2.4 Enhanced Air Quality (A05), Enhanced Supply Air (A13) & Microbe and Mold Control (A14)
Key Takeaways
- A05 Enhanced Air Quality is worth 4 points and has three parts: enhanced particulate matter (2 points), enhanced organic gases (1 point) and enhanced inorganic gases (1 point).
- A05 Part 1 awards 1 point for PM2.5 at or below 12 ug/m3 with PM10 at or below 30 ug/m3, and 2 points for PM2.5 at or below 10 ug/m3 with PM10 at or below 20 ug/m3.
- A05 Part 2 tightens organic gases to acetaldehyde 140, acrylonitrile 5, benzene 3, caprolactam 2.2, formaldehyde 9, naphthalene 9 and toluene 300 ug/m3; Part 3 sets CO at 7 mg/m3 (6 ppm) and NO2 at 40 ug/m3 (21 ppb).
- A13 Enhanced Supply Air is satisfied by 100% outdoor air, or by partially recirculated air treated with an activated carbon filter plus either a MERV 14 media filter, in-duct UVGI or upper-room UVGI.
- A14 Microbe and Mold Control requires ultraviolet lamps irradiating the cooling coils and drain pans of all central air handling units, with fan coil unit coils either irradiated or openable for inspection and cleaning.
2.4 Enhanced Air Quality (A05), Enhanced Supply Air (A13) & Microbe and Mold Control (A14)
Core Exam Takeaway: A05 Enhanced Air Quality (4 pt) is the "tighter numbers" optimization — it does not concern airflow. A13 Enhanced Supply Air (1 pt / Core 2 pt) governs what is in the supply stream: 100% outdoor air, or recirculated air treated with activated carbon plus MERV 14, in-duct UVGI or upper-room UVGI. A14 Microbe and Mold Control (1 pt / Core 2 pt) puts UV lamps on cooling coils and drain pans. UVGI therefore appears in two features, A13 and A14, and in neither does WELL specify a wavelength or irradiance value.
Feature A05: Enhanced Air Quality — Optimization (4 pt / WELL Core 4 pt)
A05 recognizes buildings that go beyond A01. WELL cites that around 10% of productivity loss in offices can be attributed to health issues from poor indoor air quality, and that premature mortality could fall by up to 15% if $PM_{10}$ dropped from 70 to 20 µg/m³.
A05 Part 1 — Enhanced Thresholds for Particulate Matter (2 pt)
| Particulate matter thresholds | Points |
|---|---|
| $PM_{2.5} \le 12\ \mu\text{g/m}^3$ and $PM_{10} \le 30\ \mu\text{g/m}^3$ | 1 |
| $PM_{2.5} \le 10\ \mu\text{g/m}^3$ and $PM_{10} \le 20\ \mu\text{g/m}^3$ | 2 |
A05 Part 2 — Enhanced Thresholds for Organic Gases (1 pt)
All seven thresholds must be met in occupiable spaces:
| Compound | Threshold | Compare to A01 |
|---|---|---|
| Acetaldehyde | $\le 140\ \mu\text{g/m}^3$ | not in A01 |
| Acrylonitrile | $\le 5\ \mu\text{g/m}^3$ | not in A01 |
| Benzene | $\le 3\ \mu\text{g/m}^3$ | A01: 10 µg/m³ |
| Caprolactam | $\le 2.2\ \mu\text{g/m}^3$ | not in A01 |
| Formaldehyde | $\le 9\ \mu\text{g/m}^3$ | A01: 50 µg/m³ |
| Naphthalene | $\le 9\ \mu\text{g/m}^3$ | not in A01 |
| Toluene | $\le 300\ \mu\text{g/m}^3$ | A01: 300 µg/m³ — unchanged |
[!TIP] Toluene is the trick. A05 tightens benzene by a factor of about 3 and formaldehyde by a factor of about 5.5, but leaves toluene identical to A01 at 300 µg/m³. An exam item asking "which A05 organic gas threshold matches the A01 precondition?" has exactly one answer.
A05 Part 3 — Enhanced Thresholds for Inorganic Gases (1 pt)
- Carbon monoxide $\le 7\ \text{mg/m}^3$ [6 ppm] (A01: 10 mg/m³ [9 ppm])
- Nitrogen dioxide $\le 40\ \mu\text{g/m}^3$ [21 ppb] — $NO_2$ enters the standard here, not in A01
WELL Core guidance for all three parts: meet the requirements in the whole building; achievement requires access to at least 10% of leased space for testing, as identified by the project.
Feature A13: Enhanced Supply Air — Optimization (1 pt / WELL Core 2 pt)
A13's intent is to mitigate risks from indoor contamination and pollution sources, including infectious disease particles and VOCs. Its logic is explicit: the simplest way to avoid recirculating contaminated air is not to recirculate it; failing that, treat what you recirculate.
A13 Part 1 — Improve Supply Air
Option 1: Air supply requirements. All occupiable spaces use one of:
- (a) 100% outdoor air — supply air has not been recirculated from within the building.
- (b) Partially recirculated air treated with:
- an activated carbon filter; and
- at least one of — (i) a media filter with $PM_{2.5}$ removal $\ge 90%$ (e.g., MERV 14 or F8), (ii) UVGI within the ducts to treat moving air, or (iii) upper-room UVGI.
- (c) Partially recirculated air plus in-space air purification/cleaning devices (quantity appropriate to room volume or area per manufacturer specification) that include an activated carbon filter and either a MERV 14 media filter or UVGI.
