Gas line to new Rinnai R94Lsi


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Old 04-10-10, 09:46 AM
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Gas line to new Rinnai R94Lsi

I will be installing a Rinnai R94Lsi to suppy hot water to my two bathrooms upstairs. I am remodeling my master bath and the new multi-head shower will require more than my existing gas water heater can handle.

My question is regarding proper sizing of the gas line. The Rinnai requires a 3/4" line. The unit will be installed in my attic, approx. 55 feet from my gas meter. I have an existing 3/4" gas line that supplies my gas furnace, which is also in my attic. There is a union in this line, about 30' feet from the gas meter where I can easily install a t-fitting. I would then have a 25' run to my new tankless water heater and a 10' run to my gas furnace from the t-fitting.

Will this work? How do I determine if it will supply enough gas? I could run a new line all the way from the gas meter but would prefer not to if this will work.

I appreciate the help. BTW, I have a gas monometer, which I purchased when I installed my gas pool heater and have access to a gas pressure gauge as well.
 
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Old 04-10-10, 10:03 AM
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Anon, I've moved your post here to the 'water heater' forum, since the 'Home heating systems..." forum wasn't the right place.

There doesn't seem to be a place for your exact question regarding gas piping though, but hopefully someone here can advise.
 
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Old 04-10-10, 02:25 PM
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how many btu's is this water heater ?
 
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Old 04-10-10, 02:35 PM
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In order to figure if the line is large enough you have to know the btu rating of the water heater and the rating of the furnace. Also need to know if anthing else is connected to that line.
 
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Old 04-10-10, 07:27 PM
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The water heater is 199K BTUs and the furnance is 80K BTUs. Nothing else would be connected to that line.

Again, thanks for the help. Let me know if there is any other info you need.
 
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Old 04-11-10, 09:59 AM
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round it off to 60 feet at 300,00 btus

60 feet at 1 inch willonly give you 269 that is with no elbows count each elbow as 2 1/2 feet
60 feet with 1 1/4 will give you 532,000 what you can do is take the first 20 foot at 1 1/4 which will be plenty then 40 feet at 1 inch and that will be 322,000 btu's
 
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Old 04-11-10, 01:38 PM
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I decided to venture under the crawl space of my house to verify the gas line size and make sure nothing else is running off the line.

Well, I confirmed that nothing but the furnace is running off the line right now. However, the size of the piping for the first 26 feet is 1". Then it elbows up into the wall, still at 1". But, when it comes out of the wall into the attic, it's 3/4". Some place along the wall it is reduced from 1" to 3/4".

So if I read Wisehvac's post correctly, even with this new information, it sounds like I would not be able to run both appliances off the same line. So if I have to run a new line from the meter, am I correct in assume I need to run another 1" line since it will yield 269k BTU's @ 60'.

Is this correct?

Originally Posted by wisehvac
round it off to 60 feet at 300,00 btus

60 feet at 1 inch willonly give you 269 that is with no elbows count each elbow as 2 1/2 feet
60 feet with 1 1/4 will give you 532,000 what you can do is take the first 20 foot at 1 1/4 which will be plenty then 40 feet at 1 inch and that will be 322,000 btu's
 

Last edited by anonymouscuban; 04-11-10 at 02:03 PM.
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Old 04-11-10, 10:56 PM
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your correct but where you tie them two together you better use 1 1/4 if you go on a takagi websight and look at manual they will show you how to measure btu's.
one more thing what do you use for cooking and your dryer. before you go ad just add one line why don't you size the whole job out and do it all in one shot.
 
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Old 04-14-10, 04:53 PM
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OK...

I went under the house again to explore. Coming out of my meter I have a 1.5" line that supplies my home. This 1.5" line then branches off into a few lines a few feet from the meter, one being a 1" line that travels about 25', at which point is reduced to 3/4" and continues for another 20' terminating at my furnance. There are two elbows in that line... one 1" 90 degree just be it get's reduced to 3/4" and then another 3/4" 90 degree in the attic.

It is roughly 60' From the meter to where I want to place the tankless water heater. If my calculations are correct, a 1" line is required to supply the required gas volume for the tankless (190K BTU) at 60'.

My question is, can I tee-off the section of 1" pipe that is supplying my furnance and continue the run to the tankless in 1" and supply enough volume to both my furnance (80k BTU) and the tankless.
 
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Old 04-14-10, 08:51 PM
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I've posted this link several times. It is specifically for installing a generator but the principles are the same for all gas consuming appliances. It shouldn't take more than about ten minutes to do the arithmetic.

Natural gas piping

REMEMBER, gas piping is NOT the place to learn about fitting threaded steel piping systems. Unless you have experience with cutting, threading and hanging steel pipe I strongly urge you to have a licensed gas fitter do this work.
 
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Old 04-14-10, 11:47 PM
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why don't you fraw a diagrahm of what you want to do and I will tell you if its carrying enough gas now you have 280,000 btu's is that at the end of the run?

if not you have to add everything in that run up rigt to the first existing tee.
 
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Old 04-15-10, 09:24 AM
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Wise...

Thanks for all your help thus far. I think your suggestion of drawing it out will be my best bet. I'm taking tomorrow off so I plan on crawling under the house and outlining everything coming from the meter. No matter what, I think that will be a useful exercise.

Furd...

Your link was very helpful. Now I think I have a good understanding of how to size this thing properly. Judging by what I know to have on the line, I need to run 1'1/4" line to where it would branch off to the furnance and the tankless. From there, I can run 3/4" to the furnance and 1" to the tankless.

Again, I think I need to really outlined everything and post it so you guys can confirm what I am saying.
 
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Old 04-15-10, 09:16 PM
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OK.. here is the drawing of all the gas lines coming from the meter.



The total BTU consumption is 456K BTU including the new Tankless which is 199K BTUs.

The longest run to any appliance would be that to the new Tankless which is 70 feet from the meter. So looking at the pipe sizing charts on the net, I need a 1 1/4" line from the meter. As you can see, my trunk line is 1 1/4" so I think that is good so far.

The new tankless water heater location is 30' from the end of the 1" line marked G. My original idea was to replace line G with a 1 1/4" line and then run a 30' 1" line from there to the tankless.

But after looking at this, I think I have another option. I could replace the first 14' of line E with 1" and then tee off it with another 1" to line H and connect the furnance to this branch. Then I could leave line G as 1" and simply continue the 1" line another 30' to my tankless.

Am I making any sense with either of these options? If so, which makes the most sense?
 
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Old 04-16-10, 08:59 PM
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That came real close I don't think you added 2 1/2 feet per elbow and 5 feet per tee. You just came a little short on the left of the diagram I would you a 10 and a 5 foot bice of 1 1/2 just to be on the safe side.

on the 2nd half of your state ment you wanted to run 1 inch on left of diagram. You have to calculate how many fet of total you will lose dont forget atthe first tee you have 140 ptus on the right then going down and back oveer to left. the right side had less btu's then left side....... becareful nd measure again and use a chart. but your on the right trck
 
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Old 11-09-10, 10:49 AM
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Originally Posted by Furd
I've posted this link several times. It is specifically for installing a generator but the principles are the same for all gas consuming appliances. It shouldn't take more than about ten minutes to do the arithmetic.

Natural gas piping
Very useful link. What is the service pressure in the link. Based on the pipe sizing it looks like low pressure, just curious if it's 5/6/7" WC? I see that the pressure drop is 0.5 WC, but not sure on the service pressure, at the meter.
 
 

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