35.1 Ventilation, Filtration, Humidity, UV & Air Cleaners
Key Takeaways
- Trade Area I (Indoor Air Quality) is 3 percent of the Class A trade exam and 4 percent of Class B. Both classes manage outdoor air, filter types, humidity systems, UV-C coil lamps, electronic air cleaners, and the airflow that makes those devices work; Class B still stops at 25 tons of cooling and 500,000 Btu of heating in any one system.
- ASHRAE 62.1 and FBC Mechanical 2023 Chapter 4 size outdoor air from people plus floor area — more occupants and more square feet need more outdoor air. Florida OA is a latent load; capping the OA damper to hide humidity is not ventilation.
- FBC Mechanical 605.1 filters all return, outdoor, and makeup air upstream of any coil. MERV (ASHRAE 52.2) is particle-capture efficiency: higher MERV means more pressure drop. A 1-inch MERV 13 that needs about 0.30 in. w.g. clean will not fit a 0.50 in. w.g. TESP furnace.
- UV-C coil lamps irradiate the wet coil and drain pan. Never look at an operating lamp (photokeratitis and skin erythema). Use a door interlock. Coil UV does not replace a filter or outdoor air.
- Electronic air cleaners (Trade D item 67 overlap, listed UL 867) ionize particles and collect them on plates. They need a prefilter, a door interlock, and clean plates. They do not remove water vapor, CO2, or VOCs, and they do not waive FBC 605.
35.1 Ventilation, Filtration, Humidity, UV & Air Cleaners
Trade Area I — Indoor Air Quality — is 3 percent of the Class A trade exam and 4 percent of Class B. Class B actually spends a slightly larger slice of its 80-question trade paper on IAQ than Class A spends of 130. The official cluster is one sentence: manage indoor air quality using UV bulbs, filter types, humidity control systems, air cleaners, air flows (test and balance), and the effects of poor air quality on humans. This section is the hardware and the outdoor-air strategy. Section 35.2 is contaminants, source control, TAB of that outdoor air, and what you may honestly say about occupant effects. The 2026 CBT books that carry the cluster are Florida Building Code — Mechanical, 2023 (Chapters 4 and 6, plus 307 for the drain that is a moisture source), Florida Building Code — Energy Conservation, 2023, Refrigeration & Air Conditioning Technology, 9th Edition (2021), Energy Efficient Building Construction in Florida (2024), SMACNA Energy Systems Analysis and Management, 2nd Edition (2014), and NFPA 90A (2015) / 90B (2024) for what may sit in the airstream. Class B still stops at 25 tons of cooling and 500,000 Btu of heating in any one system (F.S. 489.105(3)(g)). A 4-ton house and a 20-ton strip-center rooftop are both Class B IAQ problems. A 40-ton dedicated outdoor-air unit is Class A to contract; the ventilation-rate idea and the UV safety rule do not change.
Quick Answer: Dilute with outdoor air sized from people + floor area (ASHRAE 62.1 / FBC Chapter 4). Filter upstream of the coil (605.1); MERV up means ΔP up. Dehumidify Florida outdoor air — latent load, not a 75°F dry-bulb trophy. UV-C coil lights need a door interlock; never look at the lamp. Electronic air cleaners ionize and collect; they do not replace a listed filter.
Why Trade I is not a filter catalog
Pearson VUE will hand you a MERV upgrade that starves the coil, a UV lamp someone is staring at, an electronic air cleaner with the interlock jumped, a humidistat that never runs because the unit is oversized, or an outdoor-air damper pinned shut “to save energy.” Trade D already hung the filter rack (Section 24.3) and the EAC power pack (Section 27.4). Trade I asks whether that hardware actually manages indoor air in a warm-humid Florida building (Energy Conservation Climate Zones 1A and 2A). Clogged drains, musty attics, and 80 percent indoor RH at 74°F are the same hours this 3–4 percent is testing.
Ventilation: dilution with outdoor air (qualitative 62.1)
Ventilation here means outdoor air (OA) brought in to dilute indoor-generated contaminants and to replace air that exhaust took out. It is not the same word as “the supply fan is running.” Recirculated room air that never saw the outdoors can keep dry-bulb happy and still fail FBC Chapter 4.
ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, is the commercial method FBC Mechanical Table 403.3.1.1 implements. Qualitatively, the ventilation rate procedure adds two pieces: a people outdoor-air rate times the zone population, plus an area outdoor-air rate times the floor area. More occupants and more square feet need more outdoor air. A densely occupied classroom needs more OA per square foot than a lightly occupied storage room of the same area. You look up the row in the open-book table; you do not invent a 15-cfm-per-person rule of thumb and call it code. Residential whole-house ventilation (ASHRAE 62.2 language in the energy and green-building books) is the dwelling cousin: a continuous or intermittent outdoor-air path, not a bath fan that runs when someone remembers.
