It is 8:50 on a crisp, sunny Atlanta morning. The outside temperatures are in the mid-40s. But inside Richard and Anita Seedorf's passive solar home it is 70 degrees F.
Mr. Seedorf points to an air-tight wood stove: ''That's the only source of heat we have beside the sun.'' The previous night he had burned two logs in the stove.
By contrast, in this reporter's nearby nonsolar home, in which the furnace had not been turned on and no fire had been built the night before, it was only 58 degrees around noon the same day.
Gavin Seedorf, their five-year-old son, bumps down the winding metal staircase in a sitting position. A few minutes later he runs out the door behind his mother - and breaks the No. 1 rule in passive solar homes: keep the doors shut tight.
Cold air coming in from the outside is the major cause of heat loss in homes, and is especially critical in sun-warmed homes, Gavin's father explains. Their front door is connected by a tiny entrance hallway to a second ''front door.'' This minimizes drafts. Special windows are hand-cranked shut to stop air leakage.
But some fresh air is needed, says Seedorf, an Atlanta architect who designs solar homes. Though his own home does not have it, his latest designs have a fresh air intake pipe that warms up some as it winds around a warm air outflow pipe.
The Seedorf's total heating costs last winter were about $70 - for three-quarters of a cord of wood. He estimates he saved about 70 percent off normal local heating costs for homes using natural gas.
The two-story, 2,100-square-foot house, built with some savings because of his involvement in the industry, cost $65,000. Seedorf estimates passive solar homes cost about $2 to $4 more per square foot than conventional homes. A North Carolina solar official puts the difference at $3 to $5 extra per square foot, which would be up to $10,500 additional for the Seedorf home.
The home here has large double-glazed glass windows on the south walls and part of the roof. Winter sun warmth is stored for night time release by the thick, tile-covered concrete floor in the dining room and 12 water-filled, fiber-glass columns along the family room windows on the south. The columns, eight feet high and 12 inches in diameter, each hold about 63 gallons of water, which fluctuates in temperature from 78 degrees in the day to 68 degrees by dawn.
Glass panels on one section of the roof warm metal strips. The paneled section opens into the home at both ends, drawing up cooler air at the bottom and releasing warmer air at the top of the vaulted ceiling.
All around the outside of the house, the earth is sloped upward to cover the 10 inch concrete walls to a height of about four feet. This acts as insulation.
But the house is not entirely solar. The family relies on an electric water heater - primarily, Seedorf explains - because he said he could not afford the cost of a solar water heater when he was having his home built. Now he says he wishes he had installed one because the cost can be paid back in savings in a few years.
During the summer, to keep the many windows from causing the home to overheat , he covers some of the rooftop windows with insulating panels and hand-cranks down shades over the vertical windows.