FS140 owners manual (pdf)                                     FS140 brochure (pdf)

FS140
Combo oil & wood forced hot air furnace.

Click here for FS140 Installation.
Click photo to enlarge.

The Benjamin line of Combination units, when used properly, will increase the convenience and pleasure you receive from heating your home with wood, and yet still give you the convenience and reliability of heating with fuel oil.

Because of the unique Benjamin wood burning design, which will utilize more of the BTUs available from each stick of wood, you will soon discover that you can reduce the amount of wood that you use to heat your home.
How does the Benjamin FS140 Furnace do this?
In several ways...

1. The unique combustion chamber.
   
2. Hand welded steel construction.
   
3. The heat exchanger passage design.
   
4. FS140 operational procedure.
   
   

• It's oval shaped.
  
• It's lacks firebricks or wood grates.
  
• It's thoughtful design and construction.
  

Hand welded, and constructed of 3/16", and ¼" thick steel, the combustion chamber is the heart of the unit. It measures 18" High, 21" wide, and 24" deep (This means that it can handle more than one 24" log!)

As you may already know, smoke contains much of the wood's total energy, and it wants to spiral by it's very nature. Benjamin has built a uniquely different combustion chamber and heat exchanger that facilitates that effect. A conventional square combustion chamber, or box frame heat exchanger restricts this natural flow. The smoke will rise up to the corners and swirl around there, cooling as it does so. This cooling process allows creosote and soot to form on these surfaces. They act as an insulator, and restrict the ability of the combustion chamber and heat exchanger. Benjamin's oval combustion chamber design allows the smoke to spiral and release it's heat cleanly and efficiently.

The oval design also eliminates the need for firebricks or wood grates. These were also found to reduce efficiency. Wood grates will allow too much combustion air to enter under your burning wood. Your wood will be consumed ineffectively and the heat will go up your chimney, instead of into your home. Firebrick, in essence, will do the same thing. BTUs and time will be lost as the unit is forced to heat the unneeded thermal mass.

Benjamin has a better idea.

Benjamin wants you to always keep a layer of coals and ash in the base of the wood burning combustion chamber. These are to be used in place of the conventional wood grates or firebrick. This will slow your wood burn down to a manageable level, allowing you to effectively remove heat from all three of the stages of combustion, and it will allow the smoke to do what it wants to do naturally.

OTHER POINTS:

Thoughtful design and construction.

1. The door to access the wood burning chamber is made out of cast iron. Benjamin is one of the few remaining wood burning manufacturers that still utilize a cast iron door. They do this because the cast iron will not flex the way a steel door will. This ensures a tight gasket seal and a reduction in lost BTUs due to a constant air leak draft.

2. The wood combustion chamber is located above the oil chamber. This makes it easier to load and clean. The wood shelf design further protects the oil burner from mishaps.

We are realists here. We know that someday (20 to 50 or more years from now with proper use), the wood combustion chamber will simply become "worn out". Isn't it nice to know that Benjamin has already planned ahead for you. Instead of going thru the cost of replacing the entire unit, they have made it possible for you to just switch out the combustion chambers and heat exchanger section. (ie. replace only the guts of the unit) This can save you thousands of dollars down the road when that time comes.

Another example of how Benjamin can provide comfort in more ways that one.

2) The FS140's Hand welded steel construction.

The one piece, hand welded design of the Benjamin FS140 combination fuel furnace is constructed of 3/16" and 1/4" thick steel. Benjamin's safeguards the FS140's consistently high degree of product quality, because each weld is individually inspected by the welder after it is created. The 3/16" steel thickness extends all of the way out to, and includes, the exhaust collar. Let's put it this way, the collar on the unit will probably be more rugged than the smoke stack it connects to. Because Benjamin uses thicker steel than many other manufacturers, they have been able to extend their product line's life span beyond that of which is expected.

Thanks to the revolutionary one piece design, the Benjamin FS140 is classified as a "single appliance". This enables it to be connected to a single solid fuel chimney flue, further reducing your installation costs. Maine code allows for this use, and insurance companies are agreeable to it as well.

To learn more about why Benjamin uses steel see the article "Steel Vs. Cast Iron"

3) The FS140's Innovative heat exchanger passage design.

Another innovation from Benjamin.

The wood and oil combustion chambers share a common heat exchanger, in a design that does not allow the wood smoke to ever come into contact with the oil burner. This ensures that there is never an oil firing failure due to wood soot build-up on the burner electrodes and nozzle. Now, you can truly utilize the convenience and reliability of oil heat.

As we mentioned before in our discussion regarding the combustion chamber, smoke likes to spiral by its very nature. Benjamin has extended the combustion chamber's unique oval shape into the heat exchanger as well. This design will reduce the amount of creosote and soot build up within the heat exchanger, increasing it's ability to work effectively, thus boosting efficiency.

The heat exchanger also features a gradual incline from the front to the rear of the unit. This allows for the natural rise of smoke. In an innovative and bold design move, Benjamin extended the heat exchanger into the return side of the system. This not only preheats the return air, but it also "scrubs" more usable BTUs from the combustion gasses before they pass into the chimney flue.

There are three cleanouts on the front of the unit, accessible after removing the front jacket cover (4 screws). To guard against the rusting and seizing of the heat exchanger cover removal nuts, Benjamin has opted to use dissimilar metals made of brass and steel.

A unique unit requires unique tools, and Benjamin has you covered. Each unit comes equipped with it's own custom designed and built steel clean-out rake!

4) How the FS140 operates.

The FS140 operates using two thermostats (or a single two stage programable thermostat) in your living space. One thermostat will operate the wood side of the system and one will run the oil. This means that you will be running two separate set-points.

Let's assume that you will be running primarily with wood, with oil backup.

The oil side of the system will be set at your "set-back" temperature. This is the temperature that you want the house maintained at when you aren't around, or when you go to bed at night. Let's call this temperature 58°F. (If you want to run the oil side as your primary heat source and only want to utilize the wood portion in emergencies, you simply use the oil thermostat much like you would any other while completely ignoring the wood thermostat)

Now, let's say that you want to fire up the wood heat portion of your furnace when you get home from work. Your house is being maintained at the 58°F oil set-point. You set the wood thermostat at your target room temperature. For now, we will call this 72°F. You go down to the basement and start your wood fire. (If you want to preheat the chimney to achieve a better draft for the wood fire, turn the oil thermostat up while you are loading the wood firebox.) Once you have a wood fire running that you are happy with, go back upstairs and go about your normal activities. The wood thermostat, set at 72°F, will maintain the house temperature by opening and closing the air draft control on the wood combustion chamber. (The silver box and chain connected to the top left corner on the front of the unit.)

When the wood fire goes out, the temperature of the house will start to drop. The wood thermostat will be calling for heat, but there is nothing on the other end to provide it. The temperature inside will continue to drop. When the house reaches 58°F (our oil set-back temperature) the unit will automatically switch over to the oil burner and maintain this set-point, until you reload and light another wood fire.

These set points are fully adjustable and can be set anywhere you want them to be. With the automatic switch over from wood to oil, you no longer need to worry about "rushing home to stoke the fire". The Benjamin will take care of everything for you. Go out with your friends, stay late at work, relax, and enjoy a slower pace to life. When you come home, the heat will still be on.

With a Benjamin in the basement, these are no longer concerns. You can remain toasty warm inside without the fear of frozen water lines, as both the FS140 combination fuel furnace, and the CC500 combination fuel boiler, when properly installed, can still operate effectively without power. They were designed to utilize gravity flow convection, if the need arises.