17.3 Selecting Equipment, Location & Codes

17.3 Selecting Equipment, Location & Codes

Trade Area A also asks you to determine the proper HVAC equipment: manufacturer data, sizing, loads, psychrometrics, locations, and codes. Selection is not a catalog photo. It is a license-scope check, a Manual S / expanded-data check, a psychrometric latent check, and a Florida Building Code — Mechanical, 2023 check of where the box may sit and how a technician will service it.

Quick Answer: Pick listed, AHRI-matched equipment from expanded performance data at the design wet-bulb and dry-bulb, inside Class B's 25-ton / 500,000 Btu per-system cap (Class A unlimited). Then place it where FBC Mechanical 2023 allows access, condensate overflow protection, and manufacturer clearances — attic air handlers need the 30 × 22 inch, 20-foot passageway rules in Section 306.3.

Manufacturer data, loads, and psychrometrics

FBC Mechanical Section 312 points design loads to ASHRAE/ACCA Standard 183 (or an approved Energy Conservation Chapter 3 method). FBC Energy R403.7.1 points residential heating and cooling to ACCA Manual S based on Manual J, with no designer safety factors and no future-expansion padding. Cooling total capacity must be at least the calculated total load and not more than 1.15 times that load, or the closest available size. Latent capacity shall not be less than the calculated latent load. AHRI nominal total capacity is not the selection number (R403.7.1.1). Heat pumps size on cooling, and the 1.15 cooling cap still holds even if heating load is larger (R403.7.1.2.1). Climate Zone 2 (almost all of Florida) does not allow electric resistance as the primary heating system (R403.7.2).

Read the expanded performance table at the outdoor design dry-bulb (Florida summer often 91–95°F depending on the county column) and the indoor entering WB/DB. Confirm the blower CFM from Section 17.1 is a published operating point at a static the duct (Section 17.2) can hit. Confirm SEER2/EER2/HSPF2 on the AHRI-matched combination meets the federal floor for the installation location — 14.3 SEER2 for a typical split air conditioner under 45,000 Btu/h in DOE's Southeast region. The unit must still be listed and labeled and installed in accordance with the listing (FBC Mechanical 304.1). Those manufacturer pages are code for side and top clearances and for outdoor-unit airflow. A 12-inch side clearance when the listing says 24 inches is a failed inspection, not a field efficiency trick.

Class A versus Class B is a selection filter

Class A (F.S. 489.105(3)(f)) is unlimited in capacity and may include boilers, unfired pressure vessels, and pneumatic control piping. Class B (F.S. 489.105(3)(g)) is limited to 25 tons of cooling and 500,000 Btu of heating in any one system and does not pick up those boiler, vessel, or pneumatic items. One packaged rooftop at 30 tons (360,000 Btu/h) is Class A work. Two independent 15-ton systems, each with its own distribution, can be Class B. Two compressors in one 30-ton cabinet are still one system. A 20-ton rooftop with a 600,000 Btu gas heat module is still out of Class B even though cooling tons look legal. Class B candidates still answer theory questions about large plants; the Class B outline drops 25–100 ton, over-100 ton, and centrifugal installs.

Recommending, bidding, or negotiating work beyond the cap is still contracting (F.S. 489.105(6)). Select a legal machine, split the building into independent systems that truly are independent, hire Class A, or walk away.

FBC Mechanical 2023 — location and access

Section 303 keeps fuel-fired appliances out of prohibited rooms (sleeping rooms, bathrooms, and similar locations, with the code's listed exceptions) and addresses outdoor listings and pits. Chapter 3 flood provisions (IMC-based 301.16) require mechanical equipment in flood hazard areas to sit at or above the elevation required by the Florida Building Code, Building — coastal and riverine jobs fail when the air handler sits on a slab below design flood elevation. Section 304.3 elevates ignition sources of fuel-fired appliances at least 18 inches above the floor in garages and other hazardous locations. Section 304.11 Guards: where components that require service sit within 10 feet of a roof edge more than 30 inches above the surface below, provide 42-inch guards (or equivalent fall protection the code accepts).

Section 306 Access and service space is the attic-AHU paragraph the exam likes.

• 306.1 Working space in front of equipment that needs service: a level space not less than 30 inches deep and 30 inches wide.
• 306.2 Rooms containing appliances: a door and an unobstructed passageway not less than 24 inches wide, large enough to remove the largest appliance.
• 306.3 Appliances in attics. Opening and unobstructed passageway large enough to remove the largest appliance. Passageway not less than 30 inches high and 22 inches wide, not more than 20 feet in length measured along the centerline from the opening to the appliance, with continuous solid flooring not less than 24 inches wide. A level service space not less than 30 inches deep and 30 inches wide at the front or service side. Clear access opening minimum 20 inches by 30 inches, and large enough to remove the largest appliance.
• 306.3.1 Electrical. A luminaire controlled by a switch at the passageway opening, and a receptacle at or near the appliance, in accordance with NFPA 70.
• 306.4 Under-floor appliances use a similar 30 × 22 passageway idea with a 20-foot limit.
• 306.5 Equipment on a roof or elevated structure more than 16 feet above grade needs a permanent interior or exterior means of access — not a leaning ladder from the pickup.

