# Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]

The dwelling has a floor area of 1500 square feet exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has a 12-kW range, a 2.5-kW water heater, a 1.2-kW dishwasher, 9 kW of electric space heating installed in five rooms, a 5-kW clothes dryer, and a 6-ampere, 230-volt room air-conditioning unit. Assume range, water heater, dishwasher, space heating, and clothes dryer kW ratings equivalent to kVA.

Air conditioner kVA calculation is 6A x 230V ÷ 1000 = 1.38 kVA

This 1.38 kVA [Item 1 from 220.82(C)] is less than 40% of 9 kVA of separately controlled electric heat [Item 6 from 220.82(C)], so the 1.38 kVA need not be included in the service calculation.

1500 sq. ft. at 3 volt-amperes

4500 VA

Two 20-amp. appliance outlet circuits at 1500 volt-amperes each

3000 VA

Laundry circuit

1500 VA

Range (at nameplate rating)

12,000 VA

Water heater

2500 VA

Dishwasher

1200 VA

Clothes dryer

5000 VA

Total

29,700 VA

Application of Demand Factor [See 220.82(B)]

 First 10 kVA of general load at 100% = 10,000 VA Remainder of general load at 40% (19.7 kVA x .4) = 7880 VA Total of general load = 17,880 VA 9 kVA of heat at 40% (9000 VA x .4) = 3600 VA Total = 21,480 VA

Therefore, the minimum service size would be 100 amperes in accordance with 230.42 and 230.79.

1500 sq. ft. at 3 volt-amperes

4500 VA

Three 20-amp. circuits at 1500 volt-amperes

4500 VA

Total

9000 VA

3000 volt-amperes at 100%

3000 VA

9000 VA - 3000 VA = 6000 volt-amperes at 35%

2100 VA

Subtotal

5100 VA

Range8 kVA at 70%

5600 VA

Clothes dryer5 kVA at 70%

3500 VA

Dishwasher

1200 VA

Total

15,400 VA