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Posted: 1/17/2006 11:28:44 AM EDT
[Last Edit: 1/18/2006 5:53:49 AM EDT by Andrewh]
When someone says you need a 3/4 inch gas pipe, what are they measuring? Is that ID or OD, and if it is ID, what would the OD be on average?

I know it is a 1/2 inch pipe now. measured .89 inch OD.
I think the max flow is 170k BTU, and they say the new tankless needs near 190k-200k. Anyone know the max for sure?
Link Posted: 1/17/2006 11:34:14 AM EDT
Eyeball it.
Link Posted: 1/17/2006 11:36:04 AM EDT
If I remeber correctly Gas Pipe is OD. It is usualy printed all over it. I don't know about the ID measurement of gas pipe. I know that the ID and OD of copper varies by and 1/8. If all else fails, get a fitting and put it on the end and you will know what you have.
Link Posted: 1/17/2006 11:36:08 AM EDT

Originally Posted By SubnetMask:
Eyeball it.



+ JB weld
Link Posted: 1/17/2006 11:36:30 AM EDT
[Last Edit: 1/17/2006 11:37:42 AM EDT by FITTER]
I'm assuming that you are talking about schedule 40 pipe or "black pipe."
Inside diameter generally determines pipe size, while OD determines tubing size. 3/4" pipe should be about 3/4" ID. According to the book, it specs out at .824" ID and 1.050" OD.
Link Posted: 1/17/2006 11:37:36 AM EDT

use one of them tape-like measuring devices that I'm sure your wife has to get the circumference, then google for the formula that changes circum to diameter. Atleast, that's what I had to do last time
Link Posted: 1/17/2006 11:37:46 AM EDT
See I was wrong.
Link Posted: 1/17/2006 11:45:17 AM EDT

Originally Posted By Scagnettie:
If I remeber correctly Gas Pipe is OD. It is usualy printed all over it. I don't know about the ID measurement of gas pipe. I know that the ID and OD of copper varies by and 1/8.



You're probably thinking of refrigeration line. Although the specs are the same, the terminology is different. 3/4" copper pipe is, indeed, 1/8" larger OD, measuring 7/8".
7/8" refrigeration tubing would technically be the same thing, except it comes plugged and purged with nitrogen. They are both the same size (we're talking copper here), although one is considered pipe while the other is considered tubing.
Link Posted: 1/17/2006 11:45:27 AM EDT
You can't eyeball it without looking past the Sphincter.
Link Posted: 1/17/2006 11:51:08 AM EDT
Beat me to it.

My gas pipe is OEM diameter thank God. ;)
Link Posted: 1/17/2006 11:51:30 AM EDT

Originally Posted By blackbag223:

Originally Posted By SubnetMask:
Eyeball it.



+ JB weld



+ an O ring for the extractor!
Link Posted: 1/17/2006 11:52:43 AM EDT
Link Posted: 1/17/2006 12:39:36 PM EDT
Let me try again, but I think I got the answer.
I am still looking at hot water heaters, and one company said I could not go tankless without a gas pipe change.
Another I went through to get a standard tank one started pushing the tankless one again. Since I never had the first company come out,(they wanted 40 bucks to look around,) I wanted to make sure the second one doesn't try to sell me something that won't work. Both agreed that a 3/4 gas line would be necessary. I have a set of dial calipers so I can check the OD, but didn't know what I was checking for. It is the standard black steel pipe coming out of the wall to the hot water heater.
So if it is 3/4 pipe, I should see a little over an inch, if it is less than that, it is 1/2 pipe?
Link Posted: 1/17/2006 12:52:17 PM EDT
[Last Edit: 1/17/2006 12:53:11 PM EDT by JB69]

Originally Posted By Andrewh:
Let me try again, but I think I got the answer.
I am still looking at hot water heaters, and one company said I could not go tankless without a gas pipe change.
Another I went through to get a standard tank one started pushing the tankless one again. Since I never had the first company come out,(they wanted 40 bucks to look around,) I wanted to make sure the second one doesn't try to sell me something that won't work. Both agreed that a 3/4 gas line would be necessary. I have a set of dial calipers so I can check the OD, but didn't know what I was checking for. It is the standard black steel pipe coming out of the wall to the hot water heater.
So if it is 3/4 pipe, I should see a little over an inch, if it is less than that, it is 1/2 pipe?





Yes...... 3/4" pipe will be approximately 1" external diameter, probably a little bit over.

1/2" pipe will be approximately 3/4" external diameter, again, prob. a little bit over.


This is for black iron pipe only, but you wont SEE copper gas line often, unless you're in the building trades. It's actually used for underground utility co. feeders to your house, and some 'flexible' connector pipe is made out of copper. (looks like bendy straws)


I'm no plumber, (just a dumb wire puller) but we had an on-demand gas water heater in our house when I was younger. I'm pretty sure we had 3/4" black iron. They DO work nicely tho, that much I CAN say for sure
Link Posted: 1/17/2006 12:58:33 PM EDT
Thanks.
Link Posted: 1/17/2006 1:04:48 PM EDT
Pre-Brokeback Mountain gas pipe, or Post-Brokeback Mountain?
Link Posted: 1/17/2006 7:07:52 PM EDT
Most of the gas lines I run into are 3/8 or 1/2 inch!!! Some may be 3/4 or one inch! They will be black pipe!

You can couple up or down with a bushing!!

Bob
Link Posted: 1/17/2006 7:21:15 PM EDT

Originally Posted By vito113:
Saw it in half and take it to the hardware store...



It's easier if you use a cutting torch.
Link Posted: 1/18/2006 5:52:20 AM EDT
I know you can up size and down size, but I understood it was a supply issue. It doesn't increase supply by installing a coupling to move it up from 1/2 inch to 3/4.
It has to go from supplying around 40k btu to as much as 190k btu. I think 1/2 inch (which I am pretty sure I have now, since it measured about .89 OD,) maxes out at like 170btu. Well, depending on how far it is tapped off from the one inch main.
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