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Fluepipe design, Part I


Feature Story

By George Lanthier


You might look at the title of this article and figure, ‘Oh boy, what’s this now!” Well, as it turns out, I’m learning that fluepipe design is not as easy as some people think it is. In fact, when it comes to the codes and good industry practice, many are doing it very wrong. As many of you know, I do expert witness work and I don’t like going against my industry, but wrong is wrong!

The codes are very specific in regards to oilburners. Remember that although your state may have its own code, the manual that came with the appliance probably says that you must also be in compliance with NFPA31, and when it comes to venting you must be in compliance with NFPA211. And then, there’s what works. We’re going to start with NFPA31 and end up with NFPA211.

There are three excerpts from NFPA31-2001 that we need to look at. They are:

3.3.6.3: Mechanical Draft-Type Burner. A burner that includes a power-driven fan, blower or other mechanism as the primary means of supplying air for combustion. This is also known as the same thing for my buddies in Massachusetts.
3.3.6.4: Natural Draft-Type Burner. A burner that depends primarily on the natural draft created in the chimney or venting system to induce the air required for combustion into the burner. Ditto on Mass.
6.5.1: An oil-burning appliance shall be placed so that the chimney connector is as short as practicable. This is the real point of this article. For natural-draft appliances, the horizontal length of a chimney connector shall not exceed 10 feet (3 meters) unless a draft fan is used. For appliances requiring a negative chimney draft, the chimney connector shall not be longer than 75 percent of the portion of the chimney above the chimney connector inlet. This is known as 527CMR4.04(9)(b)4 in Mass.

We don’t use natural-draft burners anymore. They are the old pot-and-sleeve-type burners and many of you younger techs have no idea what I’m talking about. Everything we use today is a mechanical-draft burner and has a fan in it, Beckett, Carlin, Heat-Wise, Riello, Wayne, etc. So you can throw NFPA31 3.3.6.4 and the draft inducer out the window for this discussion. But we have to take a good look at that 75-percent thing.

Essentially, I hate the term smokepipe. I’ve been doing my part to educate the industry to use the term fluepipe in front of retail customers since 1975. Why even paint a mental picture that oilheat is dirty in any way?

Keep in mind that in the codes and standards they don’t refer to them as either fluepipes or smokepipes, but rather as a ‘chimney connector.” Some of the other filthy street words that burnermen use are ‘blast tube” and ‘jet line” instead of air tube and nozzle line. I guess if you’ve never had a complaint about noise, then it doesn’t matter.

Another thing that sets me off are right-angled, 90-degree turns on fluepipe runs, and just wait until you see what I have to say about tees. The most dreaded tee is known in the field as a ‘plumber’s tee” and although many of you are sitting there gloating over that, be careful, it has its place. Regretfully, I’ve also seen so many put in by oilmen wrong that I would be a very wealthy man at just 50 cents a pop.

In Figure 1, I show the use of a ‘plumber’s tee” and when you go through most manuals you’ll see that although it’s correct for gas, it’s never been allowed 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 power burner it’s wrong. It has to do with Bernoulli’s Principle and Venturi’s and why jet tees, also known as mono-flo tees, work on hydronic systems.

I guess the best place to start is with an explanation of TEPL. TEPL is the Total Equivalent Pipe Length of a fluepipe. This chart is a brand new one that comes from Field Controls. It does a great job of explaining how to calculate it for the fittings used. Many thanks to Tim Begoske and John Cotton for getting me an advance copy on the day before Thanksgiving, thanks guys.

Let’s work a couple of examples. First of all, the traditional way. In Figure 2, we have a drawing that shows a simple install of an oil-fired appliance and we’ll set the fluepipe diameter at 6 inches.
We have three pieces that are 18 inches, 24 inches and 23 inches in length for a total 65 inches or about 5.5 feet, and then we add in for the two 90-degree elbows at 11 feet each for a grand total of 27.5 feet of TEPL.

In Figure 3, I have used two 45-degree elbows at 5 feet each and added them to my fluepipe run of 7 inches, 5 inches and 48 inches for a total 60 inches, or 5 feet. This gives me a grand total of 15 feet of TEPL, or roughly half of doing it the conventional way. Now comes the best part, the tee.
The bad news for those of you who love that ‘plumber’s tee” in Figure 1 is the dimensions are the same as Figure 2, but we remove one elbow and add the tee’s TEPL from the chart.

