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Old 03-13-2012, 02:09 PM   #1
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Tankless water heater Rinnai R98LSi QUESTION


I have a customer that wants me to install a Rinnai R98LSi tankless water heater.
http://www.rinnai.us/tankless-water-heater/r98lsi/

The water pipes are not a problem and its only 5-6feet from an exterior wall for the intake and exhaust. Also easy to install anew outlet as well.

My concern is the gas pipe/supply. The tankless needs 237,000btu and his furnace doe not have a listing of its BTU so I have been running my numbers based on 80, 100, or 125k btu. The gas company says the meter will supply up to 325,000Btu but with a junction will supply 360,000Btu. I guess they mean putting a junction at the meter and then feeding 2 separate lines?
The pipe from the meter to the furnace/water heater is about 25-30feet. My CFH calculations have it either barley making it or failing if both were running at the same time, see winter.

I think they still want me to install but I am pretty sure I am going to have to turn it down, I am very conservative when installing anything running off of gas.

Am I being over cautious or does it sound like its to much to install off that meter?

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Old 03-13-2012, 06:24 PM   #2
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Tankless water heater Rinnai R98LSi QUESTION


Are you running a 3/4" gas line to the tankless unit?

Instead of using a Rinnai have you looked into Rheem where you can use PVC as the flue pipe. Rinnai flue pipe is so freak'n expensive.

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Old 03-13-2012, 06:36 PM   #3
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Tankless water heater Rinnai R98LSi QUESTION


Customer already bought the Rinnai so he really wants it installed. Ive installed tankless before but not to where the furance and tankless would eat up all the BTU/CFH that it could be supplied with.


But yea 3/4" water and gas.
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Old 03-13-2012, 07:07 PM   #4
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Tankless water heater Rinnai R98LSi QUESTION


So post me your calculations using a 100K BTU furnace.
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Old 03-13-2012, 07:58 PM   #5
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Tankless water heater Rinnai R98LSi QUESTION


The furance and Tankless are 337,000btu but the Meter I was told is good for 325k btu; but 360 with a "split".


I was using 1030 for the CFH to BTU conversion so I came up with 327CFH requirment. The meter information was given to me in BTU so I am thinking its rated at roughly 325CFH? Then subtract 10% for the pipe length (20-30feet) and I get the line can supply 292CFH at the end run. Even the 360 "split" number they gave would be right at the limit.

I just wrote him to tell him I will not install it. I lean toward it being safe as I am very conserative with my numbers as you can see. But safety comes first for me and if I would not do it in my own home I will not do it in someone elses.
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Old 03-13-2012, 08:15 PM   #6
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Tankless water heater Rinnai R98LSi QUESTION


If you are using the meter in the sizing of gas pipe and then subtracting a percentage for pipe length then I will say you need to learn how to size gas pipe, because the way you are sizing pipe is all wrong.

A meter being under sized is no big deal once you properly size the pipe for the appliances served. Just a simple call to the utility company stating that the meter is to small and they will change it out.

I would also caution you that if you are not a licensed and qualified contractor installing water heaters some and most code jurisdictions frown on this. Plus I hope that you are carrying general liability insurance because when something goes wrong it's all about the attorney's and insurance.
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Old 03-13-2012, 08:54 PM   #7
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^

As I already said, more than once, I did talk with the gas company. The meter they have is the largest for the supply line that is run to the house.
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Old 03-13-2012, 09:08 PM   #8
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Tankless water heater Rinnai R98LSi QUESTION


I haven't worked with an utility company yet that once it is explained to them that the total BUT's of a home is increased that they wouldn't figure a way to increase the gas supply to the house. And that is for both Gas and Electric.

Numerous times I have had to repipe a home to satisify the the required gas pipe size to service an appliance.

We just did a home that required 1 million BTU. 2" service in the house and 1" to the supply to the meter.

What I am saying is that a utility company isn't going to tell a customer that they can't have a tankless water heater because the meter is too small and they aren't going to help.

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