One appliance most of us live with and take for granted is the heating and cooling system. It is within the last 30 years that high energy costs have motivated industry to increase the efficiency of these devices. However, here it is way past Y2K and many of us are still conditioning our homes with inefficient primitive antiquated technologies. It takes the force of government to push industry to produce more efficient HVAC.

High efficient heating technology is not as new as one might think. In 1982, I purchased a highly efficient gas furnace. It was called The Lennox Pulse.  This was a furnace like no other.  It was well over 90% efficient during a time when most people were lucky to get 55% efficiency from their open flame furnaces.

Compared to other furnaces, this thing was built like a piece of industrial equipment.  It was made of heavy gauge steel, and had an all stainless steel heat exchanger. 


Dyna Jet or pulsejet for RC models airplanes

The mechanism that created the heat was also very different as well.  It worked very much the same way as the small hobby Dyna-Jet Engine or pulsejet which is still used for RC model airplanes. 

The Dyna-Jet was made and patented in 1953 by a company called Curtis Automotive Devices.  The company was founded in 1947 in Dayton, Ohio by Russell R. Curtis and his father W.H. Curtis. Originally named Curtis Automotive Devices, they later changed ther name to Curtis Dyna Corporation. Today this company is known as Curtis Dyna-Fog, Ltd., makers of foggers. 

Russian inventor and artillery officer N. Teleshov patented a pulsejet engine in 1864 while Swedish inventor Martin Wiberg also has a claim to having invented the first pulsejet, in Sweden.  The first practical use of the pulsejet was the cruise missal like V-1 Flying Bomb employed by Hitler during WWII to carry a warhead to bomb Britten.  These became known as the Buzz Bomb.

A pulsejet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts and are capable of running statically, meaning they do not need to have air forced into its inlet by forward motion.


The pulse or combustion cycle of this engine is comprised of five phases: Induction, Fuel Injection, Ignition, Combustion, and Exhaust.

Starting with ignition within the combustion chamber, a high pressure is caused by the combustion of the fuel-air mixture. The pressurized gas from combustion is blocked by the one-way intake valve and so it exits via the rear through the exhaust tube which causes the engine to provide thrust, this force being used to propel an airplane forward. The inertia of the traveling exhaust gas causes a low pressure in the combustion chamber. This pressure is less than the inlet pressure upstream of the one-way valve pulling in air and fuel causing the cycle to begin again.  There is enough residual hot gasses remaining from the prior cycle to ignite the air fuel mixture just pulled in.  The spark plug is just to start the engine.

The Lennox Pulse worked very much the same way.  It too had a kind of valve that caused the forward only movement of the hot gasses through the heat exchangers.  However, the object of this system was to produce and capture heat rather than produce thrust.  There were resonators and chambers built in to reduce noise and funnel the heat through the primary and secondary heat exchangers.

This furnace was a marvel of heat transfer technology and it was calculated by my late father who was a chemical engineer to be a little over 95% efficient.  This furnace did save me over half off my gas usage for heating. This very well made furnace lasting nearly 20 years before it was replaced. Today the newer furnaces don't even last half as long, only about 6 to 10 years.

So, what happened to the Pulse? Well, this furnace was not without its issues. The main problem was that it was noisy. Even though there was considerable noise reduction within the unit, this beast required extensive sound deadening to be added to the installation thereby increasing its install price. This included duct sound insulation, exhaust and intake mufflers, and if it was to be installed on a wood floor, vibration absorbent rubber shock mounts. The next issue was that it was much more expensive than a conventional furnace of the time. It could be argued that it didnít really pay for itself in fuel cost savings. Then there was the sophistication of the setup of the unit itself.

In a high efficiency furnace that is going to extract as much heat as possible, there are certain engineering problems that must be overcome.  One of these is when the products of combustion are cooled below its 190 degree dew point, water with nitrogen oxides (NOx) condense on the heat exchanger.  Regular steel will quickly corrode causing immediate failure of the heat exchanger.  The Lennox Pulse used stainless steel in its construction to prevent corrosion.

Though some models of the Lennox Pulse were recalled, regardless how dangerous some might think they were, there are still quite a few of these in service today. 

Finally, because of certain sanctions on the importing of chromium, an ingredient used in making stainless steel, high efficiency furnaces are either made abroad or manufactured using a form of high temperature plastic coating on the steel heat exchanger.

Yes, there were complaints about the Lennox Pulse. But energy efficient or high recuperative gas furnaces was new technology that took a long time for other companies to catch up with. It took even longer for people to decide to have installed high efficient heating and cooling. This is because, like the American automotive companies, most HVAC industries realized there would be little to no demand for this product so they did not adopt these standards of technology until more recently.  Even then, most heating and cooling systems are still very much as they were in the early 1940s when forced air gas furnaces were first introduced.  The only difference is that mandates dictate that all new installs of gas furnaces be condensing high recuperative 90% or better.

Note.  As of this writing, ground source geothermal heating and cooling systems still cost over $20,000 to have installed.  Even with government subsidies, the payback is far beyond the cash purchase price of a system's typical lifespan of 12 years when compared to a standard system.

Steve II 2007