34.3 Energy Forms, R/U Factors, Window Heat Gain & Florida Load Calcs

34.3 Energy Forms, R/U Factors, Window Heat Gain & Florida Load Calcs

Trade H items 3 and 4 are office work that still fail people in the field: complete energy forms (software, R/U, thermal resistance) and perform load calculations (building-material R/U, window heat gain, outdoor air change, Florida energy codes, heating and cooling loads, thermal resistances). Chapter 16 taught the Trade A math. This section is how that math lands on a permit form and how annual R405 loads differ from peak Manual J tons.

Quick Answer: Pick a R401.2 path. Print the matching 2023 form — R402 prescriptive, R405 performance, or R406 ERI — from Florida Building Commission-approved software (EnergyGauge USA for residential 2023). R405.3 requires proposed normalized Modified Loads ≤ 95 percent of the standard-reference annual loads. Attach the EPL card (F.S. 553.9085). Size the equipment with Manual J / Manual S at 75°F cooling / 72°F heating. Do not type 7 ACH50 into the infiltration line.

Which form, which software

R401.2 Compliance — one of:

1. Prescriptive R401 through R404 → Form R402-2023 (and the UA alternative if you use R402.1.5).
2. R405 simulated performance plus every provision labeled Mandatory → Form R405-2023.
3. Energy rating index R406 → Form R406-2023.

Commercial buildings use the [CE] half of the same code and Form C402-2023 (and related commercial compliance reports). Appendix RD is the official forms appendix.

R405.4.1 Compliance software tools: computer software used to demonstrate compliance shall have been approved by the Florida Building Commission. DBPR’s energy-code page lists EnergyGauge USA (FSEC / University of Central Florida) for Residential, 8th Edition 2023. Other tools may generate a legal Form R405-2023 only if the Commission has approved that tool and version. A contractor-built spreadsheet named after a salesperson is not a compliance report.

R405.3 Performance-based compliance: the proposed residence must show annual total normalized Modified Loads ≤ 95 percent of the annual total loads of the standard reference design (Appendix RC). That 95 percent is a whole-building annual test. It is not the Manual S 1.15 peak-capacity cap, and it is not a license to skip Mandatory items (blower door, EPL card, R403.7 sizing, thermostat rules).

R405.4.2: submit a proposed-design compliance report with the permit application. Before certificate of occupancy, submit an as-built compliance report. If the house is offered in multiple orientations, the tool may document all four cardinal orientations or a worst-case rotation. Claiming “worst case = no” on the form when the model was only run facing north is how west glass shows up later as a humidity complaint.

R401.3 Energy Performance Level (EPL) display card (Mandatory) and F.S. 553.9085: the building official requires a completed EPL card, certified accurate by the builder, before occupancy. The card is an addendum to each sales contract for presold and non-presold residential buildings. It lists component efficiencies (glass U and SHGC, wall and ceiling R, duct location and R, cooling SEER2, heating, water heating, HVAC credits such as ceiling fans, cross ventilation, programmable thermostat, multizone). If installed features change, complete a new EPL card.

A typical R405-2023 documentation checklist (Appendix RD / local permit packets) includes:

Energy Efficient Building Construction in Florida (2024) is the textbook that walks these forms, climate, moisture, and attic-duct practice. Use it with the code, not instead of the form.

R-value, U-factor, and what you type where

(U = 1 / R_{\text{total}}). Series resistances add. Do not add U-factors of stacked layers.

R402.1.3 (prescriptive R on Form R402 / Table R402.1.2): sum insulation layers only. Do not include gypsum, sheathing, or air films. Blown insulation uses the manufacturer's settled R. Insulated siding used as continuous insulation is reduced R-0.6 from the labeled value. Climate Zone 2 wood-frame wall R-13 on the form means R-13 of cavity insulation, not R-13 including drywall.

Load-calculation assembly U (Manual J / Standard 183) does include inside film, gypsum, cavity, sheathing, siding, outside film, and framing (parallel paths). Table R402.1.4 equivalent U-factors already include bridging (Climate Zone 2 frame wall U-0.084, ceiling U-0.030, fenestration U-0.40). Using insulation-only 1/13 = 0.077 as a wall U both mis-scores the form and mis-sizes the equipment.

Worked series R (cavity path, for the load — not for Table R402.1.2). Summer outside film 0.25 + 1/2 in. siding 0.81 + 1/2 in. plywood 0.62 + R-13 batt + 1/2 in. gypsum 0.45 + inside film 0.68 = R-total 15.81, U = 0.0633 Btu/h·ft²·°F. At R302.1 indoor cooling 75°F and a 95°F example outdoor (replace 95°F with the site ACCA Table 1A or ASHRAE 1% value on a real job):

(Q = U \times A \times \Delta T = 0.0633 \times 450 \times 20 \approx 570\ \mathrm{Btu/h})

That 450 ft² cavity-path wall is still not the framed UA. R402.1.5 Total UA compares (\sum U A) to Table R402.1.4 U-factors times the same areas; SHGC still must be met.

Florida rows you actually type (Table R402.1.2 / R402.1.4), Climate Zones 1 and 2 only:

• Zone 1 (Broward, Collier, Hendry, Lee, Miami-Dade, Monroe, Palm Beach): ceiling R-30, wood-frame wall R-13, fenestration U NR, skylight U 0.75, SHGC 0.25, ceiling U-factor alt. 0.035, frame-wall U 0.084.
• Zone 2 (every other Florida county): ceiling R-38, wall R-13, fenestration U 0.40 (0.65 if impact-rated, footnote j), skylight U 0.65, SHGC 0.25, ceiling U 0.030, frame-wall U 0.084.

