Friends of Back Bay’s Ayer Mansion were surprised last week to hear that the 395 Commonwealth Avenue home was listed for sale. The owner, catholic nonprofit Trimount Foundation, is asking $22.5 million.

The Mansion was built in 1899 and 1900, a collaboration between designer Louis Comfort Tiffany and architect Alfred J. Manning. Tiffany, a great popularizer of stained glass in home decor, designed the Mansion’s private chapel and its large colored windows, among other elements. The Mansion left the Ayer family estate in 1923, and was rented as doctors, dentists, and insurance offices for several decades.

The Association for Cultural Exchange, now the Trimount Foundation, bought the property in 1964. It continues to operate as a cultural center and residence for young women members of Opus Dei, a catholic group.

It has also been available to the public on a limited basis, allowing residents and visitors alike to enjoy the unique architecture and interior design. But the potential sale has thrown that into doubt.

“It’s really important to make sure this space is open to the public,” said Jeanne Pelletier, preservation advisor to the Campaign for the Ayer Mansion, which was organized to protect the property in 1998 after the drawing room ceiling fell in.

The Campaign has spent nearly $3 million, evenly divided between the interior and exterior, over the past quarter century. Work included restoration of the columns, front parlor, front hall, and the 20-foot long Tiffany stained glass window.

The Mansion also received a federal 2009 Save America’s Treasures grant, Community Preservation Act funds and support from the Warhol Foundation.

Pre Covid the Campaign hosted two or three tours a month with between ten and thirty people each. The Mansion also featured a music series with the New England Conservatory.

“The concern, of course, is that a single-family buyer would most likely close it,” Pelletier said, “Our first choice would be another nonprofit or an institution.”

The Mansion was added to the State Register for Historic Places in 1966 and was designated a National Historic Landmark in 2005. In 2013, the Trimount Foundation agreed with the city to preserve elements of the interior designs, according to a nonprofit registry of Back Bay houses.

“For the last 20 years it’s been a very exciting thing that Boston has somehow had, of all things to survive, this Tiffany house,” said Scott Steward, president of the Campaign for the Ayer Mansion.

The ornate but modestly sized Mansion has also played host to annual meetings and fundraisers.

“It was a fantastic party space for us,” said Heyward Parker James, founding board member of the Charlesgate Alliance. “We held two or three events there, but they were really amazingly successful.”

He agreed it would be a very fine thing if an academic or nonprofit institution bought the property and converted it to a permanent museum or cultural center.

James also suggested a student society might steward the property, as MIT’s Chi Phi fraternity did with the large corner home at 32 Hereford Street, though he acknowledged that might not be the most popular solution.

“We’re hopeful that the Mansion and its interior and exterior will be preserved,” said Elliot Laffer, chair of the Neighborhood Association of the Back Bay. “We’re hopeful that in the long run people will recognize the building for the treasure that it is.”

A buyer will have to conform to limitations on remodeling the exterior, Laffer said. The Ayer Mansion’s white stone face is the only surviving example of Tiffany’s exterior work.