Adding new loads to an existing home's service

What the code requires

Section 220.83 gives an optional way to check whether an existing house can handle added load. It applies to dwelling services and feeders at 120/240 V or 208Y/120 V, 3-wire. Which part you use depends on whether air conditioning or electric space heat is being added.

If no A/C or electric space heat is being added, part (A) applies. Existing and new loads are counted: general lighting and receptacles at 3 VA per sq ft, 1,500 VA for each 20-A small-appliance circuit and each laundry circuit, and the nameplate rating of appliances that are fastened in place, permanently connected or on a specific circuit, plus ranges, wall ovens, counter-mounted cooktops, dryers not on the laundry circuit, and water heaters. The first 8 kVA counts at 100% and the remainder at 40%.

If A/C or electric space heat is being added, part (B) applies. The A/C counts at 100%, central electric space heat at 100%, and fewer than four separately controlled space-heating units at 100%. Only the larger of the cooling or heating load is counted, not both. All other loads then take the first 8 kVA at 100% and the remainder at 40%.

On the job

• Adding a heat pump or A/C means using part (B), with the air-conditioning load counted at 100%. Applying part (A)'s 40% factor to new HVAC is wrong under the 2023 code.
• Floor area is measured under 220.5(C). In the 2023 code the dwelling exclusions name only open porches and unfinished areas not adaptable for future use; garages are no longer on that list.
• The 2026 NEC revision cycle rewrites this calculation with different factors. California has not adopted that edition, so the 2023 numbers on this page are the ones that apply.
• In the standard calculation method, a related 2023 rule, 220.57, counts EV charging equipment at 7,200 W or its nameplate rating, whichever is larger. This page covers the optional method, so ask your inspector how EV equipment should be counted here.

In California

California does not amend this section. The 2025 CEC's electric-readiness amendments, which call for breaker spaces, circuits and panel busbar ratings under Energy Code 150.0, are separate requirements, not changes to this calculation.

Related sections

• NEC 220.5(C)
• NEC 220.57
• NEC 220.82: Optional load calculation for a single home
• NEC 220.87: Using actual demand data to size added load
• NEC 230.42: Sizing service-entrance conductors
• NEC 230.79: Minimum service size, including 100 A for homes

Where this comes from

• NFPA: CMP-2 First Draft working output, 2026 cycle (2023 base text of 220.83)
• Larimer County: 2023 NEC significant code changes
• ExpertCE: How the 2023 NEC changes dwelling unit load calculations
• Read the official NEC free at NFPA