We continue to receive many questions regarding our Model AFG burner and its ability to develop “high static pressure”.
This bulletin is intended to briefly explain the purpose of higher static pressure, the key operational components that develop it, and how the burner performance is seriously affected if these components are altered or removed.
The Need for Higher Static Pressure
High static pressure burners have been developed to function on high efficiency appliances and to overcome poor draft conditions. The blower in a high static pressure burner provides a “blast” of high pressure air on start-up to establish a stable flame, and enough pressure to push the products of combustion through the heat exchanger when the chimney draft alone is not sufficient. The high static pressure behind the flame retention head helps to resist and absorb any pulsations on start-up, shutdown, or during the running cycle.
The blower in some flame retention burners may not be capable of developing the static pressure required to establish a good flame and move the combustion by-products through the system. Usually the result is pulsations on start and stop, or an erratic flame throughout the run cycle.
This is not to say that these retention burners are outdated; however, where they are applied today may have some limitations.
Creating Higher Static Pressure from the AFG Burner
For sake of example, let’s compare our Model AF with the Model AFG. The key operational components within the AFG are the air guide which is black in color, resembles half of a funnel, and is factory installed within the burner’s housing.
The second component is the specially designed “smaller” blower wheel. The AFG blower wheel is physically smaller than the Model AF wheel but incorporates a larger quantity of fan blades. (See Figure 1.) The blower wheel is located at the optimum point on the motor shaft when installed. (See Figure 2.)
The air guide directs the air into the blower at the precise point to create an efficient pre-rotation of air, thus generating a higher static pressure when compared to the Model AF burner. The AFG blower wheel, even though smaller in size, will generate a higher static pressure and equivalent CFM (cubic feet per minute) of air than the Model AF when, and only when, combined with the air guide. The Model AFG burner has the ability of generating more than twice the static pressure of the Model AF.
One additional component in the air handling system is the motor. The preferred motor will have a closed-face end bell; however, if the open-face design is used, it must not have openings into the motor which extend beyond the circumference of the blower wheel once installed onto the motor shaft.
Removal or Alteration of AFG Components
The most common error made on the AFG air handling system, due to a lack of understanding, is in the removal of the air guide from the housing of the AFG. DO NOT REMOVE THE AIR GUIDE FROM THE BURNER. Once the air guide has been removed, the smaller fan wheel is rendered ineffective. You will experience an extremely poor and erratic combustion process, start to finish. Once removing the air guide, the static pressure of the burner drops by 65% even though the CFM of air output remains the same. The altered AFG burner is now operating well below the static pressure capabilities of the Model AF burner.
When removing and reinstalling the blower wheel from the AFG motor assembly, make sure it is positioned so that the distance between blower wheel back-plate and motor face-plate is 3/64″ ± 1/64″. (See Figure 2.) A larger distance than what is specified may contribute to loss of blower efficiency, increased blower wheel sound, or the wheel rubbing up against the air guide.
When replacing the motor assembly, utilize the specified motor incorporating a closed-face or small opening face-plate on the motor. This is to prevent a loss of static pressure into the motor assembly at burner start and during the run cycle.
You need to have an increased awareness of the need for higher static pressure operation from today’s burners. Altering the factory-installed components of a high static pressure burner can seriously affect the efficiency of the heating system and the performance of the burner.