IDF Oil/Diesel Service

IDF LP/NG Service

IDF Oil Troubleshooting


Frequently Asked Questions

Help! I have never seen a Frost-Fighter Heater before.

A lot of technical support calls we get from you sound like this one. Don’t worry. A portable heater is a machine like any other. Once you understand how the unit should work, you can start to understand the troubleshooting process. At Frost-Fighter, we have been making portable heaters for over 20 years under the “Frost-Fighter” name, but others since 1975. There have been different models and technologies used along the way. Here are some explanations of our current popular models.

DF (Direct Fired)

A direct fired heater is the simplest method for heating and the easiest to explain. Imagine you have a propane or natural gas torch. In order to get the flame you provide a spark and turn on the fuel. Now add a larger burner and a fan to move the heat. This is the basics of a Direct Fired unit. The fuel is ignited and the heat and fumes are blown out the end of the heater. Direct Fired heat is the least expensive and most efficient form to provide a lot of heat.

IDF (Indirect Fired)

An indirect fired heater is only slightly more complicated. Instead of igniting the fuel directly in the airstream that enters the space like the DF units, it is ignited in a combustion chamber. The heat generated is transferred to the airstream passing over the chamber and the fumes are exhausted out the top of the chamber through a chimney flue. This provides the cleanest heat for the space since the fumes are exhausted separately from the hot air.

IHS (Indirect Fired High Static)

An indirect fired high static heater is exactly the same concept as a standard IDF heater. They still ignite fuel in a combustion chamber. The heat generated is still transferred to the airstream passing over the chamber and the fumes are still exhausted out the top of the chamber through a chimney flue. The only difference in operation is that the fan to push the air over the heat exchange can handle more static or backpressure. This allows for longer ducting. Typically the requirements for longer ducting are also coupled with a larger heating requirement as well. That is why the IHS units have the highest heating capacities of all of our indirect fired units.


Typically there are two main types of fuels for industrial portable heaters. The first is gases. Propane and natural gas are the most common gases used for heating. The other type of fuel is oil based fuels. Heating oil, diesel, kerosene and some jet fuels can be used in an oil heater. No fuel like crankcase oil or heavy oils can be used.

How does the IDF blower fan work?

The IDF blower fans, whether the unit is a LPNG or Oil, all have the same electrical control circuit. When the power comes in from the electrical cord, the power is routed directly to the fan switch at the front of the unit and then to the fan motor. The fan switch is located under the 8”x3” galvanised cover at the duct discharge end of the unit. You can identify the fan switch from the other switches under the cover since the fan switch is the only switch that has a temperature set point.

You can adjust the temperature at which the unit will turn the main fan on. The range is usually between 90°F and 130°F. When the surrounding temperature is lower, the fan switch should be set higher. This will help the unit from cycling the main fan so often.

So when the heat exchanger builds up enough heat to “make” the setting on the fan switch, the blower motor will have power and turn on.

Note: If the unit is plugged in, the fan will start if the air inside the unit is warm enough to engage the fan switch. This can be unexpected it the unit is un-plugged and the plugged in quickly. The main switch “MANUAL/OFF/THERMO” for the unit can be in any position and this will still occur.

How does an Oil burner work?

Before we get in to how the burner functions, let’s review the combustion process. In order for any combustion process to take place, you need 3 elements.

  1. Air to provide oxygen
  2. Fuel to burn
  3. Spark/ignition source

To have efficient combustion, these three elements are required to be in balance. Take one away and the combustion process fails.

The IDF Oil burner is simply a system that controls the combustion process. A motor powers a fan to provide air and a pump to supply fuel. The fuel is turned on and off with a solenoid valve. Meanwhile the igniter provides the spark. To determine if the flame is present, a CAD cell senses light and sends a signal to the controller. This controller coordinates the activities between the components in the burner system. If anything is not happening in the right order, the controller trips the alarm.

There are a number of checks that are required for the burner to fire. The first is a safe start. Once the power is sent to the controller, either by selecting manual or a call for heat using a thermostat, the controller checks to make sure its internal system is okay. Then the next step is to purge the heat exchanger and burner with clean air. The fan engages and blows for 45 seconds. During this time, the igniter is activated. If there is excess fuel or the solenoid valve is open, a flame will be sensed by the CAD cell and shutdown the unit. If all systems are checked out, the unit will open the solenoid valve and try to fire for 15 seconds. This period is called the trial for ignition. Once the flame is sensed before the trial is completed, the unit will be able to transition to run mode.

How do I check the fan switch?

The reason you may want to check the fan switch is to identify the cause of the main fan not engaging. Since the fan switch is the only control component in the main fans electrical circuit, it alone controls the fan. To check the fan switch, you need to check for power at the switch. If there is 120V on one side of the switch, then there is no issue with the wires to that point.

With the power disconnected, add a jumper to the circuit, removing the fan switch. Once you turn the power back on, if the main fan turns on, then you know that the main fan is working properly.

Disconnect the power and reconnect the fan switch. If the fan switch does not engage the main fan when the unit is running, even when adjusting the set point lower on the fan switch dial, replace the fan switch.

Why is manifold pressure so important?

Nine out of ten times when we get a service call for a Propane or Natural Gas (LPNG) heater, we will be asking what is the current manifold pressure. In order to ‘hook up’ our units we say we need 7-14” W.C. or about ½ PSI. The problem with supplied pressure is that it is not a good indication of what the burner is actually seeing in terms of fuel. You can have 14”W.C. using a 3/8” line and the unit won’t fire because the volume of gas is not high enough to sustain the manifold pressure.

To check the manifold pressure, you need a manometer or other appropriate gage to check the pressure at the test port on the unit. It is located on a manifold elbow and is capped with a 1/8 NPT plug. Each unit has a different manifold pressure setting. Here are a few common ones:

  • IDF200 – 1.2” W.C. (LPNG)
  • IDF350 – 1.8” W.C. (LPNG)
  • DF400 – 1.4” W.C. (LP) – 3.5” W.C. (NG)
  • IDF500 – 2.8” W.C. (LPNG)
  • IHS700 – 2.9” W.C. (LP) – 3.7” W.C. (NG)
  • DF1500 – 1.5” W.C. (LP) – 3.6” W.C. (NG)

Which regulators should I use?