Joules married Mary Sparrow in 1930; they had three sons (one of whom died) and a daughter. He was a keen gardener and bird watcher, with a liking for John Clare, the poet and natural philosopher. In 1962 he took early retirement due to poor mental health and moved to Colchester, Essex; Joules had suffered from bipolar disorder since the second world war. He died on 25 January 1977 and was cremated at Colchester crematorium on 30 January 1977. On 24 April 1968 the Central Middlesex Hospital opened a residency, teaching laboratory and lecture theater, named Horace Joules Hall in his honour. A one-day conference on 'Progress in the prevention of chest disease in memory of Horace Joules' was also held at the Avery Jones Postgraduate Centre of the Central Middlesex Hospital, London, on 27 January 1978.
