Frequently Asked Questions

For over 75 years, HOTSTART has been helping customers pick the heater that will serve their needs best. Below are some frequently asked questions with answers that can guide you in your selection process. If you have any questions or would like to talk to one of our customer service representatives, call 509-536-8660 and our team will walk you through selecting a heater for your project.

All internal combustion engines and their components are designed from the factory to operate within an optimal temperature range, including pistons, cylinders, bearings, and lubrication oil. While the engine is running, the engine’s dedicated cooling system acts as the safeguard to ensure this temperature range isn’t exceeded.

When an engine is shut down or is in standby, these components will gradually cool to the ambient temperature, whether it’s a room-temperature facilities area, an outdoor generator enclosure, a locomotive rail yard in the winter, or a mining operation in the far north. Without a dedicated heating system that preheats and circulates critical fluids, an engine must bring itself up to optimal temperature before accepting a heavy load, or risk unnecessary wear and tear. Each time the engine is started back up again from a cold start can cause costly problems over time, including increased emissions, lack of lubrication, and other issues. To help avoid these problems, engines may be idled continuously during downtime—but that comes with the drawbacks of wasting fuel and increasing costs.

Continuously heating an engine during downtime, or preheating immediately before starting, eliminates cold starts and the problems encountered from repeated hard starting—without wasting fuel or shortening the engine’s operating life. When your engines are critical to providing key services, such as applications in data centers, hospitals, airports and fleet vehicles—engine heating systems are the first step to ensuring reliability and maintaining your bottom line.

While most of us think of cold engines in the extreme winters of the arctic or high-altitude mining sites, the need for engine heating systems can be found in any location that falls below a typical engine’s operating temperature – usually any temperature lower than about 100 °F (38 °C). A data center in the tropics is just as likely to employ an engine heating system as one in a cold climate—as the system will need to keep the engine warm during the night when the temperature falls, or during brief cold spells during the normal season. Additionally, engine heating systems can also be found in relatively warm, high-humidity environments such as shipping ports or coastal gas compression facilities to prevent condensation from developing in the engine cylinders and oil sumps during standby periods.

In short, engine heating systems are a cost-effective solution to promote maximum engine reliability and operating life—no matter what the current conditions are.

HOTSTART heating systems come with a wide range of model and heat power options, so selecting the right system for your engine may seem overwhelming.

Heat power is almost always the most important consideration. Too little heat power, and your engine heater will struggle to keep the engine block at the optimal temperature—incurring a lot of electrical costs in the process. Too much heating power, and you may be paying for heat power you simply don’t need—while shortening the life of your hoses and seals at the same time.

When selecting your heating system, it’s best to have a good understanding of your engine size and the overall amount of coolant in the engine’s water jacket. You’ll also need to take the following factors into consideration:

The lowest temperature you expect your engine to be exposed to

  • If your engine may be subjected to wind or other factors that will reduce heating effectiveness
  • If you intend to use multiple systems (coolant and oil or a dual-fluid system) to heat the engine
  • If you intend to install either a thermosiphon (convection-based) or a forced circulation (pump-driven) heating system

For thermosiphon heaters and HOTflow® heating systems, these factors can be simplified into one basic rule that uses the engine displacement size and the lowest expected temperature as a starting point. For most small- or mid-sized engine applications (5 to 50 liters), this rule will produce a good working estimate for heating power.

  • If your engine location’s temperature will remain above 0 °F (−18 °C):

o   3 × [your engine’s cubic inch displacement] = your heater’s wattage requirement, or

o   183 × [your engine’s liter displacement] = your heater’s wattage requirement.

  • If your engine location’s temperature will fall below 0 °F (−18 °C):

o   5 × [your engine’s cubic inch displacement] = your heater’s wattage requirement, or

o   305 × [your engine’s liter displacement] = your heater’s wattage requirement.

