What is a Heating Coil in HVAC System?

A heating coil in an HVAC system is a device that transfers heat to air using hot water, steam, or electric resistance, raising the air temperature as it passes through the system.

Explanation:

You’ll typically find heating coils in air handlers or ductwork. When air flows over the coil, thermal energy from the hot water, steam, or electric elements is transferred to the air. Water-based coils (hydronic) use copper or aluminum tubes with fins to maximize heat exchange, operating at 120°F–180°F (49°C–82°C). Steam coils require higher temperatures (212°F+/100°C+) and pressure-resistant materials. Electric coils use resistive wires, reaching 500°F–1000°F (260°C–538°C), but are less efficient and suited for smaller spaces. 

Heating coils are sized by capacity (BTU/hr or kW) and airflow (CFM). For example, a 10 kW electric coil heats ~340 CFM of air by 50°F (28°C). They’re common in commercial systems for precise temperature control, while electric variants are used in heat pumps or supplemental heating. Proper maintenance ensures efficiency and prevents issues like airflow blockage or corrosion.

How Do Heating Coil Works?

A heating coil works by warming air using electricity, hot water, or steam. Here’s how its components function:

Heating Coil Core: Made of conductive metals like copper or aluminum, this coil transfers heat. Electric coils use high-resistance wires (5–20 kW power), while hydronic (water/steam) coils circulate hot water (160–200°F) or steam (2–15 psi pressure).

Heat Source:

Electric: Powered by 240V circuits, generating heat via electrical resistance.

Hydronic: Connected to a boiler, supplying heated water/steam through pipes.

Air Handler: A fan (1,000–5,000 CFM airflow) blows air over the coil, raising its temperature before distributing it.

Thermostat: Monitors room temperature. When it drops below your setpoint, it signals the coil to activate.

Heat Exchanger (Hydronic): Transfers heat from water/steam to the coil without mixing fluids, ensuring efficiency.

Control Valve (Hydronic): Regulates water/steam flow (0.5–2 GPM for water) to maintain precise temperature control.

When you adjust the thermostat, the system triggers the heat source and airflow, warming your space efficiently. Electric coils respond faster (~seconds), while hydronic systems rely on boiler cycles (~minutes).

Where are HVAC Heating Coils are located?

HVAC coils are located both inside and outside forming a continuous loop. Here’s how they’re positioned and what makes them unique:

Evaporator Coil:

Location: Inside your home, mounted in the air handler (often above the furnace) or within ductwork near the plenum (air distribution box).

Role: Absorbs heat from indoor air as refrigerant evaporates, cooling your home. In heat pumps, it switches to releasing heat during winter.

Condenser Coil:

Location: Outside, inside the condenser unit (metal cabinet housing the compressor and fan).

Role: Releases heat from refrigerant to the outdoors during cooling mode. In heat pumps, it reverses to absorb outdoor heat in winter.

Heating Coil (Optional):

Electric: Nestled in the air handler near the evaporator, using high-resistance wires (5–20 kW) for quick heat.

Hydronic: Integrated into ducts or air handlers, linked to a boiler via pipes circulating hot water (160–200°F) or steam (2–15 psi).

System-Specific Variations:

Split Systems: Coils are split evaporator indoors, condenser outdoors.

Packaged Units: All coils (heating/cooling) are in a single outdoor rooftop or slab-mounted unit.

Dual-Function Heat Pumps: Use a reversing valve to swap evaporator/condenser roles seasonally.

Why It Matters:

The evaporator and condenser are linked by refrigerant lines (copper tubing), creating a closed loop.

Dust or ice on coils reduces efficiency clean indoor coils annually and keep outdoor units debris-free.

Access panels (indoor) or removable grilles (outdoor) let technicians service coils without dismantling the system.

Can Your Repair HVAC Coil On your Own?

No, Repairing HVAC coils yourself is not recommended for most issues due to safety risks, technical complexity, and legal requirements. Because coils are part of a sealed refrigerant loop. Repairs require EPA certification (illegal to handle refrigerants without it).  For leaks, electrical faults, or refrigerant issues, hire a licensed HVAC technician. They have tools, training, and certifications to repair coils safely and legally.

How Long Does It Take to Replace HVAC Coil?

A seasoned HVAC technician typically takes 2–3 hours to replace an AC coil in a straightforward case. Here’s the breakdown:

Steps Involved:

Removal/Installation: 30–60 minutes (depends on coil accessibility).

Brazing/Purging: 20–30 minutes (sealing refrigerant lines with nitrogen to prevent oxidation).

Pressure Testing: 15–20 minutes (checking for leaks at 150–300 psi).

Evacuation: 30–45 minutes (vacuuming moisture/air from the system).

Recharging Refrigerant: 15–30 minutes (based on system size, e.g., 3–5 lbs for residential units).

Factors Extending Time:

Complex Systems: Multi-zone units or rooftop installations add 1–2 hours.

Refrigerant Type: R-410A requires precise charging vs. older R-22.

Corrosion/Damage: Stubborn bolts or rusted components delay removal.

Note: DIY replacement is unsafe and illegal (refrigerant handling requires EPA certification). Always hire a licensed pro for compliance and efficiency.

How much does it cost to replace the coil in HVAC System?

The cost to replace HVAC coil in Pakistan ranges from PKR 10,000 to PKR 40,000 for the coil itself, with total expenses (including labor) typically reaching PKR 15,000–60,000. Below is a detailed breakdown:

Key Cost Factors

Type of Coil:

Evaporator Coil (indoor unit): PKR 15,000–40,000 (more complex to access).

Condenser Coil (outdoor unit): PKR 10,000–35,000 (simpler design but prone to weather damage).

System Size:

1–1.5 Ton Systems: PKR 10,000–25,000 (coil only).

2–3 Ton Systems: PKR 25,000–40,000 (coil only).

Brand:

OEM Coils (e.g., Daikin, Haier): 20–40% costlier than generic/local brands.

Aftermarket Coils: Cheaper (PKR 8,000–30,000) but may lack durability.

Labor Costs:

Basic Replacement: PKR 3,000–10,000 (for easily accessible units).

Complex Jobs (e.g., rooftop/ductwork adjustments): PKR 10,000–20,000.

Location:

Urban Areas (Karachi, Lahore): Labor costs 10–20% higher than rural regions.

Additional Considerations

Warranties: Many brands (e.g., Gree, Haier) offer 1–5-year warranties on coils, reducing part costs if covered.

Refrigerant Recharging: Adds PKR 3,000–8,000 (for R-410A or R-32 systems).

Energy Efficiency: Inverter-compatible coils cost 15–25% more but cut long-term power bills.

Example Total Costs

1.5-Ton Split AC (Evaporator Coil):

Coil (PKR 18,000) + Labor (PKR 7,000) + Refrigerant (PKR 5,000) = PKR 30,000.

2-Ton Commercial Unit (Condenser Coil):

OEM Coil (PKR 35,000) + Complex Labor (PKR 15,000) = PKR 50,000.