HVAC Load Calculation Check
Check two inputs of any Manual J: the outdoor design temperatures for your county, and whether the equipment fits the load it calculated.
Updated October 26, 2026
County limits from EPA's ENERGY STAR guide (2019 Edition, 3,146 entries); sizing limits from the ENERGY STAR National HVAC Design Report, revised January 15, 2025.[1][2]
Design temperatures for your county
Equipment size vs the Manual J load
From the Manual J report.
Needed for heat pumps, to test for a Condition B climate.
From card 1, or type it.
From the manufacturer's expanded performance data at your design conditions. Two-speed: maximum compressor speed. Variable-speed: the AHRI rating speed.[2]
From the Manual J report.
Two-stage and modulating furnaces: the maximum output.[2]
ENERGY STAR limits the outdoor design temperatures a Manual J may use, county by county: no hotter than the county's 1% cooling value and no colder than its 99% heating value. For Travis County, Texas, that is 99°F (37°C) for cooling and 28°F (−2°C) for heating.[1]
An air conditioner sized from a Manual J is only right if the Manual J used the right weather. A design temperature a few degrees too hot for cooling, or too cold for heating, makes the calculated load bigger, and the equipment sized to it bigger too.
EPA's ENERGY STAR program publishes design-temperature limits for 3,146 counties, county equivalents and territories, and its HVAC design report sets how far equipment capacity may exceed the calculated load. This page puts both in one place, with the weather stations EPA used for each county.
How EPA set each county's limit
EPA drew on two sets of weather-station design data: the 1% cooling and 99% heating design temperatures in the ASHRAE 2017 Handbook of Fundamentals, and the design conditions in ACCA's Manual J, 8th Edition. In the guide, (A) marks an ASHRAE station and (M) a Manual J station.[1]
For each county, EPA took the highest cooling temperature, the lowest heating temperature and the highest HDD/CDD ratio among the stations inside the county or within 40 miles (64 km) of its geographic center. Where no station was that close, it averaged the nearest three and listed all three.[1]
Cooling limits were rounded up to a whole degree and heating limits rounded down. A cooling limit below 80°F (27°C) was raised to 80°F; that applies to 38 entries, including all 28 in Alaska.[1]
Each number is an outer bound. EPA recommends the Manual J 8th Edition 1% cooling and 99% heating temperatures for the weather station closest to the home, and temperatures set by the local jurisdiction take precedence over the table.[1]
The table applies to homes certified through ENERGY STAR's National HVAC Design Report; projects graded under ANSI/RESNET/ACCA/ICC 310 use the limits in that standard's Appendix A.[3]
Indoor conditions, people and appliances
ENERGY STAR's design report sets the indoor side at 70°F (21°C) for heating and 75°F (24°C) for cooling.[2] ACCA's checklist for reviewing a Manual J uses the same temperatures and adds humidity: 30% relative humidity in winter and 50% in summer, or 55% in humid climates and 45% in dry ones, unless local code sets other values.[4]
The checklist counts occupants as bedrooms plus one, at 230 Btu/h (67 W) sensible and 200 Btu/h (59 W) latent per person, so a three-bedroom house carries four people: 920 Btu/h sensible and 800 Btu/h latent. Appliance gain is 1,200 or 2,400 Btu/h (352 or 703 W), or a value Manual J recommends.[4]
A report that uses a lower cooling setpoint, more occupants or a larger appliance allowance shows a larger cooling load than these values give. To see what 75°F at 50% relative humidity means for dew point, use the psychrometric calculator.
How much bigger than the load the equipment can be
ENERGY STAR divides the equipment's total cooling capacity at the design conditions, taken from the manufacturer's expanded performance data, by the Manual J maximum total heat gain. For two-speed equipment the capacity is at the maximum compressor speed; for variable-speed equipment, at the AHRI rating speed.[2]
| Equipment | Recommended | Allowed |
|---|---|---|
| Single-speed | 90–115% | 90–130% |
| Two-speed | 90–120% | 90–140% |
| Variable-speed | 90–130% | 90–160% |
| Heat pump in a Condition B climate, any compressor | from 90% of the load to the load plus 15,000 Btu/h (4.4 kW) | |
Source: ENERGY STAR Single-Family New Homes National HVAC Design Report, Rev. 14 (revised January 15, 2025), Item 4.15.