For larger or more complex applications, especially those requiring multiple heating systems, larger volumes of liquids or other factors, it’s best to work with a HOTSTART representative directly to specify the heating system that will provide the heat power you need.

You can reach our customer service team directly at 509-536-8660 or contact our Customer Service team to get started.

HOTSTART heaters are designed to accommodate small installation spaces, using a minimal footprint area while providing maximum heating power. Depending on the type of heater, they may be either threaded into the block directly or externally bracket-mounted, foot-mounted, or plate-mounted.

In most cases, HOTSTART does not recommend fastening heating systems directly to the engine itself. When exposed to engine vibration without dampening, heating systems can suffer problems over time, including electrical connection problems or leaking. The exceptions to this rule include in-block heaters or oil heaters (OW/OE series) as they must be installed directly in the water jacket or oil sump.

For external heating systems, HOTSTART recommends installing the heater on a vibration-isolated skid or in a similar location protected from engine vibration. The HOTSTART CTM heating system offers an optional vibration isolation kit which allows for installations where vibration isolation may not be available, such as a vehicle engine bay or a confined generator enclosure.

Full-flow isolation valves are also a good idea to add to a heating system’s plumbing during installation, as these valves will allow the heating system to be serviced later on without requiring that the engine coolant be drained.

Heating system orientation is also an important consideration, especially when identifying a good installation location for a heating system. Some systems, such as the TPS, CTM and CSM, have a single orientation option. However, the TPS and CTM are designed to allow the inlet and outlet ports to be adjusted to make hose routing easier. 

Other HOTSTART heating systems, such as the CKM and our Tank-Style heaters (CB/CL, SB/SL, WL and EE series) may be mounted either horizontally or vertically. Note that vertical installations will require care when routing hoses as all dips and horizontal hose runs must be eliminated to ensure air pockets cannot form. In rare cases, Tank-Style heaters may also be mounted at a slight incline, raising the outlet above the inlet, to promote heated fluid flowing through the system and resolve fluid flow issues. To properly install your heater, please refer to your model’s installation instructions.

Direct immersion heaters, including the OW and OE series of oil heaters, should be mounted on the side wall of a fluid tank or sump with a minimum clearance from the bottom of the container to avoid issues with sediment build-up. Immersion heaters must always be fully immersed in fluid during heating to avoid burning out the heating element. Also, immersion heaters must never be installed pointing upward from the bottom of a tank or sump, as the heating element may be exposed to air if the fluid level changes.

Some direct immersion heaters, such as in-block heaters, are designed for a specific engine port and must be installed in this location for proper operation. That port location can be found by referencing your model’s installation instructions.

For coolant heating systems that are installed externally from the engine water jacket, such as thermosiphon heaters or HOTflow® heaters, port selection plays an important role in ensuring heater longevity and reliability. There are two ports on the engine that should be dedicated to the heating system: the supply port and return port. Both ports must meet the minimum required size for the heater you intend to install. Check your heater’s installation instructions for minimum port size requirements.

Supply Port

The supply port allows cold coolant to flow from the engine to the heating system. The supply port should be located as low on the engine’s water jacket as possible to ensure that the coldest coolant is being drawn into the heating system. For most engine configurations, the ideal lowest point is located toward the front of the engine, near the lower radiator hose.

Return Port

The return port allows heated coolant to flow from the heating system back into the engine’s water jacket. This port should be located high on the engine’s water jacket for two main reasons:

  • Placing the return port high on the engine ensures it is as far away from the supply port as possible. Placing the two ports apart ensures that coolant travels through the entirety of the engine block, reducing extreme hot spots and cold areas.
  • Placing the return port high on the engine block ensures that heated coolant travels downward through the engine water jacket as it cools, flowing with gravity rather than fighting against it. While placing the return port low on the engine jacket will result in heated coolant traveling upward, in most cases this heated coolant will cool rapidly and begin flowing downward before it can reach the top of the water jacket, creating cold areas and reducing heater effectiveness.

