HVAC

How Does A Diesel Or Gas Heater Work? (Explained!)

Diesel Or Gas Heater

How Does A Diesel Or Gas Heater Work? (Explained!)

RV diesel and gasoline heaters both operate by combusting or igniting fuel mixed with air to provide heat to a heat exchanger, which heats the air (or water). However, a gasoline engine uses a spark to ignite the fuel and air mixture, while a diesel engine uses pressure to ignite the fuel and air mix.

How Does A Diesel Or Gas Heater Work? (Explained!) 1

To speed up the process of ignition in a diesel heater, systems often use a glow plug to preheat incoming air so that the fuel will ignite more quickly. Other diesel heaters simply burn the fuel either via a wicking system, igniting it using a sparking igniter. These tend to be less efficient, produce more pollutants into the interior air, generate more airborne soot, and are more difficult to manage heat output.

Are Diesel/Gas Heaters Safe?

Mounted RV diesel heaters are exceptionally safe while gasoline heaters, properly installed, are also quite safe. Both vent exhaust directly to the outside. Because diesel ignites under pressure, it is a much safer fuel to store, even in open containers, while gasoline may spontaneously combust If there are fuel leaks in the unit or lines into the heater inside the RV, those leaks pose a significant risk, but still are much safer than propane units.

How Does A Diesel Or Gas Heater Work? (Explained!) 2

Diesel heaters produce less carbon monoxide than gasoline or propane heaters, have higher fuel efficiency, and generally have automatic shutdowns to prevent overheating and fires. Every modern diesel heater on the market is also designed to use biodiesel, which, aside from the increased sulfur dioxide emissions, is a cleaner fuel, without the heavy metal emissions associated with regular fossil fuels.

An important consideration for RVers is the quantity of fuel that you can transport and the rules about containers. The US DOT (US DOT bulletin, 2020) allows you to carry either 5- or 8-gallon jerry cans of gasoline, or up to 440 pounds, in approved containers, but is far less rigid on diesel fuel, since it is combustible, rather than flammable.

What Are The Differences Between A Diesel And A Gas Heater?

There are four primary differences between a diesel and a gasoline heater:

  1. Diesel systems produce combustion by pressure, while gasoline systems use a spark to combust the fuel
  2. Diesel systems produce more heat than gasoline fuelled heaters
  3. Diesel systems produce more noise and more odor, at start-up than a gasoline system
  4. Gasoline systems can operate without special equipment at higher altitudes, and, sometimes, in colder weather, than diesel, due to the viscosity of diesel fuel.

Does One Fuel Burn Hotter Than The Other?

Diesel burns the hottest of the three main fossil fuels used in RVs and campers: propane, gasoline, and diesel. Diesel creates 137,000 BTUs of heat, gasoline creates 120,000 BTUs, and propane 91,500 BTUs. Kerosene, having many of the properties of diesel, produces 132,000 BTUs. Kerosene burns less rapidly than diesel, however, but costs more per unit.

To calculate the cost per heating unit, you will need to determine the purchase price of each of the fuels and convert it to cost per BTU unit. Thus, there may be instances where price variations of fuel types will make a lower BTU fuel more cost-efficient than a higher BTU fuel. That translates into more heat per dollar, but not more heat per unit of fuel.

Can You Use Gasoline In A Diesel Heater And Vice Versa?

The fuels generally are not interchangeable in your heater, but some brands, such as the maxpeedingrods air heater can use a variety of fuels, including gas, kerosene, propane, and most other diesel units will burn gasoline.

However, since gasoline is less viscous, or thick, than diesel, the orifices through which the fuel is delivered to the combustion unit are smaller. Diesel tends to clog these orifices more readily, particularly at a lower heat, when diesel is even more viscous. In the short term, it will work but is not recommended.

On the other hand, gasoline-burning in a diesel system uses more fuel more quickly, creates an unburned fuel odor, and burns much louder, because the fuel is less viscous and an excess of fuel pours through the nozzles into the burn chamber. There also is a risk of damage to the unit if leaks or drips occur, with gasoline accumulating and possibly exploding prematurely. That is similar to pre-ignition in a car engine. Diesel in a gasoline engine leaves sooty deposits more readily than gasoline.

Webasto, one of the largest manufacturers of diesel and gasoline parking heaters in the world, makes both diesel and gasoline heaters but does not offer one that burns both fuels.

Do You Need A Separate Tank Or Can You Just Connect One Fuel Source?

A gasoline heater can be run off the gasoline in your motorized RV’s gasoline fuel tank, and a diesel heater can run off the diesel in your RV fuel tank if it is a diesel engine. When doing so, owners should have a low fuel monitoring system in place to alert them to depleted fuel levels in the main tanks.

Often, RVers install diesel or gasoline heaters so that they can boondock, camping off the grid. This also suggests that the camper often will be distant from service stations and retail fuel outlets, so running low on fuel for your RV engine can be a critical issue.

If you opt to install a separate fuel tank for your heating system, consider diesel as your best option, even though fewer service stations carry diesel than the number of outlets carrying gasoline. Storing supplemental gasoline inside your camper is very risky, but diesel, being less volatile, is more readily stored in the camper unit.

When boondocking, recognize that, at higher elevations, diesel systems struggle more, because they rely on pressure to ignite and for the fuel to flow, while, in the mountains, air pressure is reduced. Most modern diesel heaters have equipment built into them that compensates for this factor, though.

Can Diesel Heaters Produce Different Levels Of Heat?

RV diesel heaters can produce different levels of heat, in the same way, that any other fossil fuel system is controlled. In open systems, like Buddy heaters, the ability to control the heat is more limited, amounting to a simple two- or three-position switch to control fuel output for the wicking system, similar to that on a propane radiant heater, or a dial control similar to a kerosene lantern. These are manually controlled, and not ideal for maintaining a uniform temperature.

Cheaper fixed-mount RV heaters also may lack a full-range control system, but the vast majority of RV diesel heaters and diesel air/water heaters (RVChronicle.com. 2022) operate with an efficient thermostat control system, allowing the owner to adjust and even program heat from a central thermostat.

Can You Use Your Existing Thermostat For A Diesel Heater?

You can use your RV’s existing thermostat, with modifications, for a diesel heater and even use a low voltage or millivolt thermostat (but not line voltage) in your RV. However, there are minor modifications necessary, depending upon the age of the thermostat and the make of the heater.

For instance, a “Sleep” mode may be necessary for your new heater to work, so that the thermostat knows to first “wake” the diesel heater to preheat the air for combustion. Other than that, you can even wire in a system that has multiple modes, sleep times, varied temperature settings, and so on, as in your home.

The purpose of the thermostat merely is to send relevant signals to the heater, telling it whether it should be on, off, or getting ready to start up. The thermostat relies on the thermometer and the range of temperatures around each setting (generally 1 to 3 degrees Celsius) to determine if it should send a “start” signal to the unit, or a “shut off” signal.

How Much Power/Electricity Does A Diesel Heater Use?

A typical diesel heater draws between 0.8 and 2.5 amps of 12-volt DC energy when running and up to 3.5 amps of surge energy when starting. This is a minimal amount of electricity and likely will not impact severely on your battery overnight. In any event, you should have a separate battery for operating 12-volt systems in your RV when the engine is not running, so that you do not drain your starting battery for the engine inadvertently.

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