Direct-vent oil boilers use a combustion mechanism that allows exhaust gases from burning oil to be vented directly outside without use of a chimney, unlike conventional boilers which do require chimneys. This results in more efficient fuel use and added safety for direct-vent oil boilers as compared to conventional boilers.
Direct-vent oil boilers use more efficient combustion mechanisms that extract most of the available energy from burning oil. In most cases, these mechanisms use a secondary combustion chamber to ensure more complete combustion. Because the boiler is not venting a large amount of hot fuel, the exhaust gases are much cooler than those produced by a conventional oil boiler and can be vented directly to the outside using a PVC pipe. Most designs use fans to help insure efficient exhaust of the combustion product gases.
Direct-vent oil boilers are more efficient for heating than conventional boilers, since they extract most of the heat from the fuel oil, making them more economical and ecologically friendly choices for heating. The most efficient direct-vent boilers use a sealed-combustion mechanism, meaning that they draw air for combustion from outside the structure where they are installed in addition to directly venting waste gases. These oil boilers can achieve average fuel use efficiency ratings of 85 percent, as opposed to the 65 percent rating typical of conventional oil boilers.