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Old 11-23-2012, 07:31 PM   #1
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Portable Natural Gas Generator - Gas Supply


I would like to connect a portable generator to the quick connect current used by a NG Grill. The generator a 6500 watt Honda unit:

http://www.generatorsales.com/order/...00iSA_Tri_Fuel

It consumes 95 cu. ft. / hr at full load.

The generator would be used to power critical circuits, including a gas furnace, cooktop and dryer.

The gas piping that is in place is shown in the attached diagram.

Would the 3/4 inch line currently servicing the gas grill suffice?
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Portable Natural Gas Generator - Gas Supply-gaspiping.jpg  

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Old 11-23-2012, 08:15 PM   #2
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Portable Natural Gas Generator - Gas Supply


Provided that your measurements are correct and none are missing, and your pressure is 7-14" wc, you would be sizing from the 70' code zone: the max capacity for 3/4 NPS is 166 mbtuh, so you're good there. Depending on the load of your furnace, dryer, water heater and cooktop, plus the generator, your 1" may not be large enough (312 mbtuh@ 70' code zone).

And one final thing: a dryer is a critical appliance?

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Old 11-24-2012, 09:44 AM   #3
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Portable Natural Gas Generator - Gas Supply


hvac_benny thanks for the reply it was very helpful. Some additional information:

Total Gas Appliance load: 198,000 BTU
cooktop 38,000
Hotwater 40,000
Dryer 20,000
Furnace 100,000
The Dryer is a nice to have if I can swing it.

My measurements are pretty accurate, the 90 in the 1 inch line is actually comprised of two 90s allowing a drop of a few inches to clear the floor joists.

I am not sure how to determine the supply pressure, here is a picture of the regulator(?) and the meter. There are no markings on the regulator that I can see. There is a second gas meter connected to the regulator that supplies a 355,000 BTU pool heater (not critical). I assume that can be ignored.


If I understand your comments correctly then the 1 inch pipe can supply 312 mbtuh over a distance of 70 ft and the 3/4 line can supply 166 mbtuh, how long can the 3/4 inch line be an maintain that volume?

If all the calculations are correct then I have about 114 mbtuh to run a generator.
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Portable Natural Gas Generator - Gas Supply-supplyreg.jpg   Portable Natural Gas Generator - Gas Supply-supplymeter.jpg  
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Old 11-24-2012, 12:02 PM   #4
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Portable Natural Gas Generator - Gas Supply


Quote:
Originally Posted by joabraun
hvac_benny thanks for the reply it was very helpful. Some additional information:

Total Gas Appliance load: 198,000 BTU
cooktop 38,000
Hotwater 40,000
Dryer 20,000
Furnace 100,000


The Dryer is a nice to have if I can swing it.

My measurements are pretty accurate, the 90 in the 1 inch line is actually comprised of two 90s allowing a drop of a few inches to clear the floor joists.

I am not sure how to determine the supply pressure, here is a picture of the regulator(?) and the meter. There are no markings on the regulator that I can see. There is a second gas meter connected to the regulator that supplies a 355,000 BTU pool heater (not critical). I assume that can be ignored.

If I understand your comments correctly then the 1 inch pipe can supply 312 mbtuh over a distance of 70 ft and the 3/4 line can supply 166 mbtuh, how long can the 3/4 inch line be an maintain that volume?

If all the calculations are correct then I have about 114 mbtuh to run a generator.
To determine supply pressure you could just ask your gas supplier. I'd assume it's 7-14" wc (low pressure) because if the size of your pipe. If there are no regulators after the meter, you have low pressure. The regulator you have is a Fisher S402, which can be used for low or high pressure, and the meter itself simply measures the gas and has nothing to do with regulating pressure.

Your second gas meter will not come into play as far as sizing your gas lines, but you do want to ensure that the utility's reg and meters are able to meet your load demand. That would be a question to ask your particular gas utility. Here, you'd be ok provided that the regulator you have has a 3/16th orifice(should be stamped around the outside of the reg where the screws are, i can see where it says orifice, but not the size), but you would be close to maxing out. Again, ask your utility.

Gas pipe is sized according to the longest measured run, in your case that is 67'. This determines the code zone (70' in your case) and is what all pipe in that system will be sized by. If you lengthen any runs to beyond 70', you are now in a new code zone, and will have to assess and possibly resize accordingly. Each code zone will tell you the maximum capacity that each size pipe can carry.

Each pipe is sized by the total load it supplies. Your 1" pipe supplies all appliances, so it must carry the max btu load. As you branch off, you can drop any loads not being served by that branch. For example, the 3/4 to the bbq connection only has to supply the generator's load, whereas the branch to the furnace, hwt and cooktop only has to supply the combined load of those three appliances.

Last edited by hvac benny; 11-24-2012 at 12:14 PM.
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Old 11-25-2012, 09:04 AM   #5
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Portable Natural Gas Generator - Gas Supply


I put on my glasses and took another look at the regulator. I rubbed the area with a wet glove and found:
SPG: 7.5 - 9.5 IN. WC.
ORF: 1/8 inch

Thanks again, I think I have enough info to talk to the gas company...
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