CONCORD, N.H. — New Hampshire — which last executed an inmate more than 70 years ago, by hanging — would likely carry out an execution in a prison gymnasium rather than construct a costly death chamber for its lone death row prisoner, Corrections Commissioner William Wren said Wednesday.

Addressing a symposium on the death penalty at the University of New Hampshire School of Law, Wren said he and his staff are ‘‘dusting off’’ execution protocols from the 1930s but the $1.8 million needed to build a lethal injection chamber is not in the cards in a state where inmates are so rarely condemned to death.