Six members of a family breathed their last due to suffocation following a gas leakage at their home in Mansehra on Wednesday, reported 24NewsHD TV channel.
A newly-born baby was also among the six victims.
According to the police, the dead were identified as Muhammad Afzal, his mother, wife and three children including the baby.
Police said the family forgot to switch off the heater before going to sleep last night.
Bodies have been shifted to King Abdullah Hospital for post-mortem.