Manual J calculator · NC
Manual J load calculation for North Carolina.
Reference data for Manual J load calculations in North Carolina: ASHRAE design temperatures for 4 top metros, energy code status, and NC PHFS licensing. The calculator does not load this page's data. It asks for your project location and looks up outdoor design conditions in its own dataset, by IECC 2021 climate zone for a ZIP code or by weather station for the 10 major metros in its city list.
Reference metro
Charlotte, NC (Mecklenburg County) · IECC 2015 zone 3A · winter 99% DB 22°F · summer 0.4% DB 94°F · MCWB 74°F.
Design DB: ASHRAE 169-2021 · ACCA MJ8 §6
Free · No signup · Daily limit applies
01 · ASHRAE design conditions
Top 4 metros in North Carolina - design temperatures used in Manual J.
These are the ASHRAE 99% heating and 0.4% cooling design temperatures, not the absolute extremes. Outdoor temperatures go past the 0.4% cooling value about 35 hours per year and below the 99% heating value about 88 hours per year.
| Metro | County | Zone (IECC 2015) | Winter 99% DB | Summer 0.4% DB | MCWB |
|---|---|---|---|---|---|
| Charlotte | Mecklenburg County | 3A | 22°F | 94°F | 74°F |
| Raleigh-Durham | Wake / Durham County | 4A | 20°F | 93°F | 75°F |
| Greensboro | Guilford County | 4A | 18°F | 92°F | 74°F |
| Asheville | Buncombe County | 4A | 10°F | 87°F | 71°F |
Design temperatures come from ASHRAE 169-2021, republished in EERE Building America Guide 7.3 (public domain). DB = dry-bulb. MCWB = mean coincident wet-bulb at the 0.4% cooling design hour.
Zones in this table are from the IECC 2015 county map (PNNL county data). For a ZIP code, BuildSolver's calculator assigns zones by the IECC 2021 county map, where Raleigh-Durham is 3A (not 4A); Greensboro is 3A (not 4A). A ZIP code near a zone line can get the neighboring zone.
02 · Energy code
Energy code baseline in North Carolina is North Carolina Energy Conservation Code 2018 (based on IECC 2015 with NC amendments).
In effect since 2019. Manual J load-calc documentation requirements flow from the state energy code; verify your specific AHJ's submittal rules before relying on the baseline.
- NC enforces the 2018 North Carolina Energy Conservation Code, its state amendments to IECC 2015, effective January 1, 2019.
Code status from NC Office of State Fire Marshal - Codes, current and past, verified October 6, 2026.
03 · North Carolina HVAC labor data
BLS wages and employment for HVAC mechanics in North Carolina.
These are state-level wages for occupation code 49-9021 - Heating, Air Conditioning, and Refrigeration Mechanics and Installers - from the most recent BLS Occupational Employment and Wage Statistics release.
- Median hourly wage
- $27.53
- Mean annual wage
- $57,400
- Employment estimate
- 15,230
Wage figures from BLS OEWS May 2025, SOC 49-9021 (state-level), released May 15, 2026.
04 · License & permit
HVAC licensing in North Carolina runs through NC PHFS.
State-level HVAC contractor licensing is administered by the North Carolina State Board of Examiners of Plumbing, Heating and Fire Sprinkler Contractors. Licenses renew annually.
License types
- H-1 Heating Group 1 (steam and hot-water systems)
- H-2 Heating Group 2 (systems over 15 tons of refrigeration capacity)
- H-3 Heating Group 3 (systems of 15 tons or less, and all single-family residences regardless of size)
- Class I (all structures) and Class II (single-family detached dwellings only)
Permits
NC requires a mechanical permit for HVAC installation, change-outs, and ductwork modification. Permits are issued by the city or county building inspections office; the contractor's H-class license number is required on the application.
A replacement install typically requires a permit as well.
NC permit reviewers expect a load calculation aligned with the NCECC; confirm with the local AHJ which documentation and software it requires before submittal.
05 · FAQ
Common Manual J questions for North Carolina contractors.
+Which NC heating license do I need for residential HVAC?
H-3. Under G.S. 87-21, systems in single-family residences fall under Heating Group 3 regardless of size, along with other systems of 15 tons or less. H-2 covers systems over 15 tons, and H-1 covers steam and hot-water systems. A Class II license limits the holder to single-family detached dwellings; Class I covers all structures.
+Why does NC span three climate zones?
On the IECC 2015 county map, going from coast to mountains, the state covers zone 3A (Charlotte and southeastern NC), zone 4A (Triangle, Triad, and most of the Piedmont; the IECC 2021 map moves Wake, Durham, and Guilford to 3A), and zone 4A/5A in the Appalachian highlands (Asheville sits in 4A; Boone and Mount Mitchell touch 5A). Manual J winter design temps vary by 12°F across the state.
+Does NC require Manual J for a residential permit?
Yes - NCECC requires HVAC equipment to be sized per Manual J or equivalent. Documentation requirements vary by AHJ. BuildSolver is not ACCA-approved for permit submission. Use its output for sales-phase sizing and client quotes, and produce the permit submittal in ACCA-approved software such as Wrightsoft Right-J8 or Cool Calc Manual J.
+How does Charlotte's design temp compare to Raleigh?
Charlotte (zone 3A) designs to 94°F summer DB and 22°F winter. Raleigh (zone 4A on the IECC 2015 county map; 3A on the IECC 2021 map that BuildSolver's calculator uses for Wake County ZIP codes) designs to 93°F summer DB and 20°F winter. Cooling design is very similar, but Raleigh's winter design is slightly colder, so Manual J heating loads for Raleigh typically run 5-8% higher per square foot than Charlotte for the same building.
+What's the average NC HVAC wage?
BLS OEWS May 2025 (released May 15, 2026) reports a $27.53/hr median for North Carolina HVAC mechanics and installers, with an annual mean of $57,400. The national median is $29.33/hr.
+How often does the NC H-class license need renewal?
Annually. The board eliminated mandatory continuing education in 2012, so annual renewal no longer requires CE hours.
Try a North Carolina load calculation now.
The chat will ask follow-up questions like an experienced engineer - square footage, construction type, window count, insulation level - and run the Manual J on your inputs. Outdoor design conditions come from its own dataset (by IECC 2021 climate zone for a ZIP code, by weather station for the 10 major metros in its city list), not from the metro table on this page.
Start North Carolina calculationRelated · same climate zone
Other states with similar ASHRAE climate zones.
Climate-driven Manual J inputs such as infiltration, latent share, and design temperatures behave similarly across states that share a climate zone. Each page below gives that state's own design temperatures and licensing context. Zones combine the IECC 2015 and IECC 2021 county maps.
Data last reviewed October 7, 2026 · underlying sources as of May 15, 2026