In Olbernhau (Erzgebirgskreis) a fire broke out in a former boiler house on Monday evening.
The owner had illegally restarted the building's old heating system, the police said.
He contracted smoke inhalation while trying to put out the fire and was taken to hospital.
The fire brigade's extinguishing work was finished quickly.
Olbernhau - How exactly the fire came about was initially unclear, as a police spokesman said on Tuesday morning.
It is being investigated for negligent arson.
dpa