Connecting more than one oil heating appliance to a common chimney can be easy and beneficial once we understand the basic guidelines. When following the guidelines for installation, the system will work for you. Disregard these guidelines, and the system can work against you.

The flue and chimney sizing not only controls the exhaust of combustion by-products, but also has a direct effect on the burner’s air supply. When the draft of the appliance rises, the fan wheel of the burner moves air easier. As the draft on the appliance drops, the fan wheel must work harder to move the same amount of air. Proper chimney and flue design, along with proper draft control, allow for an efficient combustion process. //

1. The chimney must be of adequate size to properly vent the gases created by the total BTU input of all appliances combined. Refer to Figure 1.
2. The flue piping of the system, whether for single or multiple appliances, should be as short a run as possible, and rise 1/4″ per running foot up and toward the chimney. Whenever possible, do not exceed 10 feet of flue pipe length.
3. Avoid using more than two 90-degree turns in the piping. Additional 90-degree turns further restrict the exhaust system on burner start-up.
4. The piping, when inserted into the chimney entrance, should not extend beyond the inside surface of the chimney liner. The area around the flue piping should be sealed where it enters the chimney.
5. When venting two appliances separately into a common chimney, always install the smaller flue pipe (appliance with lowest GPH input) at a higher point into the chimney than the larger flue pipe for the appliance with the largest GPH input. Refer to Figure 2.