Gas pipe size

Empire_2

I see you thoughts and I think you meant 14"W.C. not ounces pressure gauge....:-) This set up sounds like an Octopus. 1 Cu..ft" = 1000 BTU/HR @ Specific gravity of 0.06. Altitude can change this factor. but in general if you are firing 270M, you need "X" factor coming in to satisfy your load. Length is critical in that where is everything taken off from?. 3/4" line for 270M NO WAY......

Mike T.

Paul Fredricks_5

I'm trying to figure out if a customer's gas line is big enough to add a water heater with a great BTU input. All the connected appliances, including the dryer and cook top, add up to 270,000 btu's. They have 3/4" black pipe from the meter, which then branches off to the various appliances. From the meter to the furnace room is about 25'.

I'm trying to use the charts in the National Fuel Gas Code book. If I figured it correctly the max demand is 265 cubic feet of gas. What I don't know is the pressure of the line. Is there standard psi between the meter and the units pressure regulator?

Please let me know if I'm doing this right.

jackchips_2

Hi Paul,

This reply is only in regards to natural gas and I'm in Massachusetts.

The maximum pressure for a low pressure system is 14 ounces and most systems run between 5 and 14.

A residence 3/4" line with a total equivalent length of 25 feet (from the meter to the farthest appliance) will supply 166 CFH of gas at approximately .3 pressure drop. Boston prefers .2 which would change the size a little.

You would have to add all BTU's required from the meter to the farthest fixture to determine the "load" on the line and size the main accordingly.

Therefore if your load is 270,000 and you add a 50,000 btu heater with the equivalent length staying the same you would require a main from the meter to furnish 320,000 btu of 11/4" although 1" would supply 313 btu and the diversity factor would probably allow the entire system to work.

Most of my engineering data is at work and I'm working off some old information here at home so hopefully someone else will double check.

Good luck,

Jack

Steve_35

If there are no external regulators

other than at the meter, natural gas usually runs about 7"WC. You need to find what's the maximum allowable pressure drop in your area. Here it's 0.5"WC.

Make sure you count the fittings and use their EL when figuring the TEL of the runs.

We were called in to quote a furnace replacement last week. The existing equipment is:
120,000 furnace
117,000 tankless WH
35,000 Tank WH
20,000 dryer
65,000 stove And da da da
250,000 pool heater

607,000 total input on a 1" black main with a 275 CFH meter. The really scary thing was I was the only one to quote them new gas piping along with coordinating with the gas company for a new meter. We got the job. There is justice sometimes after all.

Paul Fredricks_5

Thanks everyone. I'm going to have to run back out there and double check the pipe size. And I didn't think about TEL, so I'll have to try and figure that out too. Most of the piping is hidden in walls so I'll have to do some guessing.

FYI, it is natural gas. My 270,000 is as follows: 75K water heater, 125k furnace, gas dryer 35K (per fuel gas code), 40k cook top (per fuel gas code).

Steve_35

FWIW, the dryer is most likely high.

We find most residential dryers are 20k input, but I'd guess the range is probably low. We generally use 65k input if the data isn't available.

You may want to check the size of the meter as well although you're probably okay there. 275cfh is what we find on most older installs around here.

Paul Fredricks_5

I'm an oil guy. The meter size is on the name plate, correct?

Steve_35

On a plate or cast in the body front. nm

jackchips_2

Hi Paul,

As Mike T. suggested, let's change ounces to inches water column.

Here in the office my trusty wheel tells me that you can run 350,000 BTU's through a 1" pipe at a .3 pressure drop and 25 equivalent feet of pipe (pipe and fittings).

3/4" pipe can handle 170,000 BTU's at the same parameters.

11/4" pipe can handle 600,000 BTU's.

The meter should be fine. When doing large commercial projects we always check with the gas supplier to be sure their service and meter can handle the new load.

Hope this helps,

Jack

Al Corelli_2

Wheel?

Where did you get this wheel?

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