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Old 10-31-2011, 01:55 PM   #1
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Additional "T" in gas line for furnace?


I need to run a gas supply for the furnace. Is there any reason I can't add an additional "T" to the line that is supplying the hot water heater? Or do I have to run an additional 1/2" off the main line? (The 3/4" main is a long continuous piece and it would be significantly easier to just piece together off the hot water heater supply) Picture below should explain my question. This in a partial basement so the 3/4" Main is overhead and the 1/2" line is running down the side of the wall.
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Old 10-31-2011, 02:44 PM   #2
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Additional "T" in gas line for furnace?


Not a pro here but I have never seen a setup in our area in which each unit didn't have its own feed off the gas main line or manifold. I would bet that is code... or at least a sizing issue as the 1/2" line would probably be too small to supply both furnace and water heater simultaneously. My own house has separate 3/4" lines for furnace (80 kbtuh) and water heater (40k btuh). Just my observations and guess... the pros can answer for sure.


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Old 10-31-2011, 03:14 PM   #3
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Additional "T" in gas line for furnace?


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a sizing issue as the 1/2" line would probably be too small to supply both furnace and water heater simultaneously
That would be my guess too. A 3/4" line has 2.25x the volume of a 1/2" line. I believe it may also depend on the lengths of the runs and the gas requirements of the appliances.

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Old 10-31-2011, 05:21 PM   #4
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Additional "T" in gas line for furnace?


What else comes off that 3/4 " line? I would run 3/4 from the main 3/4 over to the heater then drop to 1/2 after the furnace to the water heater.
Wait to hear from some gas jockeys what they say. Don't take my word for it. Or you can calculate it by looking up the size of the pipe and the pressure how many BTU's it can handle then add up the BTU's of the water heater and the heater.
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Old 10-31-2011, 05:47 PM   #5
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Additional "T" in gas line for furnace?


It would be helpful if you state the size of the gas appliances you are piping, btu rating of both the furnace and the HW heater.

This way I am sure you will get far more qualified answers.

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Old 10-31-2011, 06:02 PM   #6
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Additional "T" in gas line for furnace?


furnace is a 50k BTU, the hotwater heater I'll have to look up when I get home.
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Old 10-31-2011, 06:48 PM   #7
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Additional "T" in gas line for furnace?


yes coldiron is right....I would run 3/4 off main to furnace use 3/4 x3/4 x1/2 tee with 1/2 inch droping to furnace then i would run alittle more 3/4" pipe for volume then reduce to 1/2" for water heater......1/2"to supply 50,000 btu furnace and 30-40,000 btu heater is to small... what is the total length from main to water heater

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Old 10-31-2011, 06:57 PM   #8
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Additional "T" in gas line for furnace?


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what is the total length from main to water heater
little more than 5ft
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Old 10-31-2011, 07:42 PM   #9
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Additional "T" in gas line for furnace?


I just looked up maximum capacity of pipe in cubic feet of gas per hour based on pressure drop of 0.3 inch water column..it says 10 foot length of 1/2 pipe can handle 132 cubic feet of gas per hour..sooooososoo I guess that would mean your five foot length of pipe should handle this load.....however I still like my idea and coldiron suggestions....ben...... this chart is from gas pipe sizing from burnham heating helper.....hope this helps
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Old 10-31-2011, 08:34 PM   #10
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Additional "T" in gas line for furnace?


You need to measure from the meter, or last regulator, to your farthest appliance to determine the total volume that the pipe can supply. From your original sketch, it would appear to me that there may be another appliance being fed by the gas line? Is there perhaps a range or fireplace farther down the line?
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Old 10-31-2011, 11:32 PM   #11
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Additional "T" in gas line for furnace?


Scratch,

The proper way to size piping for gas appliances is to know the piping loads, longest measured run and the code zone.

Piping loads means the volume of fuel that must pass through the pipe each hour. This volume is determined by the appliance load connected to that pipe.

Longest measured run is the distance from the point of gas supply (gas meter) to the manifold of the furthest appliance. This measurement must be the actual length of pipe as it is installed. Elbows, Tees, etc... lengthen the system measurements.

Code Zone is a series of tables (based on certain info including pipe wall thickness, system pressure, & pressure drop) that gas fitters have which help us determine the proper pipe sizes to use when installing & refitting gas systems.

Looks like you're pretty handy at sketching, so if you're willing to provide the piping loads & longest measured run, I'd be willing to look up the code zones and offer advice.

Gas is something that I wouldn't recommend half assing. It's either done properly or not at all.

You game?

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