NM HVAC Contractor cheat sheet

Construction Industries Licensing Act is compiled at NMSA 1978 Chapter 60, Article 13; rules at NMAC Title 14, Chapter 6.

CID issues journeyman, specialty, and general contractor classifications; HVAC work generally requires MM (mechanical) or a plumbing/mechanical specialty license with a qualifying party.

A qualifying party must pass the trade exam and remain actively in charge; loss of the qualifying party requires notice to CID and replacement within the period set by rule.

Contractors must display license number on advertising, bids, and contracts, and must not bid or contract work above the scope of the classification held.

License renewal is annual with continuing education requirements set by CID rule; expired licenses cannot contract or pull permits.

CID may investigate complaints, issue citations, and impose civil penalties up to the statutory cap per violation; unlicensed contracting is a misdemeanor.

Bond and insurance: contractors must maintain the surety bond and general liability coverage amounts stated in NMAC 14.6.4 for their classification.

Permits must be obtained from the local jurisdiction or CID where no local program exists; final inspection and certificate of occupancy precede legal occupancy.

Gross profit = revenue - direct job costs; net profit = gross profit - overhead. Overhead must be recovered in every hour billed.

Break-even revenue = fixed overhead / gross margin percentage.

Labor burden (payroll taxes, workers' comp, insurance, benefits) is typically added to base wage to compute true hourly cost.

Working capital = current assets - current liabilities; HVAC contractors need enough to fund payroll and material before progress payments arrive.

Retainage commonly 5-10% held until final acceptance; track it as accounts receivable, not cash.

Change orders must be written, priced, and signed before work proceeds to be enforceable.

New Mexico gross receipts tax is imposed on the seller of services; contractors pay it on receipts and should not confuse it with a sales tax.

Job cost codes by phase (labor, material, equipment, subcontract) allow comparison of estimated vs. actual cost to close the feedback loop.

Takeoff quantities come from drawings and specs; pricing = quantity x unit cost + waste factor + markup.

Waste factors: sheet metal roughly 10-15%, pipe and fittings 5-10%, duct insulation 10%.

Bid documents: invitation, instructions to bidders, drawings, specifications, addenda, and the bid form; addenda must be acknowledged.

Bond types: bid bond guarantees the bid; performance bond guarantees completion; payment bond protects subcontractors and suppliers.

Critical path schedule: float is the time an activity can slip without delaying project completion.

Submittals (shop drawings, product data) must be approved before fabrication; resubmittal cycles consume float.

Punch list and substantial completion trigger warranty start, retainage release, and owner occupancy.

Liquidated damages are a pre-agreed per-day amount for late completion; check contract clauses before bidding.

OSHA 29 CFR 1926 covers construction; 1910 covers general industry. Fall protection is required at 6 ft in construction.

New Mexico Occupational Health and Safety Bureau enforces a state plan approved by federal OSHA in lieu of direct federal enforcement.

Ladder rule: 4:1 slope for extension ladders, 3 ft extension above landing, secured at top; never stand on the top two rungs.

Scaffold: guardrails at 42 in plus midrail, fully planked, inspected before each shift by a competent person.

Confined space entry requires permit, atmospheric testing (O2 19.5-23.5%), attendant, and rescue plan.

Refrigerant and nitrogen cylinders must be secured upright; oxygen and acetylene stored 20 ft apart or in a fire-rated cabinet.

Hazard communication: SDS must be accessible for every chemical on site, and containers must be labeled.

Lockout/tagout applies to HVAC servicing of disconnects, motors, and controls; verify zero energy before work.

Manual J calculates room-by-room heating and cooling loads from envelope, orientation, infiltration, and internal gains.

Manual S selects equipment using manufacturer expanded performance data matched to the Manual J load, not nominal capacity.

Manual D sizes ducts for available static pressure and room airflow; total external static pressure determines fan operating point.

Sensible heat equation: Qs = 1.08 x CFM x ΔT (dry air, sea level).

Total heat equation: Qt = 4.5 x CFM x Δh, where Δh is enthalpy difference in Btu/lb.

Latent heat: Ql = 0.68 x CFM x ΔW (grains/lb); total = sensible + latent.

Altitude correction: at 5,000 ft, use about 0.83 instead of 1.08 for the sensible factor because air density is lower.

Design conditions: use ASHRAE 1% cooling and 99% heating design temperatures for the specific New Mexico location, not generic values.

Category I furnace: non-positive vent pressure, vent gas temp above dew point; vents in Type B double-wall vent.

Category IV furnace: positive vent pressure, condensing; uses PVC/CPVC or approved plastic vent and produces acidic condensate.

Combustion air: two permanent openings, one within 12 in of top and one within 12 in of bottom; each sized per the applicable code table.

Natural draft appliances need a properly sized vent with vertical rise; check the National Fuel Gas Code venting tables for capacity and connector rise.

