The works from Althorp comprised a £1.62m, 757-lot attic sale, with a further £4m garnered from 78 lots of furnishings that were formerly at Spencer House, the family's London house, plus a further £12.6m from two Old Master paintings.
Sotheby's Chatsworth sale, which will take place on the premises over three days from October 5-7, will disperse over 20,000 objects in 1400 lots and is expected to fetch in the region of £2.5m.
Explaining the reasons for the sale, the Duke of Devonshire, who is deputy chairman of Sotheby's, said: "When we moved into Chatsworth several years ago, we found the attics filled with the contents of other family homes from generations past. With Sotheby's, we embarked on the lengthy process of selecting a group of items for sale that would allow us to create much-needed space in several rooms throughout the house."
As well as Chatsworth itself, those other family homes filling the attic spaces included Chiswick House, Hardwick Hall, Lismore Castle and the family's own London home, the now-demolished Devonshire House, which was designed and built by William Kent in the 1730s.
So along with the usual teacups, curtains and other surplus day-to-day effects of any large household, the sale will offer some substantial architectural fittings from a palatial London house by one of the best-known English architects.
Prime amongst them is a white marble chimneypiece designed c.1735 by Kent for the Devonshire House ballroom, which is estimated at £200,000-300,000.
By Anne Crane