Letters to the Editor — March 2013
Praise from a plumbing industry newcomer
I am new to the service plumbing/drain cleaning industry after spending 30 years in the dental field. I have been very frustrated trying to find contractors who will share information with other contractors in the field. The health-care industry has countless study groups, organizations and publications that do just that. I have not found the “What is good for one could be good for all” mentality that I am accustomed to. That is, until I found Plumbing & Mechanical.
I have been very impressed with the content of PM’s articles and columns, and have learned more from reading just one issue than I have in four months of talking to people. Additionally, I was able to schedule a meeting with a company featured in one of your articles to talk about the pains and gains of computerization and going green.
I decided to go in a completely new direction with marketing since I dabbled in that when working in dental specialty practices and enjoyed building relationships with clients. Business is business, whether with a pipeline camera or an intra-oral camera. However, I am finding I have a lot to learn due to the unhindered advertising (fewer restrictive laws to juggle), increased competition with use of the Internet and the traditional view of “construction” workers.
I find that I have a different and fresh view of how to set ourselves apart from the others, even though I’m pretty sure my company thinks I am crazy. The articles in Plumbing & Mechanical totally support my efforts and allow me to simply hand the magazine over and save my breath. They also help me navigate the complicated aspects of advertising.
I want to say thank-you and that I look forward to future issues!
– Anne Boyle
Spartan Rooter Services
Clarifying barometric damper use to control boiler draft
I read Ray Wohlfarth’s January 2013 column (“Understanding barometric dampers”) with interest. I would like to take issue on several points.
The first being that barometric dampers are used on Category I flue systems. “It [diverter] is installed on boilers that use a Category I vent,” Wohlfarth wrote. Further along in the column, he stated: “Barometric dampers are only installed on boilers with negative venting. Boilers with pressurized vents would spill flue gases out of the barometric dampers into the room.”
First, let’s define Category I systems.
A Category I vent system is defined as “a noncondensing gas appliance that operates with a nonpositive vent pressure,”* also known in the field as a B vent system. Barometric controls also are used to control excessive draft on Category III systems. Category III is defined as “a noncondensing gas appliance that operates with a positive vent pressure.”*
In talking with stack manufacturers about the use of Cat I or B vent, they define positive vent pressure as anything above 0-in. water column. Cat I or B vent is not applicable on positive systems. B vent can only be used on 0-in. water column and negative pressure.
Barometric dampers are used on Cat I systems to control excessive draft. But they also are used on Cat III systems for the same reason. The same stack effect that occurs with a Cat I system can and will occur in a Cat III system. While boiler manufacturers argue over the need for draft controls with power burners, the fact is with a high chimney height, too much stack effect results in over-firing and burner flame liftoff.
As you lower the pressure in the combustion chamber from slightly positive to a negative pressure, the amount of gas increases. Like drinking with a straw — the harder you suck, the more negative pressure and the more fluid you get — the more negative the combustion chamber, the more gas you get. You end up over-firing the boiler. Stack temperature goes up and so do the gas bills. If the negative pressure gets too strong, the flame will come off the burner head, resulting in flame failure or even explosion.
I once consulted on a new project where lime was to be heated and dried in a duct with hot air from a power burner firing into the duct. Everything worked fine until they turned on the duct fans that sucked the lime up the duct into particulate filter bags. The duct pressure dropped to negative 8-in. or 10-in. water column and the burner flamed out. The engineering firm forgot to check the minimum combustion pressure for the burner. I could not find a burner that would fire into more than negative 5-in. w.c. The engineering firm is not around any more.
We assisted another contractor in the installation of a boiler replacement during the Christmas holidays a couple years ago. In 11 days we removed a cast-iron sectional boiler and replaced it with a new bent-tube boiler, water softener, condensate return makeup tank, blowdown tank and after-cooler. A problem developed during start-up. The positive stack venting system was installed up the existing chimney 48 ft. The draft pulled the flame off the burner during high fire. The contractor had not ordered a draft diverter because the manufacturer said the system did not need one. The manufacturer stuck with its story until we mentioned the 48 ft. of stack height. The proper solution was to install a barometric draft diverter.
In the last paragraph, Wohlfarth said, “Single-acting is traditionally used for oil-fired burners and double-acting is used for gas burners.”
Single-acting barometric diverters should be used on Cat III positive gas burners. I recently talked with a manufacturer’s tech support department. The response was consistent with a previous call I made years earlier: Power burners should use single-acting draft diverters, not double-acting as their literature suggests. Again, as I did before, I suggested that the manufacturer correct its website. When you have a power burner or positive stack pressure, you must use a single-acting diverter to prevent spill-out. In other words, do not remove the stops.
I hope this sheds some light on uses for barometric draft diverters.
* Sizing Handbook, Selkirk Metalbestos Nampa, Idaho #A99001, reprint 6/92.
– H. David West
Fort Worth, Texas
Ray Wohlfarth responds:
First of all, I would like to say how impressed I was with your state. I was recently in Dallas for the ASHRAE convention and the state was beautiful and the people were very friendly.
Second, thank-you for your feedback on my column. I appreciate the time you took to respond in such detail. It appears as if you have vast experience with boilers. One of the things I enjoy about this side of the industry is that it will always humble a person. Just when you think you know something, a job or building will challenge those beliefs.
We can both agree that barometric dampers can work well with Category I boilers with a tall stack. As far as Category III appliances, I would be hesitant to recommend installation of a barometric damper if the vent is positive and spillage of flue gases will occur into the boiler room and building. I have seen this installation done with dangerous results.
Conversely, I have seen barometric dampers successfully installed on Category III appliances when there is an induced draft fan on the chimney top or the flue. The damper would have to be installed on the inlet side of the induced fan, where the flue will not be positive. If this were the case, a single-acting barometric damper will work well. In my experience, these are rare and extreme care should be used when installing these types of systems. The customer would have to hire someone like yourself who has extensive experience with boilers and commercial venting of flue gases.