A line heater warms high-pressure wellhead gas before and across the choke so it does not freeze or form hydrates when its pressure is dropped. It is one of the most common pieces of equipment on a gas wellsite. This guide explains what a line heater is, how an indirect water-bath heater works, and what an operator monitors on it.
Line Heater in one line: A line heater is an indirect fired water-bath heater that warms produced gas or fluid flowing through a coil, using a fire tube to heat a water or glycol bath that surrounds the coil. It prevents hydrate formation and freezing when high-pressure gas is expanded across a choke, which chills the gas via the Joule-Thomson effect.
When high-pressure gas is throttled down across a choke or regulator at the wellhead, it cools sharply - the same Joule-Thomson expansion cooling used on purpose in a JT skid. At the wellhead, though, that cooling is a problem: if the gas contains water (which produced gas almost always does), the chill can form solid gas hydrates and ice that plug the choke, valves, and flow line, cutting off production. A line heater adds heat upstream and across the choke so the gas stays warm enough that hydrates and ice never form.
Line heaters are also used to warm crude oil or emulsions to reduce viscosity for flow, and to heat gas before it enters other processing. On gas wells they are essentially a freeze-prevention device that keeps a well flowing through cold weather and high pressure drops.
The defining feature is that the flame never touches the process fluid - it is an indirect heater. A horizontal vessel is filled with a bath of water (often with glycol to prevent the bath itself from freezing). Submerged in that bath are two things: a fire tube, in which a gas burner produces hot combustion products, and one or more process coils carrying the wellhead gas or fluid. The burner heats the bath, and the bath in turn heats the process coil. The bath acts as a buffer, spreading heat evenly and eliminating hot spots that would coke or damage the process fluid.
Process gas typically enters a preheat coil, passes through the choke where it is expanded and cooled, then flows through a reheat coil in the same bath to bring it back up to temperature before leaving. A temperature controller modulates the burner (often just on/off or high/low fire) to hold the bath temperature, and a low-water or high-temperature condition shuts the burner down for safety.
The key variables are the bath temperature (the primary control target), the process gas outlet temperature, the burner or pilot status, and the bath level. A flame-out, a low bath level, or a bath that is not reaching temperature all risk letting the process freeze up. Because the heater has an open flame in a hazardous area, its burner management and safety shutdowns are important, and remote sites make manual checking impractical.
A burner management system or RTU on the heater gathers these points. A cloud SCADA like Merobix reads the tags over Modbus or DNP3 and trends bath temperature, outlet temperature, and burner status across a fleet of unmanned wellsites, alarming when a pilot goes out, the bath cools, or the level drops - so an operator can relight or dispatch before a heater failure freezes a well off line, which is a common cause of lost winter production.
Because the burner flame does not directly contact the process fluid. The fire tube heats a water or glycol bath, and that bath heats the process coil carrying the gas or oil. This indirect design spreads heat evenly, avoids hot spots that would damage the fluid, and is safer than firing directly on a hydrocarbon stream.
It prevents hydrate formation and freezing. When high-pressure wellhead gas is expanded across a choke, it cools sharply and, with water present, can form solid hydrates and ice that plug the choke and flow line. The line heater warms the gas before and across the choke so it stays above the hydrate and freezing point, keeping the well flowing.
There is no single value - it is set so the process gas leaves warm enough to stay above its hydrate formation temperature after the choke, which depends on the gas composition, pressure drop, and ambient conditions. Baths commonly run well above freezing, and a temperature controller modulates the burner to hold the target while safety shutdowns trip on low water or overtemperature.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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