FBC Mechanical 401.2 requires ventilation by natural means (402) or mechanical means (403). Florida production housing and almost every commercial occupancy on this exam are mechanical. 401.4 keeps the outdoor-air intake away from the thing you would otherwise suck back in: not less than 10 feet horizontally from hazardous or noxious sources — plumbing vents, chimneys, exhausts, streets, alleys, parking lots, and loading docks — with the code’s 3-foot-below rule when a source sits close, and the 25-foot vertical exception when an intake has to sit nearer a street or parking deck. An intake in a loading-dock well, next to a grease exhaust, or in an attached-garage soffit is not ventilation. It is a contaminant inlet.
Florida’s outdoor air in cooling season is hot and wet. Every extra cfm of OA is latent load (Chapter 16.2 sensible versus latent; Chapter 17.1 coil SHR). Approximate grains: outdoor 95°F dry-bulb / 75°F wet-bulb sits near 110 grains; a 75°F room at 50 percent RH sits near 65 grains. Latent from that air is (Q_l = 0.68 \times \text{CFM} \times \Delta\text{grains}). At 500 cfm OA, (0.68 \times 500 \times 45 \approx 15{,}300) Btu/h of moisture load — more than a ton of latent — before people and wet infiltration. Dumping unconditioned OA, or oversizing so the DX coil short-cycles above dew point, is how you get cold, clammy rooms. Demand-controlled ventilation that uses CO2 as an occupancy proxy can cut OA toward a code floor when the room is empty; it must not close the OA damper to zero while people are in the space (Section 35.2). An energy recovery ventilator (ERV) can transfer moisture as well as heat and take some of that latent off the DX coil. An HRV is sensible-only. Neither device waives the outdoor-air quantity.
Filtration: MERV is capture, pressure drop is the tax
FBC Mechanical 605.1: approved filters; all return, outdoor, and makeup air filtered upstream of any heat exchanger or coil. 605.2: media listed UL 900 (dwelling-unit exception), HEPA UL 586, electrostatic UL 867. 605.3: air spread evenly over the entire filter. Section 24.3 already used that code as an install. Trade I uses it as IAQ.
Minimum Efficiency Reporting Value (MERV) is ASHRAE 52.2. It is a particle-capture scale, not a medical rating and not a water-vapor rating.
| Filter / cleaner | IAQ function | What it is not |
|---|---|---|
| Low-MERV throwaway (about MERV 4–6, 1-inch) | Lint and large dust; protects the coil from debris | Fine-particle IAQ; a clean coil is not clean room air |
| Pleated media (about MERV 8–11) | Pollen, dust-mite debris, many larger mold spores | A license to ignore outdoor air or a clogged drain |
| Higher-MERV media (about MERV 13 in a deep cabinet) | Finer particles if the fan still delivers design CFM | A 1-inch MERV 13 stuffed into a 0.50 in. w.g. furnace |
| HEPA (UL 586) | Very high particle capture in a listed housing whose fan was selected for the drop | A retrofit pad in a residential 1-inch slot |
| Gas-phase (activated carbon) | Odors and some VOCs | Particle MERV; carbon does not replace 605.1 |
| Electronic air cleaner (UL 867) | Charges particles and collects them on plates | A substitute for a listed prefilter, outdoor air, or source control |
Higher MERV always costs pressure drop, and Florida return air is humid, so loaded media climbs faster than a dry-climate catalog curve. A 1-inch MERV 13 that needs on the order of 0.3 in. w.g. clean does not fit a furnace selected at 0.50 in. w.g. total external static after you pay the wet coil (~0.25–0.30) and the attic flex. The IAQ result of that “upgrade” is low CFM, a coil that ices, poor dehumidification, and occupant complaints — the opposite of Trade I. Put the same MERV 13 in a 4- or 5-inch media cabinet at lower face velocity (keep throwaway face velocity near 300–350 fpm as a design habit) and the drop can be tolerable. ECM blowers that hold CFM will raise watts until they fault; they do not repeal 605.1 or the nameplate TESP.
Humidity control systems
Florida IAQ is moisture-first. Occupied-space relative humidity that sits above about 60 percent for long periods supports mold growth on cool surfaces (supply drywall, closets, behind furniture). Keep indoor RH from lingering in that band — commonly discussed as 30–50 percent as a comfort target and below 60 percent as a moisture-control ceiling. That is building physics, not a diagnosis of a disease.
The cooling coil is the first dehumidifier: the surface must sit below dew point and the unit must run long enough to condense. An oversized machine that hits 72°F dry-bulb in ten minutes and shuts off leaves the room at 70 percent RH. Sensible oversizing is an IAQ defect in Zones 1A/2A.
Humidity systems the outline expects you to name:
- Humidistat / dehumidistat (Section 27.2): in Florida it makes on humidity rise to call cooling, a dehumidifier, or reheat. Low-voltage HVAC wiring — Class A and Class B. It is not a freeze stat.
- Reheat (hot-gas, wraparound, or electric): overcool to wring moisture, then reheat so the room is not a meat locker. Energy code still governs electric reheat.
- Whole-house / ducted dehumidifier: a dedicated refrigerated coil, often piped into return and supply, with its own condensate (still 307).
- Dedicated outdoor-air system (DOAS): conditions OA to a dry leaving point before it mixes. Common on Class A commercial jobs; Class B still owes the idea on a 20-ton RTU with an OA hood.
