Dwelling unit load calculation practice

Step 1: General lighting load

Multiply the living area by 3 volt-amperes per square foot. Use the outside dimensions of the dwelling and leave out open porches, garages and unfinished spaces that can't be adapted for future use. 220.12

Step 2: Small-appliance and laundry circuits

Add 1,500 VA for each 20-ampere small-appliance branch circuit. There are at least two in every dwelling. Add another 1,500 VA for the laundry circuit. 220.52

Step 3: Lighting demand factors

Take the total from steps 1 and 2 and apply the demand factors from Table 220.42. The first 3,000 VA counts at 100%. Everything from 3,001 to 120,000 VA counts at 35%. Anything over 120,000 VA counts at 25%.

Step 4: Fastened-in-place appliances

Add up appliances like the dishwasher, disposer, water heater and built-in microwave. If there are four or more, you can take 75% of the total. The range, dryer, space heating and air conditioning don't count toward the four. 220.53

Step 5: Clothes dryer

Use 5,000 VA or the nameplate rating, whichever is larger. A 4,500 W dryer still counts as 5,000 VA. 220.54

Step 6: Range

For one household range rated 12 kW or less, Column C of Table 220.55 gives a demand of 8 kW. For a larger range, increase the 8 kW by 5% for each kilowatt, or major fraction of a kilowatt, over 12. A 14 kW range is 2 kW over, so it's 8 kW × 1.10 = 8.8 kW.

Step 7: Heating or air conditioning

Electric heat and air conditioning don't run at the same time, so they're noncoincident loads. Include only the larger of the two. 220.60

Steps 8 and 9: Total and amperes

Add the demand results from steps 3 through 7. Divide the total by 240 volts to get the service load in amperes.

Worked example

A 2,000 sq ft dwelling has a dishwasher (1,200 VA), disposer (900 VA), water heater (4,500 VA), built-in microwave (1,500 VA), a 5,500 W dryer, a 14 kW range, 8,000 W of electric heat and a 4,800 VA air conditioner.

Common load calculation mistakes

• Skipping the lighting demand factor. Carrying the full lighting and small-appliance total forward adds thousands of VA.
• Applying 75% to three appliances. The fastened-in-place demand factor needs four or more.
• Counting the range or dryer as a fixed appliance. They have their own rules in 220.54 and 220.55.
• Adding heat and A/C together. Only the larger one goes in.
• Using the range nameplate. One range up to 12 kW is 8 kW, not its nameplate.
• Dividing by 208 or 120. A single-family service at 120/240 V is divided by 240.

Standard method vs optional method

Section 220.82 gives an optional method for dwellings that often produces a smaller service size. It uses different demand factors and a different heating and cooling rule. Exam questions will tell you which method to use. CalcReps currently drills the standard method, which most questions use.

Code edition note

These problems follow the 2023 NEC. The 2026 NEC moves the load calculation rules into a new Article 120, so the article numbers change if your state has adopted the 2026 edition. The math is the same for these steps, but always check which edition your exam uses.

How long should a load calculation take?

On the Texas Calculations exam you have about 4 minutes and 14 seconds per question on average. A full dwelling calculation takes most people longer than that at first. Drill it until you can finish in under six minutes, and bank time on shorter questions like voltage drop and box fill.