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Case Studies

The Pulse Is a Piece of HVAC Heritage

Igniting tiny quantities of gas 60-70 times per second

Lennox is a longstanding HVAC company and in 1982 introduced its classic Pulse high-efficiency furnace. These units are known for their distinctive “pulsating” sound, which is produced when running, which sounds somewhat like a small internal combustion engine when heard from an exhaust termination on the outside of a building.

The Pulse used a unique design that led the way in natural gas heating technology. For one, it included a cast iron combustion chamber complete with a spark plug, a resonator and expansion chamber, and finally a heat exchanger. 

Lennox was the first company to use this new technology.

Other furnaces at the time also struggled to send more than half of their heat into a home. 

Not so with the Pulse.

This energy-efficient furnace could extract more than 90 percent of health energy from combustion of propane or natural gas. The furnace uses two heat exchangers and low-temperature PVC for the exhaust, the use of a fan and a condensation line to dispose of runoff produced when extracting heat from the combusted gas.

The device also ignites tiny quantities of gas 60-70 times per second, with complete combustion occurring with each “pulse” ignition, delivering almost waste-free heat.

This Lennox Pulse furnace controller is serial number no. 11. We were tasked with writing code for its very low-cost microprocessor that used only 4 bits X 1k nibbles, or 512 Bytes to control it.