Paul Painadathu allegedly made an attempt to commit suicide after fatally attacking his 74-year-old wife and 54-year-old son with a sharp edged iron bar at around 1am.
The octogenarian, a retired railway official, has been detained and an investigation has been initiated, police said.
Paul telephoned his other son, who is working in Qatar and informed him about the incident and told him that he was going to commit suicide. The panic-stricken son immediately telephoned their relative staying in the neighbourhood who alerted the police.
According to police, Paul had warned against excessive use of air conditioner due to an escalating electricity bill. But both his wife and son, who had recently undergone treatment for heart problem, ignored his advice and switched on the AC last night, police said.
Enraged over this, Paul entered the room in which the two were sleeping and hit them with the iron bar. Both died on the spot.
After the incident, Paul allegedly tried to kill himself by hanging from the roof but could not climb the ladder due to old age, police said.