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Installation Talk Questions/Concerns and help involving the installation of a Guardian Automatic Generator

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Old April 16th, 2009   #1
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Join Date: Apr 2009
Location: Houston, Tx.
Posts: 24
Default Will I need to upgrade my gas meter?

I am looking at installing a Guardian 20kW standby generator (Model 5744).

The distance (linear ft. of pipe) is approx 25' between my American Meter Model AC-250 MAOP 5 PSI.

Is this meter capable of supplying enough natural gas to run this generator and also supply the following appliances:

Gas Range with
(6) 15,000 BTU Burners
(1) 18,000 BTU Grill

40 Gal. Gas Water Heater
(1) 32,000 BTU

Gas Furnace
(2) 75,000 BTU

Obviously, everything doesn't run simultaniously.

Thanks for your help.

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Old April 16th, 2009   #2
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Join Date: May 2008
Location: Southeastern Wisconsin
Posts: 2,925

The specs for the generator say that it will consume 294 standard cubic feet per hour (SCFH) at full load. You must specify your gas supply by adding that to the total possible load in the house which is, according to your numbers, another 140 SCFH (approximately 1000 BTU per standard cubic foot).

The meter is specified to handle 250 SCFH (see the sales brochure for the meter). It isn't big enough to handle the generator alone much less the whole house. You'll definitely want to bump up to the 425 size meter.

Make sure you get a proper (to code) calculation of the correct pipe size for delivery to the generator. You need to deliver the gas (under full flow) to the generator at about 7" water column pressure.
Skip Douglas

Last edited by SkipD; April 16th, 2009 at 08:34 PM..
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Old April 17th, 2009   #3
Join Date: Aug 2007
Posts: 36

After I installed our 5243, the gas company calculated and sized my meter based on everything running at the same time, which I understand is the way they are supposed to size the meter.

The only problem I encountered with this was that the pipe supplying fuel to my meter from the main in the street was undersized.

It was only 3/4 inch and should have been 1.25 inch size for the volume required.
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Old April 17th, 2009   #4
Join Date: Mar 2009
Posts: 30

Does your street connection sizing take into account that the street line is running at much hogher pressure that the lines going to the generator?

I can see that the generator line for my anticipated 20 kW should be 1-1/4, but that is only running at 7-11" of W.C

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Old April 17th, 2009   #5
Join Date: Aug 2007
Posts: 36

My issue wasn't so much with pressure (5" - 7" WC) as it was with volume. When my home was built it only contained an 82,000 BTU furnace and a 40,000 BTU water heater. Hence the gas company only ran a 3/4 inch line from the road main to the meter. This had a maximum supply of somewhere around 415,000 BTU's?

Over the years I added a gas range, gas clothes dryer, gas fireplace, gas bbq, and then I threw my 15/16 Kw generator into the mix. My gen set alone under full load needs 245,000 BTU's. When the gas company figured it all out, they deemed we needed to upgrade the underground pipe to 1.25 inches from the road main to the meter for volume. Oh and a bigger meter of course.

Last edited by Gentleman; April 17th, 2009 at 02:27 PM..
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