Gas Pipe Sizing Takes Planning

HOW MUCH WILL you charge me to install a gas log set? Dont you just love conversations that start off like that? Theres only one easy answer: It depends. The salesperson who handled the sale told the customers that installation was a snap, so theyre not normally ready to hear or want to understand all that goes into proper calculations regarding gas line sizing requirements. Thats our job having the

HOW MUCH WILL you charge me to install a gas log set?” Don’t you just love conversations that start off like that?

There’s only one easy answer: “It depends.” The salesperson who handled the sale told the customers that installation was a snap, so they’re not normally ready to hear or want to understand all that goes into proper calculations regarding gas line sizing requirements. That’s our job — having the skills and resources available to make intelligent decisions based upon factual information garnered by a jobsite visit.

For starters, how did the store’s personnel arrive at the sizing for this log set and how much usable heat is given up to the living space? More often than not, the sizing was based upon the dimensions of the fireplace combustion chamber with little, if any, consideration given to Btuh output.

But you didn’t make the sale. You’ve simply been asked to figure out the installation price.

Aside from the normal installation issues regarding the chimney (if it’s a vented appliance) and routing of the gas line itself, you need to discover who is responsible for assembly of the log set and the accessories.

If it’s a “vent-free” appliance, safety considerations must be discussed regarding fresh air, chimney cleaning and CO detectors. CYA (cover your assets)!

Now the interesting and more technical challenge begins. This is where you separate yourself from the untrained who have thus far been involved in this transaction!

Take a look at the drawing detailing the gas appliance loads and gas line sizes that already exist (in black) and where Harry the Homeowner wants you to connect because, after all, there’s a plugged fitting already in the line from a previous gas dryer that’s no longer being used (he bought an electric dryer because it was cheaper).

Maximum capacity shown in the drawing is for black iron piping for gas pressures of 0.5 psig or less and a pressure drop of 0.3-in. water column. This chart is based upon a specific gravity of 0.60 and 1,000 Btu per cubic foot for natural gas.

My old gas manuals call for sizing to begin at the end, so let’s back our way out of the home’s lines. The Range line can easily accommodate its load of 45,000 Btu as can the Oven line. Old Branch #2 needed to carry 95,000 Btu for 45 ft. of 34-in. pipe, which it could, but what about adding that new 35,000-Btu load from the gas log set?

In order to calculate this, we need to divide up the branches and start over.

Thirty-five feet of 34-in. pipe can carry in excess of 130,000 Btu, so we are home free, right? We’ll see. At 35,000 Btu and 35-ft. line length, the gas log set needs what size?

Moving on to Branch #1, we can determine both lines are adequately sized. Bringing all this together, we’ve got a pre-existing load of 283,000 Btu on a 30-ft. long, 1-in. gas line. We’re being asked to add another 35,000 Btu for a new total of 318,000 Btu. The homeowner’s belief, instilled by that freckle-faced kid at the DIY center, that there’s nothing to this installation has got to be revised.

What to do and how you resolve Harry the Homeowner’s problem can be as creative as time and materials allow! Let’s look at a few possible resolutions:

l We can cut into the 1-in. line as it enters the building (up to a little more than 20-ft. developed length from the meter) and tap in for a 12-in.-by-70-ft. run (if we mirror the existing routes) and the 12 in. can carry a maximum of 46,000 Btu.

l Run out to the meter and add a new branch connection. This will require another wall sleeve and at 90-ft. total line length; a 12-in. line can carry 40,000 Btu.

l Once again starting at an outdoor tapping by the meter, you could run tubing around the perimeter of the building, but that will necessitate an increase in line size to 34 in. for at least a portion of the run.

l Or you can offer something new and different! Corrugated stainless steel tubing run either from that indoor tapping within 20 ft. of the meter or, better yet, a CSST home-run system that offers Harry the peace of mind you can instill by demonstrating the ease with which any member of the family can isolate any single appliance for service.

Well, we kind of jumped ship by referencing the CSST tubing! That’s one of the cool things about the changes we’ve seen in the trades these past few years. It’s been challenging to keep up with the myriad of new products (a certification is required to install CSST tubing), but each one of these new products adds yet another weapon to your arsenal.

Dave Yates owns F.W. Behler, a contracting company in York, Pa. He can be reached by phone at 717/843-4920 or by e-mail at [email protected].

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