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# Is the gas pipe big enough

#1
03-26-11, 01:01 PM
Member
Join Date: Jun 2007
Location: NYC
Posts: 206
Is the gas pipe big enough

I have a 1 1/4 in natural gas pipe thats hard to get to reduced down to a 1 in natural gas pipe thats easy to get to.I would like to know if the supply would be large enough to run --Goodman furnace with a BTU of---115,000,Gas dryer---20,000 --plus Rinnai (tank less) -9,500 at 199,000 BTU/H.The 1 1/4 gas pipe is about 26 feet from the gas meter,with nothing coming off except the two appliances stated above that comes off the reduced 1 in.Would I be able to go into the 1 in or would I have to go into the 1 1/4 in.Thanks for any help.

PS:Yes might not be cost effective but my friend wants to go with tank less.

#2
03-26-11, 01:10 PM
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Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 18,159
Good you made a decision. Nothing wrong with it, we just wanted you to make a informative decision.

I can calculate for you but how far is the meter from where you want to put the tankless?

It probably will be easier to run flexible track pipe right from the meter. Most likely 3/4. The inlet to the tankless are 3/4 and this would be the minium size ran.

If you want to tie into the black pipe then I got :

26ft 1 1/4 correct?

How many ft of 1" And does 1" run all the way to the last appliance?

26 ft plus how many more ft of waterever pipe to the farthest appliance?

The appliances break down to 1/2 " or 3/4 off the 1" line correct? How many ft of pipe off the 1" for each appliance?

Mike NJ

Last edited by lawrosa; 03-26-11 at 04:04 PM.
#3
03-26-11, 04:27 PM
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 18,159
Its best if I had a drawing like this. You can put in pipe size and ft then we can figure if you can tap into the line.

The blue # are ft of pipe

The letters are just a reference. Ex : A - 1 1/4 B- 1" etc....

Mike NJ

#4
03-26-11, 04:59 PM
Member
Join Date: Feb 2011
Location: N. Calif.
Posts: 48
So all 334K btu are on the 1" ? How may feet?
1 1/4 will carry 334k up to 125'. So far so good.
1" will carry 334k up to 30'
Add up the TOTAL developed run starting at the 1". That is the length of the run and the branches..
Under 30' and you should be ok. It is imperative that you connect to the heater with 3/4. Dont shortcut this.
I troubleshoot tankless heater for one of the manufacturers. Most failures are directly or indirectly related to undersized gas. Dont use one of the yellow "3/4 rated" flexes either. There is high volume flex specifically for tankless heaters. It is a 1" i.d. hose with 3/4 fittings, if you dont hard pipe it.

#5
03-26-11, 06:22 PM
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 18,159
So all 334K btu are on the 1" ? How may feet? 1 1/4 will carry 334k up to 125'. So far so good. 1" will carry 334k up to 30'
You need to reverse engineer the gas calculation. It does not work that way. You need to take the farthest appliance and work off that column (ft wise) for all piping back to the main.

So your 1 1/4 above that you say will carry 334K at 125 ft is not true.

If your distance to the farthest appliance is 60ft then you need to work off that column for all piping. Work backwards to size your pipe to the BTU for the mains/branches etc.... But you are working off that footage column. If the BTU does not match then you need to go up a size pipe.

Lets take the gas grill in the diagram below. That is the farthest appilance @ 85 ft. So we will work off the 90 ft column in the gas code.

Example:

J,K,L in the 90 ft column @ 40,000 btu. Would be 1/2". JKL = 1/2@90 ft = 53,000 btu
I, in the 90 ft column @ 125,000 btu. Would be 1" I= 1"@90ft =205,000 btu. (ex:3/4 only supplys105K)
H in the 90 ft column @ 125K +40K = 165,000btu H= 1"@90ft =205,000 btu.

And you keep working back to the meter.

Then you take this same schematic and add your new appliance and do it all over again. If any of the exsisting pipe is not the correct size then you cant tap in.

This is gas piping 101 and thats how the charts work. Now if he came off the meter then you can just calculate ft and btu.

So if his tankless was 60 ft from the meter he would need to run a 1" line from the meter @ 285K btu. 3/4 at 60 ft is only 138K btu and his unit needs 199K btu.

Mike NJ