Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)

Example No D2(c) Optional Calculation for One Family Dwelling with Heat Pump(Single Phase, 240 120 Volt Service) (See 220 82)

Dwelling has a floor area of 2000 sq. ft. exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has a 12-kW range, 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW clothes dryer, a 2 ½-ton (24-ampere) heat pump with 15-kW of back-up heat.

Heat Pump kVA Calculation

This 5.76 kVA is less than 15 kVA of the backup heat; therefore, the heat pump load need not be included in the service calculation. [See 220.82(C).]

General Load


2000 sq. ft. at 3 volt-amperes

6000 VA

Two 20-ampere appliance outlet circuits at 1500 volt-amperes each

3000 VA

Laundry circuit

1500 VA

Range (at nameplate rating)

12,000 VA

Water heater

4500 VA


1200 VA

Clothes dryer

5000 VA

Subtotal general load

33,200 VA

First 10 kVA of general load at 100%

= 10,000 VA

Remainder of general load at 40% (23,200 VA x 0.4)

= 9280 VA

Total net general load

= 19,280 VA

Heat Pump and Supplementary Heat[*]

240V x 24A = 5,760 VA

15-kW electric heat:

5760 VA + (15,000 VA x 65%) = 5.76 kVA + 9.75 kVA = 15.51 kVA

[*] If supplementary heat is not on at the same time as heat pump, heat pump kVA need not be added to total.



Net general load

19,280 VA

Heat pump and supplementary heat

15,510 VA


34,790 VA

Calculated Load for Service

Therefore, this dwelling unit may be served by a 150-ampere service.

Article 90 Introduction


Wiring and Protection

Wiring Methods and Materials

Equipment for General Use

Special Occupancies

Special Equipment

Special Conditions


Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

Annex D. Examples

Annex E. Types of Construction

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Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120
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