JIM AND Linda Viggiani didn't plan on becoming a living brochure on how to save energy. It just happened that way.

The Viggianis' conversion to the Efficiency Ethic started in Buffalo, N.Y., and reached critical mass in Rochester. Those were the years of the Big Snows, two and three years ago. In Rochester it came down one winter in great heaps, accumulating, they recall, to about four feet.

"It was the second week in April and we still had snow," says Jim Viggiani, shaking his head.

"It was up to the top of the picnic table," rues Linda.

"When our son [Jasen] was born, we had a chance to leave. So we did."

Here, Jim Viggiani, 43, directs instruction of emotionally disturbed children at the School for Contemporary Education in Springfield. Linda Viggiani, 37, is a substitute art teacher at the Godwin Middle School.

Their first shock in moving to Washington was the price of houses. The house in Rochester, which they had bought a few years earlier, had since doubled in price and they were able to sell it for more than $50,000. The Viggianis thought they had struck gold.

"We thought, 'Hey, we can take the money and get something really great,'" chirps Jim Viggiani.

They had alwasy enjoyed being just a few minutes from downtown. Here, However, they quickly learned they would have to forget about living close to the city. In their price range they found houses comparable to what they were used to only in the suburbs -- way, way out in the suburbs.

They finally settled on a $60,000 two-level, four-bedroom California-style house in a small, isolated development several miles outside Manassas.

Then came the second jolt.

In Rochester they had enjoyed relatively cheap electricity. "Our utility bill was only $10 a month," says Linda Viggiani. "We were really shocked when we cam down here."

The new house was heated by oil, and suddenly they were looking at a $550 bill for the season. Jim and Linda Viggiani got mad.

Jim Viggiani went out to Hechinger's and bought a heat reclaimer on sale for $90. Attached to the furnace flue, it captures heat that otherwise escapes with the exhaust.He vented it to a register above the boiler room door so that warm air blows into the downstairs recreation room and rises to the living room above.

He "derated" the furnace, making it more efficient by replacing the old burner nozzle with a smaller one.

At another Hechinger sale he paid $15 for a kit a to insulate the hot water tank. Then he went to an electrical supply store and spent $20 more on a timer that limits to five the number of hours the hot water heater is running each day.

Upstairs, he put in a set-back thermostat and lowered the house temperature to 56 degrees during the day and 62 in the mornings and evenings.

In 2-year-old Jasen's room he hung an electric radiant heating panel. In the master bedroom they turned on the electric blankets.

And for some months, they adjusted to living with less. They wore sweaters around the house and changed their schedules according to the hours the hot water heater was on.

"We've organized our lives around that timer," says Linda Viggiani, laughing. "If I do dishes in the morning, I'll wait till evening to do the wash."

And the Viggianis thought it was paying off. They thought they were at least keeping pace with the energy crisis when the telling blow hit.

Their first year here they had paid for oil at 50 cents a gallon. Last summer they watched fuel prices shoot through the roof and realized they weren't catching up at all: They were losing ground faster than you can say "Persian Gulf."

"When we saw the $800 estimated oil bill, we said, 'Geez, something's got to give.'"

Thus did the Viggianis become a solar family.

For many months Jim Viggiani had been collecting bits and pieces on solar energy: a magazine story here, a newspaper clip there. One day he found an ad for solar furnace plans by one Frank Maryl Jr. in Palmer, Mass. Viggiani sent away $7 or $8 for the plans, even though he could not tell you, then, how it was supposed to work.

"I knew the very simple concept of heat building up in a closed area, like in your car on a sunny day when the windows are rolled up. That much seemed logical."

The solar furnace is different from solar collectors you see on some rooftops. It is a long, triangular unit, like, half an "A," constructured on a concrete slab next to the house. It heats air rather than water, elminating the need for expensive copper pipes. The components are all standard building materials: Some kiln-dried 2-by-4 lumber, some wallboard, some concrete, a few hundred pounds of stone, caulking, plywood, glass, a couple of electric fans and paints.

Plus a few nails and about 90 hours of work.

The concrete is poured over a couple inches of gravel for drainage. It is covered by several inches of large stones that collect heat when the sun is shining and release it again at night. The back of the frame is made of 2-by-4s on 16-inch centers fitted with typical R-11 Fiberglass wall insulation.

The front of the collector, the hypotenuse of the triangle, faces south to gather infra-red radiation from the low inter sun. Corrugated aluminum sheets are laid over 2-by-4s and painted black to absorb to sun's rays. (The spans are alternately notched, top and botom, to create a zig-zag air flow inside the collector.) Glass is placed over the aluminum and sealed to trap the rays inside.

If Jim Viggiani were a carpenter or a solar engineer, his solar furnace would look much different. Because he is neither, let's just say the collector he built bears his own inimitable signature.

Much of the gravel for the slab he shoveled off his own flatroof. Many of the stones he used came from a neighbor's driveway. The wood sealing the back of the collector is old paneling a friend found at the local landfill.And when he went shopping , he always asked for damaged materials. The glass over the front of the collector is single-glaze in wood frame windows he picked up cheap at a lumber yard. And because he really didn't know what he was doing, and had to fit the side of the house, he cut the recipe in half, leaving him a collector 13 feet long and 7 feet wide, about 10 times too small to heat his entire 2,000 square-foot home.

The reflector, which bounces additional rays into the collector and is hinged to cover the glass during inclement weather, is hopelessly 8 inches short.

It might look awful and it might have cost only $500, but somehow, it works.

When the sun shines, the aluminum sheets absorb infra-red rays, warming the air inside to 80 degrees and more, even on the coldest days. When the temperature in the collector hits 68 degrees, a one-amp fan draws in air from the boiler room. When the air temperature rises to 72 degrees, a three-amp fan on the other end of the collector blows it back into the house.

"The other day when it was 30 degrees outside," says Linda Viggiani, "the oil furnace was off, the sun was shining and it was 70 degrees in here. I was wearing my sweater and I could feel it."

Jim Viggiani's collector is too small. It looks homemade. But since building it he has learned a lot more about what's wrong with it, and what he might have done, from a course at Northern Virginia Community College in Manassas. (The first time it was offered, he said, the course was canceled because he was the only one who signed up. He enrolled again recently and found 25 other adults in the class.)

He looks at their oil bills, then and now, and sees that last year they used 189 gallons of oil in January. This January they burned 136. For last year's season through February they used 518 gallons: This year it was 432.

Maybe it's been a mild winter. Maybe they've saved because of all the other improvements they've made on the house. In any case, says Jim Viggiani, "Our bedroom is right over the furnace and I can hear it click on. It's comfortable and it's exciting when it doesn't click on."