The return port must also be positioned away from the engine’s thermostat, which is typically located near the top radiator hose and toward the front of the engine. If placed near this thermostat, the heated coolant from the return port may trigger the engine thermostat, permitting heated coolant to flow to the radiator instead of the engine block. Warm coolant traveling through the radiator will cool rapidly and will result in drastically reduced engine heating as the radiator continues to move heat away from the engine block.

Placing the return port high near the rear of the engine block removes the possibility of triggering the engine thermostat and ensures that its location is as far from the supply port as possible, maximizing engine heater effectiveness.

For V-type engines, fluid flow across the entire engine block is important. To promote cross-flow, the supply port may be installed on the opposite side of the engine as the heater. By drawing from the lowest point on the opposite side, heated engine coolant will flow across both the length and width of the block, further maximizing engine heater effectiveness while minimizing heat loss. If the return port is located on the opposite side of the engine instead of the supply port, the extended return hose length may increase heat loss and result in dips and bends that may collect air pockets—potentially reducing heating effectiveness and heating system longevity.

For Thermosiphon, HOTflow® heaters, and larger forced circulation systems, making sure your plumbing lines and fittings meet the minimum size requirements will ensure maximum flow of heated fluid throughout the engine block, sump or compressor.

Thermosiphon minimum port fitting sizes:

TPS 500 - 2000 watts 3/8 inch NPT
CB/CL/SB/SL 1500 - 3000 watts 1/2 inch NPT
CL/SL 4000 - 6000 watts 3/4 inch NPT
WL/EE 1500 - 5000 watts 3/4 inch NPT


Thermosiphon minimum hose inner diameters:

TPS 500 - 2000 watts 5/8 inch
CB/CL/SB/SL 1500 - 3000 watts 3/4 inch
CL/SL 4000 - 6000 watts 1 inch
WL/EE 1500 - 5000 watts 1 inch


HOTflow® minimum port fitting sizes:

CTM 1000 - 2500 watts 3/8 inch NPT
CKM 3000 - 6000 watts 3/4 inch NPT
CSM 3000 - 12000 watts 3/4 inch NPT


HOTflow® minimum hose inner diameters:

CTM 1000 - 2500 W 5/8 inch
CKM 3000 - 6000 W 1 inch
CSM 3000 - 12000 W 1 inch


Forced Circulation Heating Systems

Plumbing requirements for forced circulation heating systems vary by model, depending on the system configuration, installed pump and fluid type. Check your Installation & Operation Manual for your specific minimum requirements. However, all forced circulation systems will require that:

  • At a minimum, the supply line must be the same size as the pump inlet. HOTSTART recommends using the largest practical inner diameter size hoses to maximize flow.
  • The suction port for coolant systems must be installed as low on the engine’s water jacket as possible.

The suction port for oil systems must be installed as low as possible in the engine or compressor oil sump. However, it must not be installed on the bottom of the sump or in a location low enough that may allow debris or sediment to enter the heating system. HOTSTART recommends installing a swing-type or full-flow check (non-return) valve as close to the suction port as possible to prevent oil flowing back into the sump.

Ordering a HOTSTART heater is quick and easy.

First, select the heater you’ll need for your application. You can specify a heater using the following resources:

  • For in-block heaters, use our In-Block Heater Tool.
  • For a product overview, read the Which heater is right for my application? FAQ post.
  • For a list of our most popular models, view our Product Catalog.
  • Search and filter our product listing with our Product Search.
  • Contact our Customer Service team directly to select a heating system.

Once you know the heater model, operating characteristics or part number, you can purchase a heating system by:

  • Contacting our Customer Service team to order direct from HOTSTART.
  • Working with one of our worldwide HOTSTART Distributors.
  • Ordering through your local OEM HOTSTART Dealer, including Cummins, Detroit Diesel, Generac, Kenworth, Kohler, MTU Onsite Energy, and Peterbilt.

