An attempt to steal copper from the Firefighters Hall and Museum of Minneapolis has resulted in a financial blow to the nonprofit museum.

Sometime in the past three weeks, thieves damaged its rooftop air and heating units, apparently in an attempt to steal copper contained in the machinery.

James Sandberg, chairman of the museum's board, estimated Sunday that the loss from the theft is about $13,000, the cost of replacing the two units at 664 22nd Av. NE.

The damage was discovered earlier this month when a worker went on the roof to check for possible ice damage.

Sandberg said the thieves climbed onto the roof of the one-story building, tore open the cabinets surrounding the heating and cooling units, then cut out the condensers.

"For a nonprofit, this really hurts," Sandberg said.

The museum, which is open only on Saturdays, has been in operation for about five years.

Sandberg said Minneapolis police investigators told him that copper theft is not uncommon these days.

Most of the replacement cost will be paid by insurance, but the museum will have to pay the deductible and also the depreciation because the units are two years old.