Each apartment in a 30-unit apartment complex has a 2 kW water heater. Using the optional method, what is the demand on the service for these water heaters?

Each apartment in a 30-unit apartment complex has a 2 kW water heater. Using the optional method, what is the demand on the service for these water heaters?

• A. 14.85 kW
• B. 18.2 kW
• C. 19.8 kW
• D. 60 kW

Answer: (C)

The optional method reduces the calculated service load by applying a fixed demand factor to the total rating of electric water heaters, rather than adding every unit at full nameplate power. For a dwelling with 30 or more units, the code uses a demand factor of about one-third for water heaters. Total heater rating: 30 units × 2 kW each = 60 kW. Applying the 33% factor: 60 kW × 0.33 ≈ 19.8 kW. So, the demand on the service is 19.8 kW. (Using full load would be 60 kW, which isn’t the method here.)

The optional method reduces the calculated service load by applying a fixed demand factor to the total rating of electric water heaters, rather than adding every unit at full nameplate power. For a dwelling with 30 or more units, the code uses a demand factor of about one-third for water heaters.

Total heater rating: 30 units × 2 kW each = 60 kW. Applying the 33% factor: 60 kW × 0.33 ≈ 19.8 kW.

So, the demand on the service is 19.8 kW. (Using full load would be 60 kW, which isn’t the method here.)