Window heat gain — the Florida-dominant term

Glass load has two pieces. Conduction uses NFRC U-factor:

(Q_{\text{cond}} = U \times A \times \Delta T)

Solar heat gain uses SHGC (and Manual J interior shade, overhang projection, orientation, and glass-load factors). A teaching peak-solar form is:

(Q_{\text{solar}} \approx A \times \mathrm{SHGC} \times I \times \text{shade factors})

where (I) is incident solar (Btu/h·ft²) at the hour you care about. Table R402.1.2 glazed fenestration SHGC is 0.25 in both Zone 1 and Zone 2. Zone 1 vertical fenestration U is NR; SHGC is not NR.

Worked glass. 40 ft² of west glass, SHGC 0.25, U 0.40, ΔT 20°F, peak incident solar 200 Btu/h·ft² (clear August west hour used as a classroom peak — Manual J tables replace this on a permit):

• Conduction: (0.40 \times 40 \times 20 = 320) Btu/h
• Solar: (40 \times 0.25 \times 200 = 2{,}000) Btu/h

Solar is six times conduction on that lite. Raise SHGC to 0.40 and solar becomes 3,200 Btu/h. That is why west glass and SHGC move a Florida R405 run and a Manual J total more than arguing R-30 versus R-38 on an already insulated ceiling. Overhang projection factor (depth / height above the sill) is a real form input; the tropical-zone path even treats PF ≥ 0.30 as an SHGC alternative.

Outdoor air change and the two different “ACH” numbers

Infiltration is uncontrolled envelope leakage. Ventilation is outdoor air you intend to bring in. Peak air-side loads (standard air):

(\mathrm{CFM} = (\mathrm{ACH} \times V) / 60)

(Q_s = 1.08 \times \mathrm{CFM} \times \Delta T)

(Q_l = 0.68 \times \mathrm{CFM} \times \Delta \text{grains})

7 ACH50 is the blower-door cap. Natural ACH for the load is a small fraction of that (order of ACH50/15–20). R403.6.2 then caps mechanical ventilation at the ASHRAE 62.2 design air-change minimums as maxima. Do not add (a) 7 ACH as if it were continuous, (b) the bath fan, and (c) whole-house ERV CFM as three independent peak outdoor-air streams. Intermittent kitchen and bath exhaust stays out of the R403.7 sizing load.

Worked air change. 2,000 ft², 8 ft, (V = 16{,}000) ft³. Natural infiltration modeled at 0.35 ACH after converting a legal envelope toward design leakage: CFM = (0.35 \times 16{,}000 / 60 = 93) cfm. Sensible infiltration at ΔT 20°F: (1.08 \times 93 \times 20 \approx 2{,}010) Btu/h. The blower-door limit on that house is CFM50 = ((7 \times 16{,}000) / 60 = 1{,}867) cfm — a test fan reading, not 1,867 cfm of outdoor air at peak design.

Peak loads vs annual form loads

Residential sizing (Mandatory R403.7.1): ACCA Manual S from ACCA Manual J (or approved equal), directional orientation, indoor conditions R302.1 / C302.1 (72°F heating maximum, 75°F cooling minimum). No designer safety factors, no future-expansion pad, no intermittent kitchen/bath exhaust in the sizing load. Cooling-only total capacity between the calculated total load and 1.15 times that load, or the closest manufacturer size, with latent ≥ calculated latent (R403.7.1.1). Heat pumps follow the cooling 1.15 cap even if heating is larger (R403.7.1.2.1). AHRI nominal total is not a sizing number.

Commercial-style (FBC Mechanical 2023 Section 312): heating and cooling load calculations using ASHRAE/ACCA Standard 183 (or approved equal) at Energy Conservation Chapter 3 [CE] conditions. Class B still performs the calc; installing one system over 25 tons or 500,000 Btu is Class A scope.

R405 / EnergyGauge USA then takes those assemblies, SHGC, duct location, leakage (default Qn 0.080 or tested), equipment SEER2, and credits, and reports annual modified loads against the 95 percent reference. A house can pass R405 and still fail Manual S if someone typed a 5-ton into the form that is 1.6 times the peak load. Both documents are required; they answer different questions.

Florida HVAC scenario

Suncoast Comfort permits a 1,900 ft² Orange County (Zone 2A) house on Form R405-2023 from EnergyGauge USA. The first run uses west glass SHGC 0.40, attic ducts at default Qn 0.080, and a 4-ton 14.3 SEER2 unit picked from a square-foot sheet. The performance report fails R405.3 (proposed modified loads above 95 percent of reference). The qualifier drops SHGC to 0.25, claims Qn 0.040 — which now requires a duct leakage test report — and reruns Manual J at 75°F indoor with orientation. Peak total is 28,500 Btu/h (2.4 tons), 1.15 cap 32,775 Btu/h. A 2.5-ton expanded-data match fits; the 4-ton does not. Ceiling R on the form stays insulation-only R-38 (or the R-30-over-the-plate deemed-to-satisfy on the R-value path, which does not apply to UA). The as-built package for CO is the updated Form R405, EPL card, envelope leakage ≤ 7 ACH50, and the duct test they now owe. Class B’s tonnage cap is not in play; the energy forms still are.

Traps: (1) Using unapproved software. (2) Permit R405 then skipping as-built. (3) Typing Table R402.1.2 R-13 as the Manual J wall U. (4) Ignoring SHGC because Zone 1 fenestration U is NR. (5) Setting infiltration to 7 ACH. (6) Treating EnergyGauge annual PASS as Manual S approval. (7) Forgetting the EPL card is a sales-contract addendum, not a shop drawing.