Tankless water heater Rinnai R98LSi QUESTION

Mimibuick · 03-13-2012, 03:09 PM

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?

Plumber101 · 03-13-2012, 07:24 PM

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.

Mimibuick · 03-13-2012, 07:36 PM

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.

Plumber101 · 03-13-2012, 08:07 PM

So post me your calculations using a 100K BTU furnace.

Mimibuick · 03-13-2012, 08:58 PM

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.

Plumber101 · 03-13-2012, 09:15 PM

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.

Mimibuick · 03-13-2012, 09:54 PM

^

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.

Plumber101 · 03-13-2012, 10:08 PM

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.