Draft Controllers

In between my other office duties and writing articles and books I spend way too much time surfing the Internet. Although the Internet is a great place to find a lot of information, some of it is good and some of it is bad since much of it is sadly based on opinions and urban legends and not enough on essentials. You can find a discussion board on my site at DragonTalk, which is located at FiredragonEnt.com. Here’s my take on an Internet discussion about draft regulators. It was about how draft regulators are supposed to work and where they belong.

There have been millions of words written on this subject of which I’ve written thousands and yet I see the same old mistakes being made day after day. The following is an excerpt from my book Advanced Residential Oilburners that can be purchased on my Web site. This is one of the most common mistakes made by many in our industry and why things don’t always work the way they are supposed to.

“With much of the new equipment today, draft regulators, Figure 1, are a device that may no longer be necessary, but don’t forget about them when high draft is encountered, and always make sure you comply with the code. Make sure that they are installed between the turns in flue pipes to reduce turbulence, and to assure better operation. Under perfect conditions they would be installed 18 inches from any elbow or tee, but do the best you can. I know you really won’t do this, but you should never install a regulator into a manufactured tee. It should be mounted into the collar that comes with the regulator, or a device called a regulator tee. When a regulator tee, Figure 2, is compared to a regular tee you will see that the branch is closer to the pipe run than usual. This is the method that should always be used to ensure the regulator works properly. It is very important that the length of the pipe from the regulator opening, into the ambient room air, be correct to control the flow of flue gas present in the flue pipe. There really is not a lot of time involved in cutting in a collar, and the regulator will work as designed and properly control the draft in the flues. The really important question is; when were you ever taught (correctly) to put a draft regulator in a tee? The bottom line is read some of the literature that comes with these products you work on and install.”

This is taken from one such manufacturer’s manual:

“It is advisable that a draft regulator be 10% larger than the stack pipe diameter to ensure the best control of draft. The draft control should be installed in the stack between the appliance and the chimney. The draft regulator can be installed at a greater distance beyond the appliance if necessary or in the chimney. The draft regulator is designed to operate properly when the hot combustion products are flowing in right angles to the draft control. It must be mounted so it is level. It should be installed in the collar supplied by the manufacturer and not be installed in a preformed tee since the throat of most tees is too long.”        

Never install a draft regulator in a ‘plumber’s tee” either. Here’s another excerpt from my book.

“Figure 3 shows the use of a ‘plumber’s tee’ and when you go through most manuals you’ll see that although it’s correct for atmospheric gas, it’s never been recommended for oil. In fact, it’s even wrong on many gas jobs today. The trick again is whether the burner is mechanical draft or natural draft. With natural draft, like atmospheric gas, it’s right. With any powerburner, it’s wrong. It has to do with Bernoulli’s Principle and venturis and Y or jet tees also known as mono-flo tees found on hydronic systems.”

Finally, another point to keep in mind is that a draft regulator should not be used to control large amounts of excess draft, but only as a ‘fine tuner.” If you have excess amounts of draft you need to do one of two things: add one or more additional regulators or install a neutral pressure point adjuster, as discussed in my book.

If you have an excess draft situation, try this old and simple trick: install a neutral pressure point adjuster; see Figure 4. The adjuster is a device that will reduce excessive draft and draft regulator flow. It is especially helpful with powered draft devices and excessive chimney draft situations. Both situations can cause flame problems, condensation and chimney connector damage.

·         Start by cutting a piece of sheet metal as shown in C to form the adjuster slide piece.

·         In drawing A, start by making a cut about one-third diameter through the flue pipe.

·         Insert the adjuster into the flue pipe, start the burner and set breeching draft for -.02 inches W.C. or to the specific manufacturer’s recommendations.

·         When adjustment is complete, scribe the adjuster with a line around pipe B.

·         Make a second line about one inch above the pipe radius line.

·         Trim off the excess stock as shown in C, and then slit the stock between the lines vertically. Bend the segments in alternate directions.

·         Replace the adjuster, start the burner and verify settings taken earlier.

·         If unchanged, bend the tabs against the flue pipe, drawing D and anchor in place with sheet metal screws, or even better, pop-rivets. Seal any joints with silicone and the adjuster is completed.

The adjuster will reduce the velocity and strength of the draft currents and allow you to make a permanent and safe adjustment that cannot be adjusted again. The adjuster has been used for many years and has had great success on both oil and gas applications.

NOTE: Before locking the adjuster in its final position, make sure that the final firing rate has been set, and that all draft settings have been made and are final. Finally, before securing the flue pipe in place, as per code, with screws, rotate the pipe 180-degrees. This is done so that when the adjuster rots out it falls to the bottom of the pipe rather than potentially blocking it.

By the way, another great trick is before you do anything else try putting on a draft regulator that’s one or two sizes larger. If you used the collar that came with the regulator instead of a fitted elbow, it could be the simplest cure and now you know another reason for not using a manufactured tee.

See ya.

*George Lanthier is the owner of Firedragon Enterprises, a teaching, publishing and consulting firm. He can be reached at Firedagon Academy, 608 Moose Hill Rd., Leicester, MA. His Web site is www.FiredragonEnt.com and his phone number is 508-421-3490.