Option 2: Filter maintenance. Where filters or other air treatment are used, evidence of replacement or maintenance per manufacturer recommendation is submitted annually through the WELL digital platform.
WELL Core guidance: whole building; up to 10% of tenant-occupied area may be excluded.
Why each medium is specified
- Activated carbon removes VOCs and ozone by physical adsorption across an enormous internal surface area — particle filters cannot capture molecular-scale gases at all, which is why A13 requires carbon in addition to a particle or UV strategy.
- HEPA or near-HEPA media (MERV 14 upward) helps remove virus-laden particles, because viruses usually travel as part of a larger particle.
- UVGI works both in ducts and irradiating the upper room, provided it is powerful enough, or the air speed slow enough, to deliver a sufficient UV dose — WELL states the dose principle rather than a numeric irradiance.
- In-room purifiers put clean air directly in the breathing zone but have low clean-air output, so WELL frames them as best suited to smaller rooms.
[!WARNING] WELL v2 nowhere specifies a 254 nm wavelength, a 4 µW/cm² irradiance, or fail-safe access-door interlocks as UVGI requirements. Those are engineering-handbook and occupational-safety practices — real and important in design, but not WELL compliance criteria. On the exam, UVGI requirements are: in ducts or upper-room (A13), or irradiating coils and drain pans (A14), plus annual maintenance evidence.
Feature A14: Microbe and Mold Control — Optimization (1 pt / WELL Core 2 pt)
Cooling coils condense moisture continuously and are, in WELL's words, "the perfect breeding grounds for mold." Mold on coils sheds particles into indoor air, triggering asthma, headaches, allergies and other respiratory disorders, and has been associated with hypersensitivity pneumonitis, allergic rhinitis, bronchitis and eczema.
A14 Part 1 — Implement Ultraviolet Air Treatment
Option 1: UV system design — both:
- (a) All central air handling units use ultraviolet lamps to irradiate the surfaces of the cooling coils and drain pans.
- (b) All cooling coils and drain pans associated with fan coil units either (1) are irradiated by ultraviolet lamps, or (2) may be opened for inspection for mold growth and cleaned if necessary.
Option 2: UV system maintenance and inspection — both:
- (a) Evidence that ultraviolet lamps were replaced or maintained per manufacturer recommendation, submitted annually.
- (b) All cooling coils without ultraviolet lamps are inspected quarterly for mold growth and cleaned; if necessary, dated photos demonstrating adherence are submitted annually.
WELL Core guidance: whole building; up to 10% of tenant-occupied area may be excluded.
[!TIP] A14 Option 1(b) is unusually forgiving: a project with fan coil units can comply without any UV lamps on them at all, provided those coils and pans can be opened, inspected and cleaned. Pair that with Option 2(b)'s quarterly inspection and you have a maintenance-led compliance route.
The Biology Behind A14 and W07
Understanding why moisture control sits at the centre of both the Air and Water concepts makes the thresholds memorable.
+-----------------------------------------------------------------------------+
| THE INDOOR MOLD COLONIZATION TRIAD |
| |
| [Fungal Spores] + [Cellulose Substrate] |
| \ / |
| \ / |
| v |
| + [Available Moisture] |
| | |
| v |
| ACTIVE HYPHAL GROWTH & GERMINATION |
| | |
| +----------------------+----------------------+ |
| v v |
| [Mycotoxins & Beta-Glucans] [Microbial VOCs (mVOCs)] |
| - Severe asthma exacerbation - Musty, moldy odors |
| - Chronic sinus inflammation - Neurosensory headaches |
+-----------------------------------------------------------------------------+
Dormant spores cannot proliferate without three conditions simultaneously: a viable inoculum (Stachybotrys chartarum, Aspergillus, Penicillium, Cladosporium), a nutritional substrate (cellulose paper facing on drywall, organic adhesives, carpet fibres, settled organic dust) and available moisture. Break any leg and colonization stops — which is why WELL attacks moisture in three separate places: A14 (mechanical system), W07 Moisture Management (building assemblies and operations) and T07 Humidity Control (relative humidity between 30% and 60%).
When mold does germinate it releases mycotoxins (trichothecenes, aflatoxins — cytotoxic and immunosuppressive), β-glucans (fungal cell-wall components that drive non-allergic pulmonary inflammation) and mVOCs (1-octen-3-ol, geosmin — the characteristic musty odour).
Condensation physics
Water condenses wherever humid air meets a surface at or below the dew point temperature. The two prime indoor sites are exactly the ones WELL targets:
- Cooling coils and condensate drain pans, chilled to roughly $45^{\circ}\text{F}$–$55^{\circ}\text{F}$ ($7^{\circ}\text{C}$–$13^{\circ}\text{C}$) — hence A14.
- Thermal bridges — uninsulated steel studs, slab edges and window mullions conducting exterior temperatures inward — hence W07's envelope focus.
A project achieves indoor PM2.5 of 9 µg/m³ and PM10 of 18 µg/m³. How many points does it earn under Feature A05 Part 1?
Which organic gas threshold is identical in Feature A05 Part 2 and Precondition A01 Part 2 Option 1?
A project recirculates a portion of its supply air rather than using 100% outdoor air. What treatment satisfies Feature A13 Part 1 Option 1(b)?
A project has central air handling units with UV lamps irradiating their cooling coils and drain pans, plus twelve fan coil units with no UV lamps. Can it still achieve Feature A14?