Heater installation procedures and tools vary depending on the type and model heater you are installing. However, there are some basics to expect for each installation. At a minimum, you should expect to prepare the installation by draining the coolant and/or lubrication oil from the system before installing the heater. You’ll also need to have selected the supply and return ports on the engine block or sump to meet the placement guidelines and minimum size requirements. For thermosiphon or HOTflow® installations, you’ll need to run the engine to purge air from the system before energizing the heater for the first time, so make sure you have access to start the engine once the heater is installed.

Before installation:

  • For coolant heating systems, drain the coolant from the engine block and radiator
  • For oil and dual-fluid systems, drain the lubrication oil from the sump or pan.
  • Select engine block or sump ports for each heating system's supply and return port
  • Select a heater installation location and add appropriate vibration isolation if necessary
  • Plan the hose routing from the heater installation location to each port

General tools:

  • Basic mechanic’s tools, including drivers, wrenches and sockets.
  • Basic electrical tools
  • Basin or bucket, rags
  • Eye protection and gloves


  • Hoses (see your instructions for minimum inner diameter)
  • Port fittings (see your instructions for minimum sizes)
  • Full-flow isolation valves (recommended for maintenance)


  • A plug-in or hardwired power source with suitable grounding that is compatible with your heater’s specification
  • Power disconnection point (recommended for all hardwired heaters)
  • A 24-volt engine run signal source for remote automatic operation of CSM models and industrial forced circulation systems (typically the engine’s fuel pump)
  • For all three-phase systems, or single-phase systems requiring a contactor and/or transformer, a customer-supplied control box (check your model's installation instructions)
  • All additional electrical components as recommended by your model’s instructions, such as a liquid level switch for industrial immersion heaters


  • A laser or infrared thermometer or similar tool to check for operation/troubleshoot installation

For In-Block, Thermosiphon, and HOTflow® heaters, HOTSTART installation instructions recommend running the engine until it reaches operating temperature before energizing the heater for the first time.

When an engine is run to operating temperature, the engine’s thermostat opens, allowing coolant to flow through the radiator and return to the engine block. During this process, the engine’s water pump will move coolant throughout the engine block to the radiator and any air present will be purged from the system.

By using your engine’s own method of removing air from the cooling system, you will ensure that the engine’s water pump moves coolant throughout the entire system — including the newly installed heater and plumbing lines — and flushes out any air pockets or bubbles that may have developed during the installation process.

If these air pockets remain when the heater is energized, they may block the flow of fluid to or from the block. This lack of flow may cause the heating element to boil coolant, creating a larger air pocket and exposing the element to air. An element exposed directly to air may fail immediately, requiring either an element replacement or replacement of the entire heating unit.

It's quick, it’s easy — and it’s the best way to ensure your heating system is ready from day one. If you have additional questions about installing and running your heater for the first time, contact our customer service team.

For fleet vehicles with in-block heaters or direct immersion oil heaters installed, the question of saving money often hinges on the weather—since the heaters incur electrical costs if they are plugged in, whether the engine needs to be heated or not. If equipment operators plug them in every night regardless of conditions, you could be paying a lot of unnecessary electrical costs. However, leaving it up to the equipment operators or timers to activate them can result in hard starts the next morning if temperatures dip unexpectedly, or worse, they aren’t plugged in at all.

The TwinStat™ cord is an easily implemented solution for this problem. Heaters equipped with this cord will only activate if the outside temperature dips below 40 °F (4 °C). If the spring or fall temperatures stay warm, the heaters stay off and use no electricity. If temperatures fall, the cord automatically energizes the heater, safeguarding the equipment and providing all the benefits that come with engine heating—including easy starts the next morning.

In a typical backup generator application, the generator will likely consume far more energy over the course its operating life than it will produce. One of these likely factors is the engine heating system, installed to meet the NFPA 110 standard for emergency and standby power systems which specifies that a generator must be capable of assuming a full load within ten seconds of the engine start.

