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Case Studies
Pulse Furnace Lennox

The Lennox Pulse Furnace Is HVAC Heritage

Igniting tiny quantities of gas 60-70 times per second

Lennox is a longstanding HVAC company and in 1982 introduced its classic Lennox Pulse furnace. These high-efficiency 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. MTSI helped make the Lennox Pulse heater possible.

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.

Lennox Pulse Heater
Lennox Pulse Furnace Prototype

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

Not so with the Pulse.

Lennox Pulse Heater

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 heater 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.