3.2 Additional Energy Efficiency Packages (R401.2.5, R408)

3.2 Additional Energy Efficiency Packages (R401.2.5, R408)

Quick Answer: Every 2021 residential path must satisfy R401.2.5. Prescriptive jobs install one R408.2 package. Performance jobs either install one R408.2 package without including those measures in the R405 proposed design, or show proposed annual energy cost ≤ 95% of the standard reference design. ERI jobs must come in at least 5 percent less than Table R406.5. Identify the option on the R401.3 certificate.

Section R401.2.5 is the sentence that turns a 2018-style "pick a path" review into a 2021 review. It establishes additional requirements applicable to all compliance approaches. Independent OpenExamPrep teaching for Exam 79 treats the section as a plans-examiner checklist item: if the energy sheet never says how R401.2.5 is met, the primary path is unfinished.

How R401.2.5 maps onto each path

Prescriptive (R401.2.1). One of the additional efficiency package options shall be installed according to Section R408.2. Not two packages, not half a package, and not a promise to "maybe add an HRV." The drawings should name the package by section (for example, R408.2.3 reduced service water-heating energy) and show the equipment or envelope numbers that meet that section.

Performance (R401.2.2). The building shall meet one of the following:

• One of the additional efficiency package options in R408.2 shall be installed without including such measures in the proposed design under R405; or
• The proposed design of the building under R405.2 shall have an annual energy cost that is less than or equal to 95 percent of the annual energy cost of the standard reference design.

The first performance method is an installed package that the energy model is not allowed to take credit for. If the R408 measure is a 16 SEER air conditioner, the R405 proposed design cannot also claim that 16 SEER as the reason the annual cost already looks good, and then count the same unit as the R401.2.5 package. The second method is a 5 percent cost stretch against the standard reference design, with no R408 package required.

ERI (R401.2.3). The Energy Rating Index value shall be at least 5 percent less than the Energy Rating Index target specified in Table R406.5. Work the arithmetic on the 2021 table, not on a remembered 2018 number. Climate Zone 5's Table R406.5 target is 55, so 5 percent less is 55 × 0.95 = 52.25. An ERI of 55 meets the table and still fails R401.2.5. Climate Zone 4's table target is 54 (54 × 0.95 = 51.3). Climate Zones 0 through 2 use 52 (52 × 0.95 = 49.4). Do not substitute practice-bank question counts or older 57/55/53 folklore for Table R406.5.

The option selected for compliance shall be identified in the certificate required by Section R401.3. A passing blower-door sticker in the furnace closet does not identify whether the project used an R408 package, a 95 percent cost showing, or a 5 percent ERI reduction.

The five R408.2 packages

R408.1 states that the section establishes additional efficiency package options to achieve additional energy efficiency in accordance with R401.2.5. R408.2 then sets the options out in R408.2.1 through R408.2.5. Although R408.2's lead-in mentions compliance with R401.2.1, R401.2.5 also uses these same packages on the performance path. Teach the 2021 thresholds as written; they are not "better than code" slogans.

Package-by-package review notes

R408.2.1 Enhanced envelope. This is stricter than ordinary Total UA. Ordinary R402.1.5 allows proposed UA up to 100 percent of Table R402.1.2 UA. The package caps UA at 95 percent of that same table UA and also tightens glazed SHGC to 95 percent of the table SHGC. In Climate Zone 4 except Marine, Table R402.1.2 SHGC is 0.40, so 95 percent is 0.38. The UA calculation is performed in accordance with R402.1.5, which means same assembly areas, ASHRAE Handbook of Fundamentals methods, and framing thermal bridging. A REScheck-style printout that only shows 100 percent UA does not prove this package.

R408.2.2 More efficient HVAC. The gas-furnace option is a pair: 95 AFUE and 16 SEER cooling. A 95 AFUE furnace with a 13 SEER condenser is not the package. An air-source heat pump must meet both 10 HSPF and 16 SEER. A ground-source heat pump must meet 3.5 COP. Multiple-system language is an exam favorite: a 16 SEER air handler on the second floor plus an old-efficiency basement unit that still serves part of the load fails, because all systems must meet the minimum and be sized to 100 percent of the respective design load. Nameplate efficiencies on installed equipment must match the approved package.

R408.2.3 Reduced water-heating energy. The 2021 text uses energy factor (EF), not a UEF conversion invented at the counter. Fossil fuel ≥ 0.82 EF, electric ≥ 2.0 EF, or solar fraction ≥ 0.4. A 0.62 EF gas tank with a "solar-ready" roof rack and no collectors is not a 0.4 solar fraction. Heat-pump water heaters typically satisfy the 2.0 EF electric option when the listed EF is at least 2.0; the inspector still reads the nameplate rather than assuming the product class.

R408.2.4 Efficient ducts. Three different location rules, not one attic slogan. Option 1 is 100 percent of ducts and air handlers entirely within the building thermal envelope. An air handler in a vented attic kills option 1 even if every trunk is buried. Option 2 is 100 percent ductless or hydronic distribution completely inside the envelope (minisplits or a boiler loop with no duct system). Option 3 is 100 percent of the duct system in conditioned space as defined by R403.3.2, which is not automatically the same as "inside the thermal envelope." Chapter 9 works R403.3.2; on this chapter, do not treat the three bullets as synonyms.

R408.2.5 Air sealing plus ventilation. Two halves, both required: measured leakage ≤ 3.0 ACH50 and an ERV or HRV that meets the recovery and fan metrics. A 3.0 ACH50 house with a bath fan is not this package. SRE is at least 75 percent, fan energy is not more than 1.1 W/CFM, and recirculation shall not be used as a defrost strategy. ERVs add LRMT of at least 50 percent. Ratings are taken at the lowest tested net supply airflow. A unit that meets SRE only at a high-speed test point and drops below 75 percent at the airflow used for compliance does not meet the package.

Plans examiner and inspector workflow

On the drawings, find a single R401.2.5 sentence. If the path is prescriptive, it should cite one R408.2 subsection and the matching equipment or envelope values. If the path is performance, it should either list the R408 package and state that those measures are excluded from the proposed design, or show proposed annual energy cost ≤ 95 percent of the standard reference design. If the path is ERI, it should show Table R406.5, the 5 percent reduction, and the rated index.

In the field, inspect the package that was approved, not a more expensive substitute that was never submitted. Swapping a 3.5 COP ground-source heat pump for the approved R408.2.1 envelope package is a path change. It may be approvable after a revision, but it is not a field trade.

Scenario. A performance project models a 16 SEER / 10 HSPF heat pump in the R405 proposed design and also lists R408.2.2 as the R401.2.5 method. That double-counts the measure. Either remove the package credit from the proposed design, pick a different R408 package that is not in the model, or drop the package and show annual energy cost at or below 95 percent of the standard reference design.

Scenario. An ERI project in Climate Zone 3 posts an index of 51. Table R406.5 for Climate Zone 3 is 51. R401.2.5 requires at least 5 percent less than 51, which is 48.45. An index of 51 meets the table and fails the overlay. Ask for a revised rating or a different primary path.

Do not describe these packages as official ICC approval of a product line. They are 2021 IECC residential thresholds that OpenExamPrep teaches for Exam 79 study.