West Virginia HVAC Contractor

Key Concepts

IMC definitions (Chapter 2). A low-heat appliance (residential appliance) is one in which the products of combustion at the point of entrance to the flue under normal operating conditions have a temperature of 1,000°F (538°C) or less (§202). Terms not defined in the IMC but defined in the IBC, IFC, IFGC or IPC take the meanings in those codes (§201.3); terms not defined by those methods "shall have ordinarily accepted meanings such as the context implies" (§201.4).

IMC general installation. - Space-heating systems must maintain not less than 68°F (20°C) at a point 3 feet above the floor on the design heating day (§309.1). - Appliances in private garages and carports: minimum clearance 6 feet above the floor (§304.7); ignition sources in hazardous locations and garages elevated not less than 18 inches above the floor surface (§304.3). - Wood studs in exterior walls and bearing partitions: not cut or notched in excess of 25 percent of depth (§302.3.2). Notches on the ends of joists: not to exceed one-fourth the joist depth (§302.3.1).…

Key Concepts

• Output of a load estimate. A combined heating/cooling estimate produces five values: sensible cooling load (Btuh), latent cooling load (Btuh), cooling airflow, sensible heating load (Btuh), and heating airflow. Latent load is a cooling-only consideration and is not a factor in heating equipment selection (Section 1.1.0, Page 1).
• ACCA manuals. Manual J = residential load calculation; Manual N, Commercial Load Calculation = commercial structures; Manual D = duct design; Manual S = residential equipment selection (Sections 1.0.0 and 1.2.0, Pages 1 and 7).
• Outdoor design conditions. Use the Heating 99% Dry Bulb and Cooling 1% Dry Bulb columns; record extremes are isolated and short, and would exaggerate the load (Section 2.0.0, Figure 6, Pages 8–9). A supplemental micro-climate table covers areas of Arizona, California, Hawaii, and Nevada (Page 8).
• Heat transfer terms. Conductivity = heat flow through one inch of a homogeneous material; conductance = heat flow rate (Btuh) through one square foot of a nonhomogeneous material of a certain thickness at 1°F difference between its two surfaces…

Key Concepts

Dryer exhaust (IMC Chapter 5) - Protective shield plates shall be placed on the finished face of all framing members where there is less than 1-1/4 inches (32 mm) between the duct and the finished face of the framing member — Section 504.7. - Maximum exhaust duct length is 35 feet from the transition duct connection to the outlet terminal, reduced by the equivalent lengths in Table 504.8.4.1 — Section 504.8.4.1. - Screens shall not be installed at the duct termination of dryer exhaust ducts — Section 504.4. - Fire dampers, combination fire/smoke dampers and any similar devices that will obstruct the exhaust flow shall be prohibited in clothes dryer exhaust ducts — Section 504.2. - Dryer exhaust shall be independent of all other systems — Section 501.2.

Key Concepts

Thermostat setting range and sequence. A space-sensing thermostat is wall mounted and capable of being set from 55°F (13°C) to 85°F (29°C), and should operate heating and cooling in sequence without overlap — Residential Comfort System Installation Standards (8th ed.), Section 9.3.1, Page 9.2.

Mounting height. The generally accepted mounting height is 60 in. above finished floor, but where the Americans with Disabilities Act or the Fair Housing Act applies, the height is 48 in. (1.22 m) — RCSIS Section 9.3.4, Pages 9.2–9.3. Verify which rule applies before mounting.

Outdoor thermostats on heat pumps. Outdoor thermostats keep auxiliary heat off until outdoor temperature falls near the balance point. Without an outdoor thermostat or sensor, every manual turn-up of a two-stage thermostat energizes the less-efficient auxiliary heat — RCSIS Section 9.3.3, Page 9.2. When adding a setback thermostat to an existing air-source heat pump, verify an outdoor thermostat is installed to control auxiliary heat and is properly set; otherwise potential savings are "more than lost" and energy use may increase — *RCSIS Section…

Key Concepts

Duct sizing and classification - Ducts within a single dwelling unit: sized per ACCA Manual D, the appliance manufacturer's installation instructions, or other approved methods. Ducts in all other buildings: sized per the ASHRAE Handbook of Fundamentals or equivalent computation procedure (IMC 603.2, p. 72). - Ducts are classified at positive or negative 0.5, 1.0, 2.0, 3.0, 4.0, 6.0 or 10.0 inches of water column; the pressure classification must equal or exceed the design pressure (603.3, p. 72).

