Load Calculations & Electric Heating
Dwelling unit load calculations, basic load allowance, demand factors, electric range loads, heating loads, small appliance allowances, and service sizing.
- Calculate the basic load allowance for a dwelling unit based on floor area
- Apply demand factors for lighting, range, and heating loads
- Perform dwelling unit service size calculations
- Apply Ohm's Law and power formulas to electrical problems
- Explain series and parallel circuit fundamentals
Leçon 1
Basic Load Allowance & Floor Area Calculations
Dwelling Unit Load Calculation
The dwelling unit load calculation determines the minimum service size needed for a home. The OESC 29th Edition (2024), effective May 1, 2025, provides a standardized method using the basic load allowance plus individual appliance loads. This calculation ensures the service entrance and conductors are large enough to handle peak demand. The 29th Edition added a new requirement to include Electric Vehicle Supply Equipment (EVSE) loads in demand calculations and mandates labeling of the maximum residential load on the service equipment to prevent future overloading.
Floor Area Calculation
The basic load is calculated from the total floor area of the dwelling:
- First 90 m2: 5000 watts
- Each additional 90 m2 (or portion): 1000 watts
The floor area includes all living space - bedrooms, living room, kitchen, dining room, hallways, and closets. It does not include unfinished basement, garage, or open porch areas.
Exam Tip
For a 1500 sq ft home (approximately 140 m2): first 90 m2 = 5000 W, remaining 50 m2 rounds up to one additional 90 m2 = 1000 W. Basic load = 6000 W. Always round up partial 90 m2 blocks.
Small Appliance and Laundry Loads
In addition to the basic load, add:
- 1500 watts for each required small appliance circuit (minimum 2 circuits = 3000 W)
- 1500 watts for the laundry circuit
These are fixed allowances regardless of actual appliance ratings.
The basic load allowance is 5000 W for the first 90 m2 plus 1000 W for each additional 90 m2. Add 1500 W per small appliance circuit (minimum 3000 W) and 1500 W for laundry. Always round up partial floor area blocks.