | Hollow Wall (air gap) | 1.3 | ||||||
| Vinyl Frame (triple glaze) | 1.9 | Hardwoods | 0.18 | ||||||
| Doors | Pine | 0.14 | |||||||
| Solid Wood | 3.0 | Drywall | 0.16 | ||||||
HVAC (Heating and Cooling) Calculators
- Air Change Rate: Computes the number of times per hour the air in a space changes based on the flow rate of fresh air and the volume of the space.
- Air Conditioner Size: Computes the number of BTUs needed to air condition a room with a window unit air conditioner based on the size of the room, number of occupants, sun exposure and use (kitchen or not).
- Arithmetic Mean Temperature Difference: Computes the mean temperature difference based on the temperatures of the primary and secondary inlets and outlets of a system.
- BTUs per hour to Heat a Room: Computes the energy (heat) required to heat a space of a certain volume by a specified temperature variance.
- Cross-section Area: Computes the cross-section area of a pipe or conduit based on the diameter.
- Heating and Cooling Load: Computes the amount of heat energy that conducts through a surface based on the temperature variance, surface area and coefficient of heat transmission.
- Heat Exchange Area: Computes the exchange material surface area required to achieve an overall heat transfer flow rate through a heat exchanger based on the heat transfer material coefficient, and the desired temperature difference at the two ends of the heat exchanger.
- Heating Load and Water Flow: Computes the ton of heat capacity associated with a volumetric flow of water and a change in temperature.
- Heat Loss through a Wall: Computes the amount of heat energy that conducts through a wall based on the temperature variance, surface area and coefficient of heat transmission.
- Heat Loss of a Room: Estimates the heat loss in a room based on the surface area of the interior of a rectangular room including the walls and ceiling, the temperature variance (inside and outside) and a coefficient of heat transfer.
- Temperature Transfer Efficiency: Computes the temperature transfer efficiency of a heat recovery unit.
- (U) Heat Transfer Coefficients: Description of the coefficient of heat transfer and the values associated with numerous materials.
- Insulation Calculator: Twenty (20) equations and data items related to insulation (rolls, cellulose. loose fiberglass and shake and rake)
- Ventilation Rate per Person: Computes the ventilation rate per person based on the flow rate of fresh air, volume of the space, occupant density and the ceiling height.
- Volume of a Room: Computes the volume of a room based on the height of the ceiling and the length and width of the floor.