In some ways, unseasoned cedar makes a very good firewood. It is relatively lightweight, it splits easily and is easy to light, making it excellent kindling. It has a reputation, however, for emitting a large number of sparks as it burns and for burning too quickly.
Advantages and Disadvantages
Cedar burns hot but it does burn quickly, so its heat output per volume is lower than that of many other species. Red cedar produces 13 million BTUs per cord, and Eastern red cedar produces 18.2 million BTUs per cord. By comparison, white oak produces 29.1 BTUs per cord, white ash produces 24.2 BTUs, and beech produces 27.5 BTUs.
Because cedar has a relatively high moisture content in terms of both water and natural oils, it tends to spit and throw sparks when it burns more than many other species of wood, and the flying sparks can create a fire hazard.
Unseasoned cedar also burns cooler than cured wood, and when the fire is cooler, oils in the wood are more likely to escape unburned in the smoke and deposit inside the flue, which also presents a fire danger.
To reduce the amount of moisture in cedar, thereby decreasing its tendency to spark, cut the logs into 2-foot lengths and allow them to dry for at least nine months. Stack the wood in a sunny location, orient the wood so its cut ends face into the prevailing winds, and stack loosely enough so there is good air circulation between logs.
Burn cedar behind a closed fireplace door or screen to help contain sparks and reduce the risk that a flying ember will set something on fire. Have the flue inspected once a year to ensure there is no potentially dangerous build-up of creosote and soot inside it.
Combining cedar with a slower-burning species in the fireplace also cuts down on the concentration of oily wood being burned, reducing the problem of sparks and producing a longer-lasting fire.