What is an ignition transformer?
An ignition transformer is a step-up transformer used in oil and gas burners to generate the high-voltage spark required to ignite the fuel-air mixture. It takes standard line voltage (120V or 240V primary) and steps it up to a much higher secondary voltage — typically 6,000V for gas burners or 10,000V for oil burners — which arcs across the ignition electrodes to create the ignition spark. Used on commercial boilers, residential oil furnaces, industrial process burners, and gas-fired heating equipment.
What is the difference between a 6,000V and 10,000V ignition transformer?
The secondary voltage is matched to the fuel type. Gas burners typically use 6,000V secondary transformers (Allanson 1092 series, Dongan A06-SA6) because the gas-air mixture ignites more easily and does not require as high a voltage as oil. Oil burners require 10,000V secondary transformers (Allanson 2721 series, 421-BT series) because atomized oil-air requires a higher energy arc for reliable ignition. Using the wrong secondary voltage can result in ignition failure or transformer damage.
What Allanson transformer fits a Beckett AFG oil burner?
The Allanson 2721-628G is the correct ignition transformer for Beckett A, AF, and AFG oil burners. It has a 120V primary, 10,000V secondary, 23 mA, 250 VA, mid-point ground, and includes a replacement gasket (the "G" suffix indicates gasket included). The 2721-628G is the replacement for the obsolete 2721-628A. Note: it is not compatible with Beckett NX burners.
What is the Allanson 421-BT636 used for?
The 421-BT636 is a universal replacement ignition transformer — 120V primary, 10,000V secondary, 250 VA — used when the original brand-specific transformer is unavailable. It cross-references against France LAUV, Webster 312-25AX0600, Dongan LJH-90, and Sid Harvey T1-15. It includes a mounting base. The 444-BT636 is the 240V primary version of the same transformer.
How do I find the right ignition transformer for my burner?
You need three pieces of information: (1) burner manufacturer and model, (2) primary voltage (120V or 240V from the nameplate), (3) fuel type (oil or gas). We cross-reference against France, Webster, Dongan, Sid Harvey, and Allanson part numbers. Call us at (901) 458-2000 or contact us with your burner make and model and we'll identify the correct transformer.
What is the Resideo AT140A1000 and how is it different from an ignition transformer?
The Resideo (Honeywell) AT140A1000 is a 24V HVAC control transformer — completely different from Allanson and Dongan ignition transformers. It steps 120V primary down to 24V secondary at 40VA to power 24V control circuits: thermostats, gas valves, zone valves, and control relays. It mounts four ways (foot, plate on 2×4" or 4×4" outlet box, clamp, or panel) with color-coded 9" leadwires on primary and two screw terminals on secondary. Meets NEC Class 2 and UL 1585. The AT72D1006 is the plate-mount-only variant. These are control power transformers — they do not produce a high-voltage ignition spark.
