This node covers the air ducting on an MGA, the flexible hoses and associated fittings that carry air between the heater matrix, the demister vents, and the fresh-air inlets. The MGA's heater system relies on a run of flexible hoses to carry warm air from the heater box to the two chrome-plated demister vents on the scuttle top above the facia, and a separate intake hose that draws fresh outside air into the heater matrix itself. Air ducting is among the most commonly damaged parts of a long-used heater system, the hoses crack, perish or tear at their clip positions, particularly where they route close to the exhaust manifold or around the engine bay.
Demist hoses, small and large
Two demist hoses are stocked to service the air distribution from the heater to the scuttle-top demister vents. The MGA Demist Hose (Small) is the smaller-diameter hose for either the shorter run or the branch feed to one of the vents. The MGA Demist Hose (Large) is the larger-diameter main run, typically from the heater outlet to the demister T-piece before the hose splits to feed both vents. The factory arrangement routes warm air from the heater through these hoses up behind the facia and into the underside of the chrome-plated scuttle vents, with air emerging in two streams directed at the inside face of the windscreen.
The hoses are MGA-specific in both diameter and flexibility specification, modern generic air hose is not a direct substitute as the fittings and routing are dimensioned for the MGA's factory installation.
Heater fresh-air intake hose
The Heater Intake Hose is the hose that draws outside air into the heater matrix. On pushrod MGAs the intake is routed from a fresh-air inlet on the left-hand side of the engine compartment to the heater blower, with the blower drawing fresh cool air through the matrix before it warms and passes through the demist hoses to the vents. On Twin Cam cars the intake is routed differently because the carburettors and air filters are on the right-hand side (leaving no space for the heater intake hose on that side), so the Twin Cam's hose is routed on an alternative path.
Hose adaptor and clips
A hose adaptor is stocked for joining two hoses or adapting between different end fittings in the duct run. Air hose clips (a general specification, different from the Supergrip water-hose clips stocked under the Heater Hoses node) are also stocked for securing the air ducting to their mating hose tails. Air hose clips need only be sufficient to keep the hose in place against the heater blower's modest air pressure; they are lower-specification than water-hose clips.
Carburettor intake hose
The Hose Carb Intake MGA is a separate item stocked here for completeness, an intake hose specified for the carburettor air-filter side of the engine installation. This is not part of the heater duct run and does not carry heated air; it is included under the Vents & Ducts node because of its related flexible-duct construction and fitment. Owners restoring the carburettor air filter installation should refer to the MGA Fuel > Carburettors section for the matching air-filter components.
Metal-strap tie wraps, period-correct hose fixings
A metal-strap-type tie wrap is stocked as a period-correct fixing for hoses and brake pipes. This is a stainless or zinc-plated metal band with a tab-and-loop fastening, used historically by BMC for securing brake pipes to the rear axle and for fresh-air hose fixing.
For cars being restored to factory specification, the metal-strap tie is the correct period fixing rather than modern plastic cable ties, which would be visibly out of period.
Mounting hardware
Mounting hardware is stocked for securing the heater and duct assembly: No. 10 (32 TPI) UNF recessed pan-head screws in 1" length, matching No. 10 zinc plain nuts and No. 10 locking spring washers.
Ordering considerations
Confirm the car's variant before ordering intake-side ducting, Twin Cam cars use a different intake routing than pushrod cars. For concours restoration, specify the metal-strap tie wraps for hose fixings rather than modern cable ties. Demist hose sizes (small and large) should match the existing installation; if in doubt, measure the outside diameter of the old hose at each run before ordering. The carb intake hose is a separate item and is only relevant if the carburettor intake ducting is being replaced at the same time.