WHITSETT -- Tom and Judith Bobo didn't know what to make of the new solar heating and cooling system Mike Sykes was preaching.

They just knew they wanted a log home out in the country, and Sykes had a knack for building them. So they listened as he described the system he had developed that uses heat from the sun and cool air from basements built in the ground to make homes comfortable year round.

He talked about an "envelope" around the house that allows air to circulate, bringing cool air in summer and warm air in winter. The Bobos, who then lived in Burlington, took it all in, figured it made sense, and decided to give it a try.

"It was a gamble. Like a lot of theories you have to prove it out," said Tom Bobo, who knows something about gambles after 30 years in the textile business. "In this case we had to build a house (to test it). I won't say we weren't a little skeptical. "There was nowhere we could go to look at one, and all we really had to go on was his say so that it would work."

That was the early 1990s. He and his wife moved into their 6,000 square foot home in eastern Guilford County in 1994. "We love it," Judith Bobo said of the house. Added Tom Bobo: "It works about like he said it would."

Theirs is one of 40 homes (note - as of 1999) that Sykes' company -- Enertia Building Systems -- has built all over the country using Sykes' patented solar energy design.

In September the American Wood Preservers Institute presented Enertia a national award for the home. The institute handed its Century's Most Innovative Wood Structure award to the company for the Bobos' house.

"I think ingenuity was the key word for this house," said Sarah Ely, communications manager for the wood preservers institute. "It utilizes natural materials in a unique way. They found a way of building a home and preserving resources."

Sykes, a Greensboro native and N.C. State mechanical engineering graduate, said homes using his design can be produced at costs comparable to conventional homes if they can be built in volume. Even with the current process of building them one at a time by hand, the cost is not much more than conventional, Sykes said.

For the Bobos' house, for example, the walls, with their stacked 6-inch-by-6-inch Southern yellow pine logs, cost about 20 percent more than the stud-and-dry wall walls of conventional homes. But since the house requires no heating, ventilation and air conditioning system, the Bobos saved part of that additional charge.

They also saved on labor, Sykes said, because stacked log walls take less time to install than dry wall. And the energy savings over the years makes the house a real winner, he said. His company estimates that, compared to conventional homes, his homes save up to $100,000 in energy costs over 30 years.

Equally as important, he says, they reduce dependence on polluting coal and fossil fuels for electricity generation. "I feel it (his business) is a niche right now," said Sykes, an environmentalist and member of the Sierra Club. "But it's got to become mainstream or we're all cooked."

The idea for his design comes from his study of heat pumps in college. A heat pump heats and cools by absorbing the heat and cooling from the air, water, ground or other materials around it. During the early 1980s Sykes began wondering why homes couldn't do the same thing.

"It was a light bulb thing," he recalled. "This house doesn't need a heat pump. It is one. That's what houses are, wooden heat pumps." It took some out-of-the-box thinking and some testing and retesting. But he finally came up with a design that works, he said.

Instead of the usual "static" solar design that relies on bringing sun light in and relying on insulation to capture it, he came up with a "dynamic" design. It exploits the tendency of hot air to rise and cool air to fall to create a circulation that keeps the home's temperature comfortable.

Sykes made up a name for this process -- enertia -- and he figure out all the mathematics. Now he and enertia, which he made his company's name, have found their way into college thermal dynamics textbooks. "I look up my name in the index," he said with a grin.

Sykes' design calls for a 7-1/2-inch "envelope" on the north facing wall. The envelope is an open space between the outside and inside walls that goes from the basement to the attic and allows an unimpeded flow of air.

A sun room on the south facing wall doubles as part of the envelope. It captures heat from the sun, which rises through vents in the ceiling into the attic. In the summer, part of that heat is vented through attic windows and the air circulates down through the basement where it is cooled and sent back through the house.

In the winter, the warm air is circulated from the attic down along the north wall to the basement where it warms the air and sends it back through the house. The temperature differential between the north wall and the south wall determines the direction and speed of the air flow. Since the south facing wall in the northern hemisphere is always the warmest, the air flows from the south wall, through the attic, down the north wall, through the basement and back again. "The operation," said Sykes, "is incredibly simple."

His design takes advantage of the fact that the temperature of the earth is a constant 53 degrees nine feet below the surface. So basements built at that depth have a constant temperature.

While conventional houses are trying to cool outside temperatures that can rise to 100 degrees or heat outside temperature that can drop to 10 degrees or lower, his homes won't drop below basement level temperature and seldom rise above 80 degrees. "People who like to keep their air conditioning at 68 degrees in the summer probably won't like this, but we do," said Judith Bobo, a Burlington marriage and family counselor. "It's just, where's your comfort level?"

The home must have solid walls for the system to work. Only solid walls, he said, can both insulate the house and absorb an adequate amount of heating or cooling. But not just any solid walls will work. Southern yellow pine offers the right balance between insulation and density for the system, Sykes said. But aerated concrete and some gypsum products will also work, he said. The system won't work with the stud and dry wall walls found in most American homes, he said.

Solar collectors on the roof supply the hot water heater and circulate through pipes in the floors so that the floors are always warm during the winter.

One thing his system hasn't been able to tackle is humidity. But Sykes says he's working on that. He has ideas on processes for absorbing humidity during the day and releasing it at night.

Sykes has found plenty of demand for his design. He has a nine home, $1 million backlog and he hasn't even advertised.

Lots of customers have found him through his site on the Worldwide Web -- www.enertia.com. One night recently that site got 3,100 visits. And during 1998 every home purchased came over the Internet. "The Internet has made this business," Sykes said. "We've gone from a local company to a national company just because of the Web."

Working through that backlog could take more than a year. To speed up production he is currently trying to raise $350,000 for a special German woodcutting machine. It will allow his company to cut in one day the volume of logs it now takes him a month to cut by hand.

"I make no joke about it, we need money," Sykes said. "We need investors (in order) to buy these machines and hire people to run them. The orders are there." He figures most Americans would prefer a workable solar design if they had a choice -- one that saved them money and was friendly to the environment.

The Bobos like that, too. But that wasn't the main reason they opted for Sykes' design. "We did it for the self sufficiency aspect of it," Tom Bobo said. "We could be comfortable out here regardless of the weather."