FIREWOOD : Hot Commodity : It’s abundant, relatively low-priced and going up in smoke.

While the recent onslaught of Arctic air has wreaked financial havoc on many of Ventura County’s 1990 crops, it has been a windfall for those who depend on cold weather to generate sales of a commodity that keeps us all warm.

It’s simple. No scientific prognostication is needed to determine firewood sales. If it’s cold, business is brisk.

And right now it’s on fire.

Ventura County residents are fortunate in that firewood, for now, is abundant and priced substantially lower than in other parts of Southern California.

Increased competition--as the number of salespeople entering the business grows--also helps keep the price of firewood in this county at a moderate level.

In the market for some firewood to provide that extra heat and coziness? There are a few things you should know before purchasing:

* Firewood is sold by the cord--a measurement of 8 feet in length, 4 feet in height and 4 feet in width. Most firewood vendors also offer half cords (4 by 4 by 4) and even quarter cords.

* If you intend to use the wood this winter, make sure you purchase firewood that has been seasoned for at least six months and preferably up to two years. The bark of adequately seasoned wood should fall off easily when dropped. Firewood not given ample time to dry out will be difficult to light and, once lighted, won’t keep burning. Wood that has been sitting longer than two years will be prone to rotting and bug infestation.

* The three main varieties of firewood available from Ventura County dealers are oak, eucalyptus and avocado. Judge carefully--not all are alike. The most popular, and most expensive, is oak. A hardwood, oak is the longest and hottest burning of the three. Eucalyptus, an oily hardwood, burns long and hot, but not everyone likes the aroma. Avocado is by far the cheapest of the three and burns hot. However, you’ll use more because it doesn’t last long.

Although you’ll want to shop around, on the average oak will run you $200 a cord, eucalyptus $160 and avocado $110. These prices also include delivery, but you’ll have to stack it.

For a firewood vendor in your area, check the phone book. The yellow pages will list some of them under “Firewood,” or check the classified ads.

A lot of the firewood being sold is from tree removal businesses, such as West Coast Tree Service in Ojai.

When people have trees taken out, owner Jerry Kenton said, “Are you going to take it to the dump or sell it for firewood?”

Considering the work involved, he said, it’s not a choice easily made.

“You’ve got to cut the tree down, cut it up, load it on the truck, unload the truck, split the wood, advertise, load it up again and then unload it at the buyer’s home.”

Does Kenton have a firewood preference?

“Eucalyptus is your best buy, I feel,” he said. “It hardly leaves any ash, whereas oak tends to leave a lot of ash. Plus, the oak doesn’t stack as tight as eucalyptus. You get more wood in the cord when you’re able to stack it more tightly.”

Eucalyptus stacks tighter because of its round, straight trunk and branches, while oak is much more contorted.

Kenton said oak will burn hotter than eucalyptus, “but in a regular fireplace, you’ll lose up to 90% of the heat up the chimney anyway.”

For most firewood dealers, oak is always their best seller.

“We sell more oak year in and year out,” said Sydney Kane, manager of Hilltop Feed & Ranch Store in Thousand Oaks, which also offers eucalyptus. “People are just more familiar with oak,” she said, “because that’s what the neighbors are burning.”

And if you’re burning a lot of firewood--Kane said the average family burns half a cord during the winter--there’s something else to keep in mind: creosote.

“Creosote is a tar-like substance that builds up on the walls of the chimney,” Jean Canada said. She and her husband own Chimney Sweep in Ventura. “It’s important to have it removed because it’s highly combustible and can catch fire when left to build up,” she said. Scouring with a long pole attached to a wire brush, creosote is removed and collected via vacuum. “Depending on how much and what kind of wood you burn,” Canada said, “you should have the chimney cleaned every two years.” One of the worst creosote culprits, she said, is the long-burning processed log that is paper-wrapped and lights easily. She also suggested, as a safety precaution, placing a spark arrester on the top of the chimney. “It’s just a small metal screen cage that keeps sparks from jumping onto the roof and your neighbor’s roof.”

If firewood vendor Kenton’s business is any indication, there are a lot of sparks jumping, now that cold air has come to Ventura County.

“My phone is ringing off the hook,” he said. “It always does once those gas bills reach $200 or more.”