§ 27.859 Heating systems. ( a ) *General.* For each heating system that involves the passage of cabin air over, or close to, the exhaust manifold, there must be means to prevent carbon monoxide from entering any cabin or pilot compartment.
( b ) *Heat exchangers.* Each heat exchanger must be— ( 1 ) Of suitable materials;
( 2 ) Adequately cooled under all conditions; and
( 3 ) Easily disassembled for inspection.
( c ) *Combustion heater fire protection.* Except for heaters which incorporate designs to prevent hazards in the event of fuel leakage in the heater fuel system, fire within the ventilating air passage, or any other heater malfunction, each heater zone must incorporate the fire protection features of the applicable requirements of §§ 27.1183, 27.1185, 27.1189, 27.1191, and be provided with— ( 1 ) Approved, quick-acting fire detectors in numbers and locations ensuring prompt detection of fire in the heater region.
( 2 ) Fire extinguisher systems that provide at least one adequate discharge to all areas of the heater region.
( 3 ) Complete drainage of each part of each zone to minimize the hazards resulting from failure or malfunction of any component containing flammable fluids. The drainage means must be— ( i ) Effective under conditions expected to prevail when drainage is needed; and
( ii ) Arranged so that no discharged fluid will cause an additional fire hazard.
( 4 ) Ventilation, arranged so that no discharged vapors will cause an additional fire hazard.
( d ) *Ventilating air ducts.* Each ventilating air duct passing through any heater region must be fireproof. ( 1 ) Unless isolation is provided by fireproof valves or by equally effective means, the ventilating air duct downstream of each heater must be fireproof for a distance great enough to ensure that any fire originating in the heater can be contained in the duct.
( 2 ) Each part of any ventilating duct passing through any region having a flammable fluid system must be so constructed or isolated from that system that the malfunctioning of any component of that system cannot introduce flammable fluids or vapors into the ventilating airstream.
( e ) *Combustion air ducts.* Each combustion air duct must be fireproof for a distance great enough to prevent damage from backfiring or reverse flame propagation. ( 1 ) No combustion air duct may connect with the ventilating airstream unless flames from backfires or reverse burning cannot enter the ventilating airstream under any operating condition, including reverse flow or malfunction of the heater or its associated components.
( 2 ) No combustion air duct may restrict the prompt relief of any backfire that, if so restricted, could cause heater failure.
( f ) *Heater control: General.* There must be means to prevent the hazardous accumulation of water or ice on or in any heater control component, control system tubing, or safety control.
( g ) *Heater safety controls.* For each combustion heater, safety control means must be provided as follows: ( 1 ) Means independent of the components provided for the normal continuous control of air temperature, airflow, and fuel flow must be provided for each heater to automatically shut off the ignition and fuel supply of that heater at a point remote from that heater when any of the following occurs: ( i ) The heat exchanger temperature exceeds safe limits.
( ii ) The ventilating air temperature exceeds safe limits.
( iii ) The combustion airflow becomes inadequate for safe operation.
( iv ) The ventilating airflow becomes inadequate for safe operation.
( 2 ) The means of complying with paragraph (g)(1) of this section for any individual heater must— ( i ) Be independent of components serving any other heater, the heat output of which is essential for safe operation; and
( ii ) Keep the heater off until restarted by the crew.
( 3 ) There must be means to warn the crew when any heater, the heat output of which is essential for safe operation, has been shut off by the automatic means prescribed in paragraph (g)(1) of this section.
( h ) *Air intakes.* Each combustion and ventilating air intake must be located so that no flammable fluids or vapors can enter the heater system— ( 1 ) During normal operation; or
( 2 ) As a result of the malfunction of any other component.
( i ) *Heater exhaust.* Each heater exhaust system must meet the requirements of §§ 27.1121 and 27.1123. ( 1 ) Each exhaust shroud must be sealed so that no flammable fluids or hazardous quantities of vapors can reach the exhaust system through joints.
( 2 ) No exhaust system may restrict the prompt relief of any backfire that, if so restricted, could cause heater failure.
( j ) *Heater fuel systems.* Each heater fuel system must meet the powerplant fuel system requirements affecting safe heater operation. Each heater fuel system component in the ventilating airstream must be protected by shrouds so that no leakage from those components can enter the ventilating airstream.
( k ) *Drains.* There must be means for safe drainage of any fuel that might accumulate in the combustion chamber or the heat exchanger. ( 1 ) Each part of any drain that operates at high temperatures must be protected in the same manner as heater exhausts.
( 2 ) Each drain must be protected against hazardous ice accumulation under any operating condition.
[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-23, 53 FR 34211, Sept. 2, 1988]