How the Fire Tube Boiler Runs

The Lochinvar Fire Tube Boiler runs efficiently and smoothly, and stays running without frequently turning on and off. An FTX500 fires at its maximum 500,000 Btu/hr rate when heat load is highest, then gradually goes as low as 10% (50,000 Btu/hr). The boilers have a fiber burner that controls the temperature.

  • Up to 98% thermal efficient
  • 10 to 150 GPM flow rates
  • 5 models from 399,000 to 850,000 Btu/hr
  • Up to 10:1 turndown ratio

Standard Technology

The fire tube boiler has been redefined by Lochinvar, leveling up both residential and commercial models. These new models have a range of 399,000 to 850,000 Btu/hr, and the FTXL has impeccable thermal efficiency and footprints.


The boiler introduces boiler plant control from anywhere with Lochinvar’s all-in-one SMART SYSTEM. The SMART SYSTEM can be paired with the Building Automation System and the CON-X-US® mobile communication system, the latter of which allows you to oversee many FTXL boiler plants without having to go to them in-person.

Additional Features

Fuel Costs & Ease of Installation

The FTXL Lochinvar boiler saves you fuel costs based on building load of about 19,000 therms/year, and here’s what that looks like over a three year period:

A bar graph with three year fuel savings.

From Lochinvar: “Fuel savings is based on a heating load of 19,000 therms per year being supplied by an 82% efficient boiler at the DOE National average for natural gas of $1.09.”

The Lochinvar fire tube boiler also has easy installation due to its size (6.2 sq. ft), and all connections behind the unit. The connections are covered by doors, which allows for simple access.

Outdoor Sensor & Flexible Vents

The fire tube boiler’s outdoor sensor cuts down on time and money, and it has a range of about 2,000 feet line-of-site.

There are six venting options in the fire tube boiler: room air vertical, room air sidewall, direct vent, common vent, direct-vent vertical, and vertical with sidewall air. Multiple units can have common vents, which eliminates time and money.

LCD Interface (Multi-Colored) & USB Drive

The Lochinvar fire tube boiler has three colors on its LCD interface. In addition, there is a USB drive that allows for easy management and quick uploads.

Lochinvar Fire Tube Boiler Offers Peace of Mind

There are two operation options: “Lead-Lag,” which has one boiler become the lead boiler, and “Efficiency Optimized,” which runs both boilers at the same time.

The Lead-Lag operation has one boiler that goes to capacity on-demand, and the second picks up additional lag. Every day, the one that starts and the one that picks up lag switches. The lead boiler can be switched off for maintenance, and the second one will become the lead boiler. This will decrease stress because one boiler will still run.

For the optimizing efficiency operation option, both boilers run at the same time and at the same rate.

Oslin Nation Are Lochinvar Distributors

We are a Lochinvar boilers and water heaters distributor. Contact us for more information.