To satisfy this requirement, many factory-built gensets are equipped with a single or dual thermosiphon engine heating system. These heating systems can provide the necessary engine heating to ensure the genset meets load requirements; however, their circulation method is less efficient than a comparable pump-driven unit. In many cases, if a genset is equipped with dual thermosiphon heaters, they may be replaced with a single pump-driven unit.

Because a thermosiphon heater relies on convection to circulate the fluid, the heating element must heat the fluid to a very high temperature to produce flow. Over the lifespan of the heater, this increased power demand can add up. Additionally, the higher temperatures produced by a thermosiphon heater may require that plumbing hoses are replaced more frequently, also adding to total ownership costs.

In these cases, replacing a legacy convection-based heating system with a forced circulation system—such as a HOTSTART HOTflow® heater—can lower electrical costs drastically, in some cases up to 35%. Replacing two convection heaters with a single heater also reduces overall system complexity and may lower maintenance costs. Finally, plumbing lines are not exposed to the high temperatures required by thermosiphon circulation and will last longer between routine maintenance, further reducing maintenance time and costs.

To learn more about HOTflow® and our other forced circulation heating systems, visit our HOTflow® solutions page. Technicians interested in becoming HOTflow® certified for installing these types of systems should refer to our HOTflow® Technician Certification Training page for information on attending our webinars.    

HOTSTART is dedicated to superior service over the lifetime of your heater. As a part of that commitment, we make servicing and replacing parts simple. You can order replacement parts for your HOTSTART heater using any of the following options:

  • Contact our Customer Service team and order direct from HOTSTART.
  • Work with one of our worldwide HOTSTART Distributors near you.
  • Purchase through your local OEM HOTSTART Dealer, including Cummins, Detroit Diesel, Generac, Kenworth, Kohler, MTU Onsite Energy, and Peterbilt.

When ordering replacement parts, be sure to reference your heating system’s model number and/or serial number found on the identification plate.

Our larger forced circulation systems, including those intended for use in Oil & Gas applications or Marine engine systems, are equipped with connections enabling fault signals and operating states to be transmitted to a user’s system interface—giving them up-to-date information on the heating system’s status and health.

For users of smaller systems, evaluating heating performance can be done with a few extra tools. In some cases, a malfunctioning heater can be remedied with a little care. In other cases, a heater’s performance may be significantly improved.

For Thermosiphon heaters, the process can be more challenging as circulation occurs by heating action alone. However, once installed, a thermosiphon heater should begin to warm the return hose. Technicians can immediately detect this heating action by touch, confirming that heated coolant is flowing into the engine block.

If you have an infrared laser thermometer, the temperatures of the return hose, supply hose, heater tank, and engine block can be confirmed. By using an infrared camera or recording device, you can take this troubleshooting one step further by capturing images of the pattern in the heater and engine block. These infrared recording devices are excellent tools for both troubleshooting problems as well as improving heater installations, since they can detect both hot spots and cold areas in both Thermosiphon and HOTflow® applications.

Common issues include:

No heat from the heating system. If the temperature of the fluid happens to be above the heater’s thermostat range—either due to a warm ambient temperature or a recently run engine, no heating will take place until the fluid cools below that temperature. No heat may also mean no power, so check the power source and heater cord for damage. If the system still produces no heat, the thermostat or element should be tested to make sure they are operating normally.

Continuous heating. Thermosiphon systems normally cycle about four times per hour. If your heater is continuously on without cycling off periodically, it may mean that either the heater isn’t powerful enough for the application or the engine is losing heat faster than the heater can circulate it through the engine block. Unexpected low temperatures, exposure to high winds, or excessive heat loss through the radiator can affect heater performance. If you suspect your heater’s return port is located too closely to the engine thermostat, you can check for heat loss to the radiator by using an infrared thermometer or camera.

If you continue to have problems with heater operation, or you are looking for installation and operation tips or help, contact the HOTSTART service team directly for service and support.