The man and woman were found late Tuesday after the hotel's owners alerted police that the tourists were not responding to calls, police official Umesh Raj Joshi said.
Police officers broke the windows, which were taped shut, and found the bodies lying on the bed.
Joshi said they appeared to be regular visitors to Nepal and the bodies were taken for autopsy. An investigation is underway, and Italian officials have been notified.
Gas and kerosene heaters are commonly used in Nepal during the winter because of shortage of electricity. These heaters are dangerous if used in closed rooms and can cause suffocation and poisoning.
Nepal gets about half a million tourists every year and they are a major source of foreign currency.