The Evolution Of High Static Oil Burners
I glanced at them quickly, and then I refocused, trying to figure out what was missing.
“OK, Bill; I give up. Where are the chimneys?”
“That's the future, Jim. I drew it without chimneys. No need for chimneys in the future.”
At the time it was a bit of a stretch, but today … it's still a stretch for the capitol, though not for an oil-fired home. Oil burners have come a long way since my conversation with Bill. Chimneys are still the preferred venting option; however our new appliances and burners make them just that, an option.
Years ago, oil burners were designed to work in an appliance that had very little resistance to the flow of combustion gases. That resistance to flow is called draft loss - the movement of gases caused by draft.
Boiler and furnace designs were carried over from solid-fuel appliances, such as those that operated on coal or wood. Flue ways had to be large so combustion gases would vent by gravity. Controls were manual, with the operator responsible for the quality and intensity of the fire.
Stack temperatures, the temperature measured in the flue pipe, reached well over 600 degrees F, contributing to the quality of the chimney draft.
The biggest selling feature for oil conversion burners was “automatic comfort.” Now you could let the burner run the show. Energy costs were low, so thoughts of efficiency were outweighed by ease of operation. Turn on the switch, slide the thermostat to your comfort zone and enjoy the heat!
As we know, nothing stays the same. Soon energy conservation became a topic. The quickest fix for oil heat was draft control. A hand draft control (or damper) installed on solid-fuel appliances would increase efficiency by lengthening “burn times.” This was accomplished by slowing down the rate that the combustion gases escaped up the chimney.
The efficiency of the appliance increased by increasing the length of time that the heat contacted the heat exchanger. The longer the gases contacted the heat exchanger, the more time for energy exchange, hence the name “contact time.”
With an oil burner, a hand damper became impractical. Automatic comfort means there should be little or no need for user interaction. Hand dampers require someone to adjust it; that's hardly automatic. If the draft on the chimney is controlled, rather than the draft loss of the appliance, the same end was met.
That is where the weighted draft control came in. The weighted draft control allowed the burner technician to set up the system to an optimum level of operation, lowering stack temperatures. Now contact times could be lengthened through the heat exchangers so the energy went to the building rather than up the chimney.
As our industry grew out of its infancy, boilers and furnaces were specified for multiple fuel uses. Contact time and draft losses became an integral part of the appliance design.
Performance issues started to haunt older-styled burners, specifically not being able to overcome the system static pressures because of draft issues. Combustion gases couldn't exit the appliance properly, and soot was the direct result; an aspect of oil heat that people thought was “normal.” A properly specified, installed and maintained oil burner does not generate soot.
New & ImprovedThat brings us to today. Burners have evolved from lazy flames to the sharp, flame retention burners of today. Along the way there were some transition models that met the definition of flame retention, but wouldn't meet the design criteria of today's appliances.
Today's appliances are designed for efficient energy utilization through a combination of design characteristics, including the high contact time imposed on the combustion gases. That has driven the demand to overcome these static pressures either with an integral draft inducer or a power burner.
A high static burner is a burner that is capable of operating reliably and effectively against a resistance to the flow of combustion gases, or static pressures. This burner has been evolving in residential applications for the last 30+ years, although it has been available commercially for sometime.
The commercial burner offerings are a little easier to design because there is one main design criteria taken out of the equation - the homeowner! Static pressure is easy to overcome if you can push or pull air through the appliance; all you need to do is get a big enough fan and balance the flame without blowing it out.
Imagine this balance next time you strike a match. You are about to light a flame and blow hard enough to inflate a balloon without blowing out the match. The balloon is the flue passage; what has to happen? Get the flame big enough to overcome the wind and you've got it made; that's the balance a high static burner has to strike. Big fan, big flame, works for me!
But how much noise will that fan generate?
Picture that fan in a single-family ranch house. Think there may be a complaint? Trust me, there will be, and was. We had our share when the oil burner evolved to flame retention. But here is where the “new and improved” part comes in - today's high static burners are engineered to deliver performance while considering the customer.
As burners and appliances have evolved, stack temperatures have dropped. Oil stack temperatures that could mirror wood and coal stacks of 600+ degrees F are now replaced with boilers or furnaces that have net stack temperatures that are closer to 400 degrees F.
Remember that saying as a child, “Hot air rises”? Hot goes to cold, and the rate of movement is directly proportional to the temperature difference. Or, the greater the difference, the faster the movement. A chimney with a 600+-degree F stack temperature had a phenomenal draft! Drop the stack temperature by a couple hundred degrees or so and you have a lot of things happening. The easiest to see is a drop in draft quality. High static burners couldn't have come along soon enough.
Venting IssuesOne benefit that high static burners have created is the possibility for oil-fired installations without chimneys. This option is called direct vent. Direct vent devices are listed for that specific application, having flue collectors that are designed for that type of venting.
Do not try and apply direct vent accessories to nonlisted appliances. Remember that direct vent works on a balanced pressure design, meaning there is a specific ratio of combustion air and exhaust gas.
Some manufacturers will provide kits that combine the combustion air and exhaust hoods into one terminal, commonly referred to as concentric termination kits. In any case, a high static burner will be specified for these applications.
Rest assured that if you buy a new burner from any of our major North American oil burner manufacturers, you can consider it ready for the task at hand. Forget the past; new design burners are capable of maintaining a sharp, well-defined fire and exhausting combustion gases against high static pressure conditions.
There are two design changes that make this possible. One of the main changes is the oil burner motor design, specifically the use of a PSC motor. This motor design utilizes a capacitor for starting and bearings to maintain tight end play tolerances. The motor comes up to speed rapidly with lower energy demands on start than a typical split phase induction motor. Additionally, the motor operates cooler, allowing for a closed-end bell design that, in turn, contributes to the air control within the burner chassis.
The next design change concerns the air tubes and drawer assemblies. Manufacturers have all made different design changes, some to how the head positions are established, others to the head design and air handling characteristics. The design changes have strengthened the quality of the flame and, more importantly, they have improved the reliability of their respective products, especially under conditions that would be considered bordering on “pressure-fired.”
You've got it made with the new oil heat. Have a large hot water demand and no chimney or gas available? Try an oil-fired water heater that is side-wall vented. No wall space for direct vent? How about an out building for the boiler with underground PEX tubing into a heat exchanger in the basement? Even better, how about a self-contained boiler or furnace designed to be installed outside the building? There is even a combination boiler/oil tank available; just add electricity and water!
There are many options for your customers, from heating water to dropping high electric heat bills. With direct vent, the options are only limited by your imagination. With a new, high static oil-fired burner, it's all up to you!