The recommended ranges follow ACCA Manual S, Second Edition; the report calls the wider allowed ranges a temporary allowance above the Manual S limits.[2]
A heat pump is in a Condition B climate when the home's load sensible heat ratio (sensible heat gain divided by total heat gain) is 95% or more and the location's HDD/CDD ratio is 2.0 or more; the ratio comes from the county table above.[2] 1,242 of the 3,146 entries have a ratio of 2.0 or more.[1]
For small loads ENERGY STAR also accepts a single-speed system of up to 20,000 Btu/h (5.9 kW) when the total cooling load is 15,000 Btu/h (4.4 kW) or less, and a two-speed or variable-speed system of up to 25,000 Btu/h (7.3 kW) when the load is 18,000 Btu/h (5.3 kW) or less.[2]
Furnaces are sized on output: 100–140% of the total heat loss when the furnace only heats; paired with cooling, 100–140% recommended and up to 400% allowed. Two-stage and modulating furnaces count their maximum output. The report sets no heating limit for heat pumps and records their heating capacity at 17°F (−8°C) and 47°F (8°C).[2]
Once the equipment is chosen, the duct size calculator sizes the runs for its airflow.
ENERGY STAR's recommended cooling capacity for a single-speed air conditioner or heat pump in a Condition A climate, as a share of the Manual J load. Source: ENERGY STAR National HVAC Design Report, Rev. 14, Item 4.15.
Checking a Manual J report, line by line
ACCA publishes a checklist for reviewing a Manual J. Paraphrased, it asks:[4]
- Design temperatures: indoor as above; outdoor from Manual J Table 1 or local code.
- Windows and glass doors: U-factor and SHGC checked against Manual J Table 2, shading and overhangs counted, areas and directions matching the plans.
- Skylights: the same checks as windows.
- Walls: insulation R-values and wall areas that match the plans.
- Ceilings: insulation R-value, a radiant barrier only if one is installed, roof color and material, and ceiling area.
- Floors: insulation and construction type as built or planned.
- Infiltration: a tightness rating on the scale tight, semi-tight, average, semi-loose, loose, and the above-grade volume from the plans.
- Internal gains: appliances, occupants and per-person gains as above.
- Ducts: insulation where ducts run through unconditioned space, and sealing rated average or better.
- Ventilation: intermittent bath and kitchen fans left out of infiltration, continuous exhaust fans included, plus any heat-recovery ventilator or ventilating dehumidifier.
Every applicable item should be a yes for the load to represent the house.[4]
Why there's no square-foot estimate here
A Manual J load depends on the items in that checklist: window and skylight ratings and areas, insulation, air tightness, duct location and ventilation. A tons-per-square-foot figure leaves all of them out, and ENERGY STAR's sizing limits are percentages of the Manual J load, so this page checks a load calculation instead of replacing one.[2]
Example: a home in Travis County, Texas
EPA's guide uses Travis County as its own example. The county's limits are 99°F (37°C) for cooling and 28°F (−2°C) for heating, and its HDD/CDD ratio of 0.3 is below 2.0, so a heat pump there would use the Condition A limits.[1]