Materials and construction - Metallic ducts: built per SMACNA HVAC Duct Construction Standards—Metal and Flexible. Exception: single dwelling units may use Table 603.4 thicknesses — but footnote a requires SMACNA where ductwork exceeds 20 inches by dimension or exceeds 1-inch water gauge (603.4 / Table 603.4, p. 72). - Round metallic ducts: not less than three sheet metal screws or rivets equally spaced around the joint (603.4.1). Crimp joints for round and oval metal ducts: lapped not less than 1 inch, male end extending into the adjoining duct in the direction of airflow (603.4.2,…

Key Concepts

Copper tubing (NCCER Module 03103 / HVAC Basics Ch. 2) - Types are distinguished by wall thickness; OD is the same for a given nominal size. A 1" Type M tube has a 0.035" wall; a 1" Type L tube has a 0.050" wall. Type K is the thickest-walled and heaviest; Type DWV (drain, waste, vent) has thin walls (Sec. 1.1.1). - Types K, L, M and DWV are called out by nominal size; Type ACR is called out by its actual outside diameter. Nominal sizes have an actual OD 1/8" larger than the stated size, so 1" Type L (1.125" OD) is the same tube as 1-1/8" ACR (Secs. 1.1.1, 1.1.3). ACR is identical to Type L in construction and dimensions, and is purged and nitrogen-charged. - Color codes (Table 1): K green, L blue, M red, DWV yellow, ACR blue — ACR shares Type L's color. - Cutting (Sec. 2.1.2): a tubing cutter is always preferred (square end, no saw cuttings). A hacksaw is used only where obstructions prevent the…

Source: HVAC Basics for Contractors, Chapter 1 — Basic Safety (Construction Site Safety Orientation), NCCER Module 00101.

Key Concepts

Hazard recognition and recordkeeping - Per OSHA, an incident is an unplanned event that does not result in personal injury but may result in property damage or is worthy of recording; an accident is an unplanned event that results in personal injury and/or property damage (Ch. 1, Book Page 3 text). - Studies show that for every serious or disabling injury there were 10 injuries of a less serious nature and 30 property damage incidents, and 600 near-miss incidents per serious or disabling injury (Book Page 5). - US employers with more than 10 employees must maintain a log of significant work-related injuries and illnesses on specific OSHA forms, with a summary posted at required intervals (Book Page 16). - TSA vs. JSA: both identify hazards and safeguards before work; the difference is the reporting form — a TSA typically uses a pre-printed, fill-in-the-blank checklist, and some companies require workers to sign it before starting…

Key Concepts

Boilers, water heaters and pressure vessels (IMC Chapter 10) - Scope exclusions: pressure vessels used in refrigeration systems are exempt from Chapter 10 because they are regulated by Chapter 11 (Section 1001.1, Exception 5). Exception 4 exempts unfired pressure vessels of 5 cubic feet or less operating at pressures not exceeding 250 psi in Groups B, F, H, M, R, S and U. - Controls and safety devices: boilers with fuel input 12,500,000 Btu/hr or less → ASME CSD-1; inputs greater than 12,500,000 Btu/hr → NFPA 85 (Section 1004.1). Boilers are designed/certified to the ASME Boiler and Pressure Vessel Code, Section I or IV. - Working clearance: passageways around all sides of boilers shall have an unobstructed width of not less than 18 inches (457 mm), unless otherwise approved (Section 1004.3). - Top clearances are per Table 1004.3.1 (see below). - Combination potable water-heating/space-heating systems needing water higher than 140°F require a temperature-actuated mixing valve conforming to ASSE 1017, tempering the potable hot water distribution to 140°F or less (Section 1002.2.2). -…