Florida Keys: energy calcs & Manual J.
A 55°F heating design: the mildest winter in Florida’s data.
Monroe County, the Florida Keys, has the mildest heating design limit in the state, 55°F, with a 91°F cooling limit, both from Marathon. It is climate zone 1A. Heating barely registers, so a Keys Manual J is a cooling and latent problem. We haven't verified Monroe's or the island cities' submittal checklists yet.
- Counties
- 1 countyMonroe
- Departments
- Each county’s ownSeveral cities run their own · what we publish
- Code edition
- FBC Energy Conservation, 8th Ed. (2023)9th Ed. (2026) scheduled for Dec 31, 2026 · what changes
- Price
- $195 · $445 · $595Energy calc from · full package · sealed. Same in all 67 counties · price list
- Ready by
- 2–3 business daysExpedited: within 24 business hours, +$150. Clock starts when complete plans pass intake (3:00 PM ET cutoff) · how it works
Monroe
Per-county table1 counties · zone, design °F, permits, housing
What it means for sizing
2 paragraphs · design temperatures, housing stock, equipment
Marathon supplies both of Monroe's limits: 91°F cooling from Marathon Airport and 55°F heating from the Florida Keys Marathon station.2 Monroe is one of seven zone 1A counties.1 Our reading: with a 55°F design, the heating line on a Manual J is small enough that equipment selection turns entirely on sensible and latent cooling, and the dehumidification capacity of the coil deserves as much attention as tonnage.
Monroe's housing is older and smaller than the state's: a 1982 median, 45.6% built before 1980 and a 4.3-room median, tied with Miami-Dade for the smallest we've recorded.4 The county issued 239 one-unit permits in 2025.3 Check with the local building department for its flood-zone requirements; this hub carries the design data.
Worked example
1,400 sq ft house in Monroe County → 18,750 Btu/h, 1.56 tons · illustrative
Illustrative · not a Manual J
A 1,400 sq ft two-bedroom house at Marathon's 91°F and 55°F limits. The 55-grain moisture difference is our assumption for an island site, and it is why the latent line is large relative to the house.
| House | new elevated single-storey frame home, Marathon |
|---|---|
| Conditioned area | 1,400 sq ft, 1 storey, 9 ft ceilings |
| Bedrooms / occupants | 2 / 3 |
| Glazing | 15% of floor area (210 sq ft), U 0.3, SHGC 0.25 |
| Walls / ceiling | R-13 walls, R-38 ceiling under a vented attic |
| Air leakage | 5 ACH50 |
| Ducts | in the attic, 8% gain allowance |
| Outdoor design | 91°F cooling / 55°F heating (Monroe County, sourced) |
| Indoor design | 75°F cooling / 70°F heating |
| Design grains difference | 55 gr/lb (assumption) |
Illustrative only. A simplified block-load estimate with the inputs shown, not an ACCA Manual J, and not for permitting. A real calc goes room by room with your plans, orientation and equipment data.
Building departments
How we publish department checklists
Every county here has its own building department, and several cities run their own. We publish a department's checklist, contacts and quirks only after reading them on its official page, and each county here gets its own page once that's done. Until then, check with the county building department before you submit. Ordering works statewide today.
Florida Keys questions
3 answers · What heating design temperature applies in the Florida Keys?
What heating design temperature applies in the Florida Keys?
55°F at 99% heating, from the Florida Keys Marathon station, the mildest heating limit assigned to any Florida county in RESNET's table. Cooling is 91°F, from Marathon Airport. With heating that mild, the Manual J focuses on sensible and latent cooling.
Is Monroe County climate zone 1A?
Yes. Table R301.1 of the 8th Edition energy code lists Monroe as zone 1A, warm-humid, alongside Broward, Collier, Hendry, Lee, Miami-Dade and Palm Beach. The zone sets the prescriptive values an R402 must meet and the baseline an R405 is compared against.
Why isn't there a full Monroe County page?
We publish county pages only after reading a county's own permit checklists and confirming its building departments, and the Keys have several. Those aren't verified yet, so this page carries only sourced design and housing data. Orders from Monroe are priced the same as everywhere in Florida.
Nearby and related
Price
One statewide price in all 67 counties. Building departments decide what they accept; we don’t guarantee approval. Revisions for plan-review comments on the same design are free.
Sources
4 primary references · numbered to match the citations
- 012023 Florida Building Code, Energy Conservation (8th Ed.), Table R301.1, climate zones by countyup.codes
- 02RESNET / ENERGY STAR, Appendix A: HVAC Design Temperature Limits by State and County (v4, 2019)resnet.us
- 03U.S. Census Bureau, Building Permits Survey, 2025 annual county data (new privately-owned 1-unit housing units)www2.census.gov
- 04U.S. Census Bureau, American Community Survey 2020–2024 5-year estimates (B25001, B25003, B25018, B25024, B25034, B25035, B25040), via Census Reportercensusreporter.org