Outdoor units need manufacturer airflow clearances, a level pad or approved rack, Florida wind anchorage, and flood elevation. Do not install a condenser in a decorative well that recirculates hot discharge air — that is the P-h / efficiency failure from Section 17.1. Return air is not taken from a garage, bathroom, kitchen, or hazardous space (Mechanical Chapter 6). Outdoor air intakes stay the Chapter 4 distance from plumbing vents, exhausts, and lot lines.

Condensate overflow — attic coils destroy ceilings

Section 307 Condensate disposal. Cooling coils drain to an approved place of disposal. F.S. 489.105 lets the air-conditioning contractor run condensate to an existing safe waste, not a new sanitary tap. Drain pipe is not smaller than the pan outlet and not smaller than 3/4 inch. Where overflow would damage building components — every Florida attic air handler, every closet above finished space — auxiliary/secondary protection is required: an auxiliary drain pan with a drained secondary line to a conspicuous point, a secondary drain from the pan, an auxiliary pan with a water-level detection device that shuts the equipment off, or a water-level detection device (float switch) on the primary pan that shuts the equipment off, as the section allows. A primary 3/4-inch PVC to the exterior with no overflow plan is not a complete attic design. Trap the drain as required, support it, and do not dump the secondary back into the primary pan or into a sanitary sewer stub.

FBC Energy R403.3.6 and related envelope rules still constrain when an air handler may live in an unconditioned attic on a prescriptive-path house; even when the attic location is allowed, 306.3 and 307 do not go away. An attic unit that cannot come out through a 20×30 opening is a selection error, not a “we will tilt it” field note.

Putting location, capacity, and codes on one decision

Selection sequence the exam expects:

1. License. Class B 25 tons / 500,000 Btu per system; Class A unlimited; no boilers or pneumatics on Class B.
2. Load. Manual J or Standard 183; indoor 75°F and the county's outdoor design; latent and sensible separate.
3. Psychrometrics. Coil leaving DB/WB and SHR that meet latent; CFM = Btu/h ÷ (1.08 × ΔT) for sensible.
4. Manufacturer. Expanded data, AHRI match, SEER2 floor, MCA/MOCP, physical size through the 20×30 attic opening.
5. Location. Listing clearances, 306 access, 307 condensate, flood, wind, intake/exhaust separation, 306.5 roof access, 304.11 guards.
6. Duct. Ductulator + SMACNA pressure class + R-8 attic insulation so the selected CFM is real.

Changing location after permit (air handler from garage to attic, condenser into a courtyard well) is a code modification, not a Saturday change-order. Recommend it with an RFI and a revised Manual S, not with a sawzall.

Florida HVAC scenario

A certified Class B firm in Pinellas County is asked to replace a failed air handler in a 1960s ranch. The attic hatch is 18 × 22 inches. The walkway is OSB scraps that stop 8 feet short of the unit. There is a primary condensate line and nothing else. The owner “already bought” a 4-ton air handler because the outdoor unit says 4 tons; Manual J total is 29,000 Btu/h (the 4-ton expanded total is about 47,000 Btu/h, 1.62 times the load). Three code and selection failures, in the order you write them on the exam: (1) R403.7.1.1 — do not install the 4-ton; select expanded-data capacity inside 1.15 (33,350 Btu/h) with latent at least the calculated latent; (2) 306.3 — the opening is smaller than 20 × 30, there is no 24-inch continuous flooring, no 30×30 service space, and no 306.3.1 light/receptacle; (3) 307 — add secondary/auxiliary overflow protection before the coil sits over a living-room ceiling. Class B is fine on tonnage if the replacement is about 2.5 tons. The 4-ton carton in the driveway is not a code document. If the same owner had pointed at a 30-ton rooftop on the medical office next door, Class B would have been the first “no,” before any attic hatch was measured.

Traps: (1) “Closest size” as an excuse to jump a full ton when a matching size exists. (2) Treating manufacturer clearance as optional. (3) A 24-inch-wide attic aisle that is 22 feet long (fails the 20-foot cap). (4) Secondary drain dumped back into the primary pan. (5) Class B bidding a 30-ton rooftop because a crane can set it.