Say the home's Manual J shows a maximum total heat gain of 30,000 Btu/h (8.8 kW), and the single-speed air conditioner under consideration delivers 34,500 Btu/h (10.1 kW) at the design conditions in its expanded performance data. That is 115% of the load, the top of the recommended 90–115% range; a model delivering 38,000 Btu/h (11.1 kW) would be 126.7%, above the recommended range and inside the allowed 90–130%.[2]
With a furnace and a Manual J heat loss of 40,000 Btu/h (11.7 kW), a furnace with 56,000 Btu/h (16.4 kW) of output is 140%, the top of the recommended range for a furnace paired with cooling.[2]
Design-temperature limits by state
The range of county limits in each state and territory, from the same EPA table.[1]
| State or territory | Counties listed | Cooling limits (°F) | Heating limits (°F) | Ratio 2.0 or more |
|---|---|---|---|---|
| Alabama | 67 | 91–97 | 16–30 | 0 |
| Alaska | 28 | 80 | −46–20 | 28 |
| Arizona | 15 | 97–116 | −13–27 | 4 |
| Arkansas | 75 | 93–100 | 14–26 | 0 |
| California | 58 | 88–118 | −13–33 | 33 |
| Colorado | 64 | 80–99 | −14–9 | 51 |
| Connecticut | 8 | 89 | 0–7 | 8 |
| Delaware | 3 | 91 | 11–18 | 0 |
| District of Columbia | 1 | 94 | 14 | 0 |
| Florida | 67 | 91–97 | 27–48 | 0 |
| Georgia | 159 | 89–97 | 18–32 | 0 |
| Guam | 1 | 89 | 74 | 0 |
| Hawaii | 5 | 85–90 | 31–62 | 1 |
| Idaho | 44 | 84–97 | −11–15 | 42 |
| Illinois | 102 | 90–95 | −4–15 | 38 |
| Indiana | 92 | 89–94 | −1–12 | 51 |
| Iowa | 99 | 87–93 | −21–1 | 84 |
| Kansas | 105 | 92–101 | 2–12 | 0 |
| Kentucky | 120 | 84–95 | 5–18 | 0 |
| Louisiana | 64 | 92–98 | 24–35 | 0 |
| Maine | 16 | 80–87 | −18–7 | 16 |
| Maryland | 24 | 90–94 | 4–20 | 1 |
| Massachusetts | 14 | 82–90 | −3–12 | 14 |
| Michigan | 83 | 80–90 | −14–9 | 83 |
| Minnesota | 87 | 80–90 | −21–−6 | 87 |
| Mississippi | 82 | 92–97 | 19–29 | 0 |
| Missouri | 115 | 91–98 | 0–17 | 4 |
| Montana | 56 | 80–95 | −18–7 | 56 |
| Nebraska | 93 | 91–99 | −8–5 | 61 |
| Nevada | 17 | 91–116 | −16–17 | 16 |
| New Hampshire | 10 | 84–90 | −18–0 | 10 |
| New Jersey | 21 | 90–92 | 3–13 | 6 |
| New Mexico | 33 | 83–101 | 1–25 | 12 |
| New York | 62 | 83–92 | −12–10 | 60 |
| North Carolina | 100 | 87–95 | 12–31 | 0 |
| North Dakota | 53 | 83–97 | −20–−9 | 53 |
| Northern Mariana Islands | 1 | 90 | 75 | 0 |
| Ohio | 88 | 87–92 | 1–10 | 65 |
| Oklahoma | 77 | 97–104 | 9–25 | 0 |
| Oregon | 36 | 80–96 | 2–35 | 28 |
| Pennsylvania | 67 | 84–91 | 2–11 | 55 |
| Puerto Rico | 1 | 90 | 68 | 0 |
| Rhode Island | 5 | 87–88 | 2–9 | 5 |
| South Carolina | 46 | 90–97 | 18–30 | 0 |
| South Dakota | 66 | 87–97 | −21–−1 | 66 |
| Tennessee | 95 | 85–97 | 12–22 | 0 |
| Texas | 254 | 91–104 | 11–40 | 0 |
| Utah | 29 | 84–109 | −4–12 | 27 |
| Vermont | 14 | 84–87 | −18–−4 | 14 |
| Virgin Islands, U.S. | 1 | 89 | 70 | 0 |
| Virginia | 134 | 85–95 | 7–23 | 11 |
| Washington | 39 | 80–98 | 0–29 | 33 |
| West Virginia | 55 | 85–93 | 4–15 | 24 |
| Wisconsin | 72 | 82–91 | −16–0 | 72 |
| Wyoming | 23 | 80–95 | −13–1 | 23 |
Source: EPA ENERGY STAR Design Temperature Limit Reference Guide (2019 Edition), Exhibit 1. Counties listed include county equivalents such as parishes, boroughs and independent cities.
