The MGA heating and ventilation system is a genuinely period artefact, the heater was not standard equipment from factory but was offered as an optional extra, and was by some margin the most popular MGA option ordered. Cars supplied without the heater had a black cover plate fitted over the hole in the bulkhead shelf where the heater matrix would otherwise sit, and an optional cold-air ventilation kit was available as an alternative, allowing ducted outside air to the footwells without any heating capability at all. Even on heater-equipped cars, the system is modest by modern standards: a small heater matrix, a single fan speed, two round control knobs and a slide, and outlets only to the windscreen demister and the footwell.
Factory specification, Smiths F275 heater
The factory heater fitted to MGAs is the Smiths model F275, a 2.25 kW water-fed heater with integral fan. The heater unit is painted black and is mounted on the horizontal shelf behind the engine, the same shelf where the spare ignition key was screwed, under the factory specification. Two heater variants were fitted during MGA production. Pushrod cars (1500, 1600, 1600 Mk II) use Smiths heater unit FHR.2453/01, with the air intake hose routed on the left-hand side of the engine compartment.
Twin Cam uses Smiths heater unit FHR.2457/01. The Twin Cam has its carburettors and air filters on the right-hand side of the engine, leaving no space for the heater air intake hose on that side. The Twin Cam heater was therefore a different design with the intake re-routed to accommodate the engine layout. Twin Cam heater parts are not directly interchangeable with the pushrod-car heater.
The facia heater controls are on a small black add-on panel below the centre of the main facia, consisting of two round black knobs with concentric rings and a sliding knob marked "B" in the centre. The left-hand knob is marked "Push" above and "Air" below; the right-hand knob "Pull to increase" above and "Demist" below; the centre slide "Min Temperature Max". The sliding knob is pulled out to activate the blower fan.
Demister vents
Two chrome-plated demister vents are located on the scuttle top above the facia, carrying warm air from the heater to the inside face of the windscreen. On cars without the heater, the demister vents may be blanked or re-routed to the cold-air ventilation kit, depending on specification.
Heater water valve production change
At chassis 61160 (January 1959), the factory introduced an improved heater water valve design. Earlier cars had a less reliable valve arrangement that was superseded by this change. Owners restoring pre-61160 cars to functional use may find the improved later-specification valve the more practical fitment.
Cold-air ventilation kit, the non-heated alternative
For cars supplied without the heater, Smiths also offered a Cold Air Ventilation Kit, part number FHQ.6298/02 for pushrod cars or FHQ.6298/03 for Twin Cam, fitted as an alternative to the heater. This kit provided ducted cold outside air into the cockpit without any heating function, suited to export markets where heating was unnecessary. Cold-air-only cars are now rare, most owners having either retained a heater where one was factory-fitted or added an aftermarket heater to cars that originally came without.
Ordering by sub-category
This section is divided into three sub-categories covering all heater and ventilation service items. Heater System covers the heater matrix, blower fan, casing, mounting brackets and assembly hardware, everything inside the heater box itself. Heater Hoses, Valve & Controls covers the water plumbing, inlet and outlet hoses between engine and heater matrix, the heater water valve (including the improved post-61160 design), and the facia control knobs and cables. Vents & Ducts covers the air-handling side, demister vents on the scuttle top, air ducting from heater to vents, and the cold-air ventilation kit components where relevant.
Ordering considerations
Confirm the car's variant (pushrod or Twin Cam) before ordering heater components, the Twin Cam uses a different heater unit specification and some ducting components are not interchangeable. Confirm whether the car has the pre-61160 or post-61160 heater water valve if ordering valve parts.
Cars without a factory-specification heater can be retro-fitted with the appropriate Smiths F275 parts, though the installation is significant, re-routing of coolant, new control cables, and a heater-shaped hole in the bulkhead shelf are all required.