We now have pieces that are 18 inches, 24 inches and 23 inches in length that total 65 inches, or about 5.5 feet, and then we add in for one 90-degree elbow at 11 feet and a tee at 38 feet for a grand total of 54.5 feet of TEPL. Guess what? You may be in big trouble now. Remember that thing about ‘the chimney connector shall not be longer than 75 percent of the portion of the chimney above the chimney connector inlet?” Well, let’s see what happens with an atypical New England chimney of about 35-feet high.

With a 35-foot chimney we’re going to deduct 5 feet for the height of where the fluepipe goes into the chimney, leaving us an actual chimney height of 30 feet. Seventy-five percent of that leaves us a working dimension for a fluepipe of no more than 22.5 feet. So let’s look at fluepipe design.

Using the conventional way and using 90-degree elbows we ended up with a TEPL of 27.5 feet, or 5 feet more than what is allowed by the codes.

Using a plumber’s tee and one 90-degree elbow we ended up with a whopping 54.5 feet of TEPL or almost two-and-one-half times the allowed fluepipe size by code. Finally, there’s my way or the right way as far as the codes are concerned.

By using the 45-degree elbows, I ended up with 15 feet of TEPL, or about 65 percent of the code. By the way, are you finally starting to realize that you really didn’t know what you thought you did about Combustion and Oilburning Equipment, why it’s the title of my book on the subject and why you really need to take our seminar called ‘The North American Oil Burner Workshop?” Let me tell you, even in two days we don’t cover it all and that’s why the book comes with the course. OK, that takes care of NFPA31 for now on this subject, except for a few other things I need to put out to cover by own butt on this.

6.5.6 states essentially that you can’t have a fluepipe smaller than the appliance outlet.
6.5.8 states that you must pitch it at least one-half of an inch per foot of run
6.5.9 says watch the turns and keep the elbows to a minimum(sic) and of course;
6.5.10 says that you must properly support it and fasten all of the joints.

That’s the really short version and I truly suggest that you buy a copy and read it before we meet in court. You can get NFPA31 at www.nfpa.org, and for those of you in Massachusetts, you can get our CMR4.00 Guide from us at www.FiredragonEnt.com.

NFPA211 is all about chimneys, and as it turns out is used in all 50 states, including the Commonwealth of Massachusetts; sometimes a new wheel is just not needed. I honestly believe that every oil company service department should have a copy of this and every service technician and installer should be made to read it. All of my quotes are from the 2000 Edition, but they’re mirrored in the 2003 Edition, while the 2006 Edition is due out soon as well as NFPA31-2006.

Let’s first of all go over the duplicates that are carried over from NFPA31 to NFPA211. These are all done so I guess we get the message, right?

NFPA31 5.5.6 becomes NFPA211 9-4.2; NFPA31 6.5.8 becomes NFPA211 9-7.7; NFPA31 6.5.9 becomes NFPA211 9-7.8; and NFPA31 6.5.10 becomes NFPA 211 9-7.10.

In addition to that, NFPA31 6.5.1 comes back as NFPA211 9-3 and 9-3.1 and our NFPA31 definitions 3.3.6.3 and 3.3.6.4 are now defined in 3.3.36.1 and 3.3.36.2, so there, they got ya.

Last but not least is my favorite and the biggest problem of all for hacks in the industry. The problem is that this is one of those things in NFPA211 that even gets a lot of the good guys on a smoke, soot or fire insurance claim, Table 9.2.2.3, Metal Thickness for Galvanized Steel Pipe Connectors as shown in the next table.

This may come as a shock to many of you, but as you can see even the gauge of your fluepipe is called out. It’s one of the things stone-crushing insurance investigators go for when they don’t want to pay the claim and can’t find anything else to go to subrogation with. The trick is don’t let them; do it right, every time. Some of you may also think this is new; forget that excuse, this goes back to the 1970s. Don’t let wholesalers sell you their mistakes either. It is not OK to use what’s available. If it’s wrong, it’s wrong.

Now, put this article in a safe place because you’re going to need it for the next article we do on those Y-connectors.


See ya.


George Lanthier is the owner of the Firedragon Academy, a teaching, publishing and consulting firm. He is a proctor and trainer for the industry’s certification programs and is the author of nine books on oilheating and HVAC subjects. He can be reached at 132 Lowell Street, Arlington, MA, 02474-2756. His phone is (781) 646-2584; fax (781) 641-7099 and his Web site featuring the industry’s only ‘trade-only” discussion board can be found at www.FiredragonEnt.com.


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