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Mechanical / HVACaka: cooling coilaka: heating coilaka: DX coil

Coil

In Plain English

A finned tube bundle inside an air handler that heats or cools air as it passes over the surface.

Definition

A heat transfer element in an air handling unit or terminal device consisting of rows of tubes carrying hot water, chilled water, steam, or refrigerant, surrounded by aluminum fins that increase the heat transfer surface area. Heating coils warm supply air; cooling coils cool and dehumidify it. Coil performance is characterized by entering and leaving air conditions and water flow rate.

Why It Matters in Bidding

Coils are priced as part of air handler and terminal unit equipment, and their specified entering/leaving conditions and flow rates drive both equipment cost and the associated piping, valves, and controls in the mechanical bid. Estimators must match coil selections to the schedule on the drawings, since a heating versus cooling coil or a different row count changes the unit and its hydronic connections. Overlooked condensate and valve packages are common bid gaps.

Example

Pricing rooftop units, the estimator confirms each cooling coil's listed flow rate and rows on the equipment schedule, then carries the matching control valves, condensate piping, and insulation in the mechanical bid.

Related Terms

Air HandlerChilled Water SystemHeat ExchangerFan Coil Unit

Frequently Asked Questions

A heating coil raises supply-air temperature using hot water, steam, or electric resistance. A cooling coil lowers air temperature and removes moisture using chilled water or refrigerant, producing condensate that must be drained. Cooling coils therefore require a condensate pan, trap, and drain piping that heating coils generally do not, affecting installed cost.
Beyond the coil or the unit it sits in, price the supply and return piping, isolation and control valves, balancing valves, strainers, insulation, and for cooling coils the condensate drain, trap, and pan connection. Controls and sensors tie into the building system. Matching these to the equipment schedule prevents scope gaps at buyout.
Entering and leaving air temperatures and humidity, along with water flow and temperature, define the required heat transfer and thus the coil's size, row count, and fin spacing. A larger temperature difference or higher airflow demands more capacity. Estimators rely on the engineer's scheduled selections rather than resizing, but verify the schedule matches the specified equipment.

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