There will be no candlelit, Victorian Christmas at Washington's historic Heurich mansion this year: The elaborately carved furniture is covered with heavy plastic, and the colorful Persian carpets and velvet curtains are being cleaned. The library books are in boxes, and the 16 chandeliers are in pieces.

For the first time since the brownstone mansion was built in 1892 for Washington brewer Christian Heurich, the electrical, plumbing and heating systems, now inadequate, are being upgraded. The Columbia Historical Society, which owns the five-story, 30-room house, reluctantly closed the castle-like building for six months for repairs.

But updating the building, listed on the National Historic Register and one of the few remaining Victorian mansions in the Dupont Circle area, will be no small feat. In fact, as workers began the $1.5-million project they found many surprises in the house's structure that were unusual for homes of the period.

Michael Glynn, the supervising architect for the project, said no architectual drawings existed for the mansion. The work had to begin without the original drawings, believed to have been destroyed in a fire many years ago at the original Heurich brewery at nearby 20th and M streets NW.

It was a fear of fire that made Heurich insist that his home at 1307 New Hampshire Ave. NW be built as fireproof as possible. The result, as today's work crews have found, was a structure with electrical, plumbing and heating systems that would be difficult to modernize.

"This is a very advanced house for its time," said Perry Fisher, executive director of the nonprofit historical society. "We are discovering that he used masonry walls with almost no studs and the floors are concrete slabs supported by iron beams. And that all the wirings were clad in brass sleeves and then the concrete was poured over it. I don't know of another poured concrete house in Washington of this period."

Glynn said: "It is more typical of a commercial building than a residence. The poured concrete floors means he went first class because of the cost."

"It is impossible to do a project like this in the traditional way," Glynn said. "We don't know how we are doing the project until we start . . . . We're dealing with a virgin structure where nothing of substance has been done to it. It is hard for me to make the changes, to put the first holes in the walls. It hurts. I can't wait to start patching it."

Besides upgrading the wiring and plumbing, the historical society is changing the heating system from steam to electric and installing air conditioning in upper floors where the library and offices are. The main floor and kitchen will continue to be a museum.

Fisher, both fascinated and horrified by the exploration of the structure of the house, said, "We made a leap of faith that the elements will fall into place."

The mansion's interior is an extraordinary mixture of periods and tastes typical of the fashion of the 1880s -- the style Heurich selected. The combination of ornate plaster moldings, fanciful murals, paneled walls, intricately carved fireplaces, marble mosaic floors and gilt furniture challenge the viewer's ability to see it all at once.

Heurich and his family spent the winters at the Dupont Circle house and summers at their Hyattsville farm, now Prince George's Plaza. When Heurich died in 1945 at age 102, his brewery was still producing Old Georgetown and Senate beer.

When the Heurich family gave the house to the historical society in 1957, they also donated many furnishings on the main floor.

"Most house museums have already been so altered that this place is unique because so much of it is original," Miller said. "This is not our interpretation of the Heurich family--this is the Heurich family."

That the family did make some new purchases over the years became clear as furniture, chandeliers and carpets were moved out of the way of the workmen.

"We rolled up the carpet in the blue room and on the back it said 'offical carpet of the World's Fair,' " Fisher said. "They had bought it in 1939 and had it cut to fit the room. We had thought it was early 20th-century."

A big problem facing Fisher and Miller is what period the house will represent when the entire project is finished.

"We haven't made all the decisions on the presentation," Fisher said. "Due to continual residence, it is hard to pick a year. We now have the burden of knowing what everybody did to it."