Annual fuel utilization efficiency (AFUE) rates furnaces; 90%+ condensing units require condensate drain with trap.

Boiler safety: relief valve, low-water cutoff, and expansion tank are required; boiler room needs combustion air and relief piping to a safe discharge.

Gas piping sizing uses longest-run method with appliance load in CFH and specific gravity correction; test at 1.5x working pressure for 10 minutes.

Draft hood or draft proving switch confirms adequate flue draft; spillage at a draft hood indicates venting failure.

Vapor compression cycle: compression, condensation, expansion, evaporation; superheat measured at evaporator outlet, subcooling at condenser outlet.

TXV charge is set by superheat; fixed orifice by superheat; subcooling method used for TXV systems.

EPA Section 608: refrigerant may not be knowingly vented; recovery required before opening a system.

Technician certification types: Type I (small appliances), Type II (high-pressure), Type III (low-pressure), Universal (all).

Recovery cylinder must be DOT-approved, not filled over 80% capacity, and labeled with refrigerant type and amount.

Leak repair requirements apply to appliances above 5 lb charge; repair within 30 days and verify with follow-up test, with extended timelines for initial verification.

R-410A operates at roughly 50-70% higher pressure than R-22; use only approved gauges, hoses, and recovery equipment.

Refrigerant blends must be charged as liquid to avoid fractionation; record the type and amount on the appliance label.

Duct sizing by equal friction, static regain, or velocity method; Manual D uses available static pressure and equivalent length.

Friction rate = available static pressure / total effective length; typical residential design is 0.1 in w.c. per 100 ft.

Equivalent length converts fittings to straight duct length; add it to measured length for total effective length.

Return air must be sized for the same airflow as supply; undersized returns raise external static and reduce capacity.

Fan laws: CFM varies with RPM, static pressure with RPM squared, horsepower with RPM cubed.

Outdoor air ventilation per ASHRAE 62.2 for residential; mechanical exhaust required in kitchens and baths.

Duct leakage testing: total leakage limit in IECC is typically 4 CFM per 100 sq ft of conditioned floor area for rough-in tests; verify local code.

Filter selection by MERV; higher MERV increases static pressure drop and must be accounted for in blower selection.

Ohm's law: V = I x R; power: P = V x I for resistive loads; three-phase power = 1.732 x V x I x PF.

Motor full-load amps from NEC Table 430.248 (single-phase) and 430.250 (three-phase); branch circuit conductor sized at 125% of FLA.

Motor overload protection sized per NEC 430.32; short-circuit protection per 430.52.

Disconnect must be within sight of and within 50 ft of the motor; HVAC equipment requires a disconnecting means.

Control circuits commonly 24 VAC; thermostat wire color convention R (power), W (heat), Y (cool), G (fan), C (common).

Two-stage and variable-speed equipment require proper control wiring and configuration; mismatched thermostat causes staging faults.

Grounding and bonding: equipment grounding conductor required; conduit can serve as ground only where permitted by code.

Capacitors: start capacitors briefly boost torque; run capacitors stay in circuit; verify microfarad rating before replacement.

Copper tubing types: K (heavy, underground), L (standard), M (thin wall, above ground); refrigerant lines use ACR copper.

Brazing requires nitrogen purge to prevent internal oxidation; use 15% silver phos-copper for copper-to-copper joints.

Refrigerant line sizing per manufacturer; equivalent length includes fittings; oil return requires minimum velocity and proper traps.

Sheet metal gauges: 26-30 ga typical for residential duct; gauge decreases as duct size increases per SMACNA tables.

Duct sealant and mastic required at all joints; code requires sealing of all transverse joints, seams, and connections.

Pipe insulation and duct insulation R-values are set by the energy code and must be continuous at fittings and hangers.

Support spacing: copper pipe typically every 6 ft for horizontal runs; plastic pipe per manufacturer and code.

Flex duct must be fully extended, supported every 4-5 ft, and limited in length and number of bends to control pressure drop.

New Mexico Energy Conservation Code adopts IECC with state amendments; commercial projects may use ASHRAE 90.1 as an alternative compliance path.

Permits required before installation; inspections typically include rough-in, insulation, and final.

Rough-in inspection verifies framing, duct, piping, and electrical before concealment; schedule before drywall.

Energy code requires duct sealing, insulation R-values, fenestration U-factor, and equipment efficiency minimums (SEER2, HSPF2, AFUE).

New Mexico adopts updated mechanical code (IMC or UMC) by rule; check the edition currently enforced in the jurisdiction.

Certificate of occupancy requires final inspection sign-off; occupancy without it is a violation.

Contractor must post permit and inspection records on site and make them available to the inspector.

Stop-work orders may be issued for work without a permit or code violations; work must be corrected and re-inspected before proceeding.