The victim’s body was found after officers were called to reports of an explosion in the early hours of Sunday on Farrow Road, Spalding.
Lincolnshire police said the property in Farrow Road suffered “100 per cent damage”.
A second man is receiving treatment after he suffered burns while trying to help as he passed by the fire.
The man in his 50s was pronounced dead at the scene despite the efforts of emergency services and members of the public.
Police are now investigating the cause of the fire, but they are said they are “keeping an open mind” and encouraged the public not to engage in speculation.
A police spokesman said: “The cause of the fire is under investigation, and we are keeping an open mind as experts from Lincolnshire Fire and Rescue Service investigate today.
“We would encourage people not to speculate while we investigate the cause.
“Officers will remain in the area for the next few days carrying out inquiries.”
Police are asking anyone who saw or heard anything, or who captured the incident on doorbell camera or dashcam, to get in touch by calling 101 quoting incident number 43 of 7 August.
You can email: email@example.com incident number 43 of 7 August in the subject line.
If you wish to remain anonymous, you can call CrimeStoppers on 0800 555 111 or you can give information anonymously online