Introduction
When the winter design temperature is below 60ºF, the International Residential Code requires a dwelling to have heating facilities capable of maintaining a minimum room temperature of 68ºF in habitable rooms. Portable space heaters cannot be used to meet this requirement. A permanent heating system must be installed.
In buildings we refer to heat flow in a number of different ways. The most common reference is the R-value, or the resistance to heat flow. The higher the R-value of a material, the more it will restrict heat loss or gain. U-factor (sometimes referred to as U-value) is a measure of the flow of heat (thermal transmittance) through a material, given a difference in temperature on either side. In the inch-pound (I-P) system, the U-factor is the number of Btus (British Thermal Units) of energy passing through a square foot of the material in an hour for every degree Fahrenheit difference in temperature across the material (Btu/ft2hr°F or BtuH). In metric, the U-factor is usually given in watts per square meter per degree Celsius (w/m2°C).
Calculations of heat loss are made to determine whether a proposed heating (or cooling system) is adequate to supply and maintain the desired temperature within a structure as specified by code. These calculations are also used to estimate the annual heating or cooling costs of a system.
When the winter design temperature is below 60ºF, the International Residential Code requires a dwelling to have heating facilities capable of maintaining a minimum room temperature of 68ºF in habitable rooms. Portable space heaters cannot be used to meet this requirement. A permanent heating system must be installed.
In buildings we refer to heat flow in a number of different ways. The most common reference is the R-value, or the resistance to heat flow. The higher the R-value of a material, the more it will restrict heat loss or gain. U-factor (sometimes referred to as U-value) is a measure of the flow of heat (thermal transmittance) through a material, given a difference in temperature on either side. In the inch-pound (I-P) system, the U-factor is the number of Btus (British Thermal Units) of energy passing through a square foot of the material in an hour for every degree Fahrenheit difference in temperature across the material (Btu/ft2hr°F or BtuH). In metric, the U-factor is usually given in watts per square meter per degree Celsius (w/m2°C).
Calculations of heat loss are made to determine whether a proposed heating (or cooling system) is adequate to supply and maintain the desired temperature within a structure as specified by code. These calculations are also used to estimate the annual heating or cooling costs of a system.
- Use the 99 percent values from Appendix D of the International Plumbing Code or from the NOAA Engineering Design Data publication (http://160.36.48.42/escurriculum/weather_data/weather_data_summ.html). Alternatively, you may use a design temperature that reflects local climate or local weather experience as determined by the building official.
- The International Residential Code requirements/rule of thumb for a new house with good insulation is 1.25 watts per cu. ft. or 4.25 Btu per cu. ft.
- Important conversion information:
- watts x 3.21 = Btu/hr
- Btu/hr x .2931 = watts
Conclusion
1. Where does the greatest heat loss occur in this structure?
2. What was the most significant change made to make this structure more energy efficient?
3. What effect could using 2x6 studs in the shed construction have on energy heat loss/gain?
1. Where does the greatest heat loss occur in this structure?
2. What was the most significant change made to make this structure more energy efficient?
3. What effect could using 2x6 studs in the shed construction have on energy heat loss/gain?