DO operational procedure.
The Benjamin DO line of ADD-ON boilers operate using one thermostat, but the unit itself requires a triple aquastat, and a single aquastat.
The oil side of the system will be set at your “set-back” temperature. This is the temperature that you want the boiler maintained at when you aren’t around, typically this will be a low limit of 150°F and a high limit of 170°F.
Now, let’s say that you want to fire up the wood heat portion of your boiler when you get home from work. 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 a wall thermostat up while you are loading the wood firebox. This will create a demand from the boiler and will fire the oil burner.) Once you have a wood fire running that you are happy with, go back upstairs and go about your normal activities. Your boiler was being maintained within the oil set-points, but the wood triple aquastat, set at a low limit of 170°F and a high limit of 190°F, has taken over and will maintain these boiler temperatures 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 boiler will start to drop. The wood aquastat will be calling for heat, but there is nothing on the other end to provide it. The temperature inside the boiler will continue to drop. When the boiler reaches the low limit oil set point of 150° the unit will automatically switch over to the oil burner and it will resume and maintain the oil aquastat set-points, 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 DO line, 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.