The gunman was presumed dead in the ensuing blaze.
Attorney General Joseph Foster said late Monday night 48-year-old Stephen Arkell of Brentwood was shot to death when he answered the call in a suburban neighborhood for people older than 55.
After the shooting, the house burst into flames. A massive explosion blew the front off the house and within an hour, it was leveled.
Foster said Michael Nolan, 47, the son of the homeowner, is the suspected gunman. He is presumed dead.
Debra Vasapolli, director of public relations at Exeter Hospital, said that one person was taken to the hospital but said that person was not the victim of a gunshot wound.
Neighbor Wayne Hughes told the Portsmouth Herald that police responded to the house after neighbors heard an argument Monday afternoon and called 911. His wife, Susan, said that she saw a police officer arrive at the home and then heard "rapid gun fire."
She said she saw Walter Nolan, 86, being taken from the scene by ambulance before she was evacuated from the area. Public records indicate the house is owned by Nolan and he apparently lived in the home with his son.
After the blaze started around 4 p.m., firefighters were kept away from the scene.
Aerial coverage from WMUR-TV shows flames burning through the roof of the house and an explosion punching out the front of the house shortly after 5:30 p.m. Within minutes of the explosion, the house was engulfed in flames as black smoke billowed over the neighborhood.
After firefighters started attacking the blaze around 6 p.m., the fire was largely knocked down about a half hour later.