Gas line for 400k btu Natural gas heter

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BigJD

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Jun 6, 2008
176
Folks,

Just looking to poll to experts and pool owners. What size natural gas line do you have hooked up to your 400k btu heater?

I ask because a good friend and neighbor of mine says the 1.25" is overkill for the volume required. He says a 1" line is more than sufficient. He is also a gas fitter for a local utility company so I trust his judgment.

Thoughts? :?

JD
 
This depends on many factors. Pressure, type of pipe, and length of pipe.
If you are less then 10' away from the meter then 1" is fine.
I personally always run 2" to heater location. This gives us some future size to use if needed.
 
The meter output is typically 7 lbs in-wc ... heater only expects 4-5 lbs in-wc at the reg and 2-3 after ... seems like it would be fine ... I already have a 1" main in from the meter and down the center of my basement ... this would minimize the pipe install.
 
See this table and this file. 400,000 BTU/hr is a little less than 400 cubic feet per hour. A 1" line should not be longer than about 25 feet for this capacity. And that doesn't include the total of all other gas devices used in your home, assuming the line size you are referring to is the pipe from the street to your meter. A 1.25" would let you get to around 100 feet of pipe. Note that the chart is for sizing that allows for a 0.5" water column drop which for typical 0.5 pound gas pressure delivered to the meter (equivalent to 13.8 inches of water column) is for a roughly 4% loss in pressure.
 
I know that I have around 60-70 feet of 1/2" gas line feeding my furnace (100k btu) in the attic with no issues ... which according to this chart would not work. Hard to argue with the math (I am a mech. eng.)
 
It just means that you are getting a larger drop in gas pressure, more like 16%, by the time it reaches your furnace. It doesn't mean that it won't work -- it depends on the actual pressure the device expects or needs in order to function properly. The tables are conservatively sized for a 4% pressure drop, but that's code which is fairly consistent across the nation in terms of these tables. This link contains Table A.3.4 and Figure A.6(a) that is more clear about the pressure drop per 100 feet at various flow rates and pipe sizes while this link has a useful calculator for calculating flow rates given pipe size and pressure drop.

In JD's case using 1" pipe, he will lose 2.7" water column per 100 feet of pipe which is 19% of total pressure (assuming starting pressure of 0.5 pound or 13.8" water column) per 100 feet of pipe. With 1.25" pipe, he will lose only 0.56" water column per 100 feet which is only 4% of total pressure per 100 feet of pipe.
 
BigJD said:
Folks,

Just looking to poll to experts and pool owners. What size natural gas line do you have hooked up to your 400k btu heater?

I ask because a good friend and neighbor of mine says the 1.25" is overkill for the volume required. He says a 1" line is more than sufficient. He is also a gas fitter for a local utility company so I trust his judgment.

Thoughts? :?

JD
Click to expand...

1" is too small. You need at least 1.25" at <50 feet to bring enough gas to that 400k heater. 1.5" is better. You need 2-3" WC at the heater. Be sure and have the gas company check the meter to see if its big enough. 1" wont give you enough gas unless you're right at the meter.
Personally, i dont like 7" service at the meter. I'd rather have 2 psi on the street, and go with a 2 stage system. That way you can use smaller pipe initially, have more gas at the 2nd regulator, and be assured to have adequate gas to the heater. Barring that, you should be fine with a single stage system under 100 feet. Again, have the gas company check and make sure you meter is big enough and doesnt have to be upsized.
 
bk - the meter definitely has to go up , right now i have a 325 ... my max load in the house is 360. Probably will need a light commercial meter. I have 7" after the meter ... I hear I have 50"+ at the street ... the difference is between extending my 1" trunk line 15' and running 50' of 1.25 ... it comes down to material cost (neighbor will pull permit etc) which is not really significant considering the cost of the pool. Better safe than sorry I guess.
 
Ok, you have 2 psi on the street. Talk to the gas company (Nstar?) and see what they want to do. A bigger meter for sure. See if they do a 2 stage, or go with a single stage and a bigger pipe. Some companies like the single stage, some will do a 2 stage. It all depends how they like to set everything up.
 

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We recently had to replace our 400K BTU natural gas heater line because the existing one was made of black steel and had rusted through. We have a 1 1/2 inch yellow polyethylene (PE) line that runs about 100 feet from the main regulator to the heater. It seems to work great.
 
They won't do poly pipe for residential installs here (although it is fine fir commercial). Most of my pipe will be in the house. The 10-15 feet that will be buried will be black iron with a poly wrap tape.
 
I have about a 120 ft run on mine, going to do a 2 stage, dropping to house pressure again right at the meter. Like you said its all about costs. MUCH cheaper this way, and assured good performance by dropping pressure right at the big consumer of gas.
 
BigJD said:
My pipe is in ... inspection tomorrow. 120' of 1 1/4, total out of pocket including permit is $400. Not bad :)
Click to expand...

I have the same question but am a little confused with the answers. We are going to be installing a 2PSI meter at the house. We will need a regulator on the house line to keep the pressure down. We will have a Pentair 400K BTU natural gas heater. The run is about 130ft. From an internet search, it looks like the proper gas line to run is MDPE. 1-1/2 MDPE seems to be sold in 500ft rolls. I saw 1-1/4 MDPE (1-1/4" IPS SDR11 PE2708 Yellow MDPE Gas Pipe 150' Coil - Hdpe Supply) for $180. Anyway, what size/type of pipe do I need for this run? What type of regulators will I need?
 
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