Gas company says I don't need to upsize my meter

mmoore305

I have recently upgrade my hydronic heating and domestic hot water to both use tankless navien units. With these upgrades, the full max load calculates to 450k btu ~ 450 cfh.

I just had a Southwest Gas tech tell me that my 250cfh rated meter can handle that load because downstream of the meter (just before entering the house) it’s split into 3 pipes (through a series of T fittings) so I have to divide the load by 3.

Has anyone ever heard of this? Seems very dubious to me – if the diaphram is the limiting factor for flow, what does the splitting of the pipes downstream of the meter have to do with it?

The tech did say that when I add my generator, (+300 cfh) I’ll need to upgrade the meter (which doesn’t follow from his logic because if splitting it 3 ways gives me 3x, then I’d be able to support 750cfh which will be my new max with the generator…)

I dont want to damage my all of our new appliances by starving them for gas…. Do I need to push Southwest Gas on this?

ChrisJ

mmoore305 said:

I have recently upgrade my hydronic heating and domestic hot water to both use tankless navien units. With these upgrades, the full max load calculates to 450k btu ~ 450 cfh.

I just had a Southwest Gas tech tell me that my 250cfh rated meter can handle that load because downstream of the meter (just before entering the house) it’s split into 3 pipes (through a series of T fittings) so I have to divide the load by 3.

Has anyone ever heard of this? Seems very dubious to me – if the diaphram is the limiting factor for flow, what does the splitting of the pipes downstream of the meter have to do with it?

The tech did say that when I add my generator, (+300 cfh) I’ll need to upgrade the meter (which doesn’t follow from his logic because if splitting it 3 ways gives me 3x, then I’d be able to support 750cfh which will be my new max with the generator…)

I dont want to damage my all of our new appliances by starving them for gas…. Do I need to push Southwest Gas on this?

I'm hoping there was more that was said that maybe you missed.

What pressure is your system running at? Without knowing that, we can't really give an answer regardless of how everything is piped. A 250 meter will handle a whole lot of gas at 2 PSIG for example.

Rich_49

It is easy enough to look up how your meter performs at various pressures on the manufacturers site . At least it used to be . For instance , a friend of ours installed a Rinnai Tankless in the beginning of their existence in a large home with a 415k meter , the heater would not light when winter began and not always , it would light sometimes . Turns out that the 415 meter delivers 415 great with the installed 8" w.c regulator NJNG uses prior to the meter , at that condition the meter has a .5" wcpd through the meter but once you get above 415 that pressure drop becomes 2" wcpd , oops , now we have a problem because we replaced a 40K appliance with a 200K appliance on an almost maxed out meter . A Rockwell 750 meter solved the problem that the Schlumberger 415 developed . Mystery solved .

Tim McElwain

The meter needs to be sized to handle the full load at around 6" W.C. gas pressure. If the pressure being supplied is greater then you have to look at the capacity of the meter at the higher pressure.

EBEBRATT-Ed

@mmoore305

Unless you have a 2psi system the technician is clueless. The # of pipes after the meter means nothing

Tim McElwain

Size and length of run of the pipes has to be factored in at full load (everything running at the same time).