- ERV: transfers heat and moisture. An HRV does not dump the latent.
Humidification (steam or evaporative) is the winter / north-Florida exception, not the Jacksonville August default. An evaporative pad in a Florida supply duct is a mold farm.
UV-C coil lights — function and the safety rule you will not miss
Ultraviolet-C (UV-C) lamps used in HVAC are typically low-pressure mercury germicidal lamps with output near 254 nanometers. The Trade I install that actually shows up is a coil-irradiation (and drain-pan) light: the lamp sits in the air handler so the wet coil face and the pan receive UV, reducing microbial growth on those surfaces. That is a maintenance and odor tool for a coil that would otherwise slime. It is not a claim that the occupied building is sterile, and it is not a substitute for a filter (particles) or for outdoor air (gases, CO2, humidity).
In-duct airstream UV, sized for a moving stream, needs a much higher dose (intensity × dwell time) than a lamp hanging in front of a coil. If the exam item is “UV bulbs” on an air-conditioning contractor outline, treat it as coil lights unless the stem clearly says otherwise.
Safety — non-negotiable:
- Never look at an operating UV-C lamp. UV-C causes photokeratitis (a painful “welder’s flash” of the cornea) and skin erythema. There is no “quick glance” exception.
- Access panels need a door interlock that kills the lamp when the door opens, plus a label.
- Viewports, if any, must be UV-blocking.
- True germicidal 254 nm lamps with doped glass are built to be ozone-free. Lamps that pass 185 nm generate ozone, which is itself an IAQ contaminant. Use the listed HVAC lamp.
- Broken lamps contain mercury. Handle per the IOM — do not sweep powder through the blower.
Lock out (Chapter 33) before you change a lamp. The ballast is still inside 489.105 HVAC control / dedicated-circuit work. A new lighting homerun is not.
Electronic air cleaners — IAQ function (Trade D item 67 overlap)
Section 27.4 hung the door interlock and the power pack. Trade I asks what the machine does to the air. An electronic air cleaner (EAC) is an electrostatic precipitator: a high-voltage ionizing section charges particles; collection plates attract them. A prefilter still catches lint so the ionizer does not become a lint furnace. Efficiency is highest when plates are clean; a gray, loaded cell dumps agglomerated dirt back into the airstream and can arc. Wash cells per the IOM; never wash with power applied.
EACs can capture fine particles a cheap throwaway will miss. They do not reliably remove gases, CO2, or water vapor. They do not waive FBC 605. They list to UL 867. Some consumer ionizers without collection plates charge dust so it sticks to walls (black-wall effect) and may emit ozone. If the stem says electronic air cleaner, the exam wants the ionizer + collector + interlock + prefilter machine, installed upstream of the coil, not a plug-in gadget on a nightstand.
Worked static/IAQ example. A Cape Coral 3-ton air handler is selected at 0.50 in. w.g. TESP. Wet coil 0.28, duct 0.16, leftover for the filter 0.06. The owner wants “hospital air.” A 1-inch MERV 13 at 0.30 clean does not fit. Legal paths: a 5-inch MERV 13 media cabinet at about 0.10, or a listed EAC plus a low-ΔP prefilter if the remaining static still closes, plus OA that the coil can dehumidify. Staring into a new UV lamp while you “check if it is on,” pinning the OA damper shut, and stuffing the 1-inch MERV 13 is three Trade I failures in one attic.
Florida HVAC scenario
Gulf Breeze Air, a certified Class B shop, change-outs a 4-ton split in a 2,100-square-foot Climate Zone 2A house. The salesperson sells a 1-inch MERV 13, a UV-C “virus light” with no interlock, and an electronic air cleaner. The helper leaves the OA duct capped “because humidity,” and the UV lamp is tested by looking into the open blower compartment with the door switch taped. Four independent misses: (1) MERV versus ΔP — 1-inch MERV 13 on a 0.50 TESP machine; (2) OA — FBC Chapter 4 / 62.1 dilution is not optional because the day is humid; you dehumidify the OA; (3) UV-C — never look at the lamp, and tape on the interlock is a safety fail; (4) the EAC is legal IAQ hardware only with the door interlock, prefilter, and a remaining static budget — it does not replace OA or a drain that still has to meet 307. Class B is legal at 4 tons. The license card does not rewrite 605, 401.4, or UV safety.
Traps: (1) Treating MERV as a medical rating or a humidity remover. (2) Capping OA to “solve” humidity. (3) Looking at UV-C. (4) Calling an ionizer without plates an EAC. (5) Using an evaporative humidifier as Florida dehumidification.
A Class B contractor on a 4-ton Florida change-out wants to cap the outdoor-air duct because the house feels clammy. Which statement is the correct Trade I response?
Which UV-C practice is required when coil-irradiation lamps are used on a Florida air handler?
A furnace selected at 0.50 in. w.g. total external static has 0.06 in. w.g. remaining for the filter after the wet coil and duct. The owner wants better particle capture. Which approach matches Trade I and FBC Mechanical 605?