A BEECH-95 TRAVEL AIR EQUIPPED WITH AN AUXILLIARY GAS HEATER EXPERIENCES AN UNCOMMANDED UNCOMFORTABLE RISE IN CABIN TEMPERATURE WITH SMOKE; EVEN THOUGH THE HEATER WAS NOT TURNED ON. THE PLT EXECUTED AN IMMEDIATE EMER LNDG.

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FINISHING UP AN ME CHK RIDE; THE TEMPERATURE IN THE ACFT BEGAN TO RISE; UNCOMFORTABLY SO. AFTER CHKING THE HEATER; WHICH WAS NOT OPERATING AT THE TIME; WE COULD NOT SURMISE THE REASON FOR THE TEMP RISE. SHORTLY THEREAFTER SMOKE BEGAN TO APPEAR IN THE CABIN. ALL SYSTEMS WERE CHKED AND NOTHING SEEMED OUT OF NORMAL RANGE. ZZZ APCH WAS CONTACTED AND ADVISED THAT WE WERE LNDG IMMEDIATELY. (AN EMERGENCY WAS NEVER DECLARED WITH APPROACH.) ZZZ1 WAS ELEVEN MILES AWAY; SO WE DECIDED FOR ZZZ2. THE FIELD WAS BASICALLY RIGHT BELOW US ON ZZZ3. THE HEAT WAS RISING AND THE SMOKE WAS GETTING WORSE AND WE MADE THE FIELD WITHIN FIVE MINUTES. AFTER LNDG AND GIVING CLOSE EXAMINATION TO THE HEATER LOCATED IN THE NOSE WHEEL WELL WE CONCLUDED THAT THE HEATER HAD MALFUNCTIONED. SIGNIFICANT BLACK SMOKE WAS LOCATED IN AND AROUND THE EXHAUST AND FWD LNDG GEAR DOOR.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE HEAT AND SMOKE WERE SIGNIFICANT AND HOT. HE WAS TOLD BY MAINT A FULL BLOWN FIRE WOULD HAVE ERUPTED IN THE NOSE COMPARTMENT HAD HE NOT LANDED THE ACFT AS QUICKLY AS HE DID. APPEARS THERE WERE TWO SAFETY SWITCHES THAT HAD FAILED. WHETHER THEY WERE THE OVERHEAT SWITCHES OR THE COMBUSTION PRESSURE SWITCH IS UNCLEAR AT THIS TIME. THIS WAS A JANITROL COMBUSTION TYPE CABIN HEATER. THIS ACFT IS A 1959 MODEL. HE DOES NOT KNOW IF THE HEATER IS THE ORIGINAL UNIT; A REBUILT OR UPGRADED MODEL. THE HEATER HAD NOT BEEN IN USE FOR AT LEAST 4-5 DAYS PREVIOUS AND WAS NOT OPERATING AT THAT TIME. WHATEVER INITIATED COMBUSTION IN THE HEATER WAS NOT COMMANDED BY HIM. RPTR ALSO STATED THERE WAS A LOT OF BLACK SOOT INSIDE THE NOSE WHEEL WELL AND ON THE EXTERNAL SIDE OF THE NOSE SECTION. THIS ACFT DOES NOT HAVE ANY OVERHEAT OR FIRE WARNING SYSTEMS ASSOCIATED WITH THE COMBUSTION HEATER.