Sources
- [1]U.S. EPA, ENERGY STAR — Design Temperature Limit Reference Guide (2019 Edition): ENERGY STAR Single-Family New Homes Rev. 11 and Multifamily New Construction Rev. 02, Exhibit 1, pages 4–141. U.S. EPA, ENERGY STAR. revised April 27, 2021. https://www.energystar.gov/sites/default/files/asset/document/Design%20Temperature%20Limit%20Reference%20Guide%20%282019%20Ed%29%20-%20ENERGY%20STAR%20SFNH%20Rev11_MFNC%20Rev02.pdf (accessed October 26, 2026)
- [2]U.S. EPA, ENERGY STAR — Single-Family New Homes National HVAC Design Report, Version 3.1 / 3.2 / 3.3 (Rev. 14). U.S. EPA, ENERGY STAR. revised January 15, 2025. https://www.energystar.gov/sites/default/files/2025-01/National%20HVAC%20Design%20Report_Rev%2014.pdf (accessed October 26, 2026)
- [3]U.S. EPA, ENERGY STAR — HVAC Designers (residential new construction partner resources). U.S. EPA, ENERGY STAR. https://www.energystar.gov/partner_resources/residential_new/working/hvac/hvac_designers (accessed October 26, 2026)
- [4]Air Conditioning Contractors of America (ACCA Code Committee) — Verifying ACCA Manual J Procedures (load calculation checklist brochure); copy hosted by the Montana Department of Environmental Quality. ACCA. https://deq.mt.gov/files/Energy/EnergizeMT/Conservation/Energy%20Code/ACCAManual-J-Brochure.pdf (accessed October 26, 2026)
County limits: EPA guide revised April 27, 2021. Sizing limits: ENERGY STAR report revised January 15, 2025. Checked October 26, 2026.
How to read your results
- Cooling limit
- The hottest outdoor temperature a Manual J for that county may use under ENERGY STAR. A report that uses a hotter one overstates the cooling load.
- Heating limit
- The coldest outdoor temperature it may use. A colder one overstates the heat loss.
- HDD/CDD ratio
- Heating degree days divided by cooling degree days for the station EPA picked. At 2.0 or more, a heat pump can use the Condition B limit when the home's load sensible heat ratio is 95% or more.
- Stations
- The weather stations behind each number. (A) is an ASHRAE station and (M) a Manual J station; an asterisk after a station name means the 80°F floor set the cooling limit.
- Cooling sizing
- Capacity at design conditions divided by the maximum total heat gain. Recommended follows ACCA Manual S, Second Edition; allowed is ENERGY STAR's temporary allowance above it.
- Furnace sizing
- Output divided by the total heat loss, 100–140% for heating only, and up to 400% allowed when paired with cooling.
Related tools
Frequently asked
›What outdoor design temperature should a Manual J use?
The local jurisdiction's value, if it sets one. Otherwise EPA recommends the Manual J 8th Edition 1% cooling and 99% heating temperatures for the weather station closest to the home, and for ENERGY STAR homes they may not be hotter or colder than the county limits in EPA's guide.[1]
›How much can an air conditioner be oversized?
Under ENERGY STAR, a single-speed unit's capacity at design conditions should be 90–115% of the Manual J total heat gain and may go to 130%. Two-speed units: 90–120%, up to 140%. Variable-speed units: 90–130%, up to 160%.[2]
›What is a Condition B climate?
A location where the home's load sensible heat ratio is 95% or more and the HDD/CDD ratio is 2.0 or more. There, a heat pump's cooling capacity may run from 90% of the load to the load plus 15,000 Btu/h (4.4 kW).[2]
›How many people does Manual J count?
One per bedroom plus one, at 230 Btu/h (67 W) sensible and 200 Btu/h (59 W) latent each, according to ACCA's review checklist.[4]
›How big can a furnace be compared with the heat loss?
100–140% of the Manual J total heat loss for a furnace that only heats. Paired with cooling, ENERGY STAR recommends 100–140% and allows up to 400%. Two-stage and modulating furnaces count their maximum output.[2]
›Why doesn't this page estimate tons from square footage?
A Manual J load depends on windows, insulation, air tightness, ducts and ventilation, which floor area doesn't capture, and ENERGY STAR's sizing limits are percentages of that load. Run a Manual J, or ask for the one your contractor ran, and check it here.[2]