Natural Draft


TERI Natural Draft Horizontal Heaters

TERI horizontal water-bath heaters are commonly used in applications where process temperatures do not exceed 170°F, including utility, gas processing, refining of oil, and gas and other industrial applications. Our Natural Draft Horizontal Heaters are custom designed and engineered for each application and can be designed in single, double, or triple-burner configurations. TERI Natural Draft Horizontal Heaters are ideal for remote locations and locations with limited power supply.

With capacities from 1 MM Btu/hr up to 15 MM Btu/hr, our expert team can conceive and construct the right TERI Horizontal Heater for your needs. TERI heaters are designed in both forced draft and natural draft models to accommodate working conditions, environmental compliance, and power availability.

170620 ISO
170620 GT SIDE
170620 new iso

Ideal Applications

  • Heating natural gas prior to pressure reduction to eliminate hydrate formation downstream of expansion valving
  • Heating well stream fluids prior to phase separation.
  • Heating process streams to maintain fluid viscosity at a minimum to reduce HP pumping requirements
  • Heating turbine fuel gases to meet manufacturer's temperature requirements
  • Vaporization of liquid propane

Heater Operation

The process fluid to be heated flows through a serpentine-configured coil that is mounted in the upper portion of the heater shell. A controlled amount of heat is released into the firetube (combustion chamber) which is located in the lower section of the heater shell. This heat is efficiently transferred from the firetube to the bath media. The heat contained in the bath media is then transferred by natural convection into the process stream which flows through the process coil.


  • Plasma-cut, shop-fabricated components
  • Individually removable firetubes
  • 304 SS flue gas stack or stacks
  • Stack clean-out tee
  • Flue gas stack anti-reverse draft diverters with train cap and bird screens
  • "Pilot in a Drawer" assemblies for easy maintenance and inspection
  • Basic electric and pneumatic in addition to PLC control systems
  • Multi-mitered firetube bends (no single miter cut to greater than 22.5°)
  • Positive seal flange designs
  • Bath liquid expansion reservoir designed to hold 7% of the total bath media
  • Bath liquid level gauge
  • Bath temperature indicator
  • Shell designed in accordance with API 12K
  • Coil designed and stamped in accordance with ASME – 8-1
  • 100% radiography on process coil welds
  • Process coil built to ASME Section VIII, Division 1 and National Board stamped


TERI heaters, available in forced draft and natural draft, are composed of the following components, each designed to meet specific design criteria:

  • The Heater Shell is an atmospheric vessel designed in accordance with API 12K requirements. The shell contains the process coil, firetube (combustion chamber) and heat media.
  • The Firetube is commonly of the U-tube configuration. The tube is removable and designed to efficiently transfer heat into the surrounding heat media and to minimize flue gas friction losses.
  • The Process Coil is a pressure-containing part commonly designed in accordance with API 12K or ASME Section VIII Division 1 code requirements.
  • The Flue Gas Stack is designed to provide positive flue gas flow (draft) by overcoming the friction losses in the complete combustion system.
  • The Heat Media is commonly a mixture of inhibited ethylene or propylene glycol and water which is blended to a consistency to provide the proper freeze protection for a given application.
  • The Expansion Tank is designed to reduce internal corrosion within the heater shell by keeping the heater shell liquid packed and moving the wet dry interface of the expanding bath media from the heater shell into the expansion tank. The expansion tank is designed to contain 100% of the expanded bath media from a temperature of 40˚F to the maximum operating temperature.
  • The Fuel Gas Train is built to API 12K. Larger duty heaters are ASME standard as a guideline in addition to API 12K.


TERI horizontal heaters are available with a wide variety of accessories to meet customer specified mechanical and operational requirements, including simple pneumatic controls or sophisticated remote control and monitoring equipment.

Optional Control Enhanced Designs

  • Pneumatic-controlled equipment operation
  • Electrical-controlled equipment operation
  • Combination pneumatic and electrical controlled equipment operation
  • Flame-safeguard assemblies including pneumatic 120VAC, 24VDC, 12VDC, or solar power
  • Manual or automatic pilot ignition designs

Optional Fabricated Enhanced Components

  • Cushioned (electrically-insulated) process coil supports and tube sheets
  • Shell treated with water-soluble rust prevention coating
  • Customized heater supports to meet existing pier locations
  • Hot-dipped galvanized heater skids, ladders and platforms