Questions about gas piping for tankless water heater

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Old 11-27-13, 09:24 AM
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Questions about gas piping for tankless water heater

Hi,
I am going to add a new tankless ng hot water heater (Takagi TH3DV) to my home. I currently have an electric 40gl tank which I will be removing. I do already have ng gas in the home but the supply is only rated at 175btu so that will need to be upgraded by the gas company. I have already arranged for this and it should be a non-issue according to them. Their only stipulation is that the work inside the home has to be completed before they will upgrade the meter.

I plan on hiring out the work for the gas line extension for the new tankless but I like to be educated on what goes on in my home by contractors especially if they start suggesting this or that before work. It also gives me a leg up when choosing a contractor that I can validate their suggestions as to what needs to be done.

I have included a drawing of the piping currently used, the length of the runs, and how everything is connected. It also shows where I want to place the tankless unit. I did not include the actual number of elbows as I read that this does not matter.

My questions are:
1. Does having a hot water heater off of the initial portion of the incoming line that continues feeding other appliances meet code or do I have to get a dedicated pipe from the meter?

2. Given that the system is low pressure (7" water column) will I encounter any problems given the length of runs and size pipe used? I did not show feet from the meter to wall but this is probably less than 1'. Maybe someone can point me to a resource I can use to figure out the calculations (if there are any to be done, this is a vague area for me).

3. My gas company also has the option to upgrade me to 'high pressure' which is 2.lbs. I understand that I would have to place regulators before each appliance or in the line at certain points so the appliances still get low pressure gas. Is this necessary given my current setup and what I want to do?

The only other spec I saw that might be of interest on the water heater is about the inlet gas pressure:
Min. 5.0 W.C. (1.24 kPa)
Max. 10.5 W.C. (2.61 kPa)


Thank you very much in advance for any insight you can give me.
-Igor

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Old 11-27-13, 03:23 PM
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Just run a dedicated line from the meter to the heater...

Easiest to do.. use trac pipe corrugated SS...

You will need to run 3/4 pipe to the 199 btu heater...Thats up to 30 ft... ( 1/2" is to small and will not support that heater)

If you do not run a dedicated line then you need to repipe most of the piping...

.Increasing the pressure then you may have to worry about joints leaking...
 

Last edited by lawrosa; 02-27-14 at 02:17 PM.
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Old 11-28-13, 08:50 AM
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Thanks for your reply Lawrosa.
I was thinking they could cut into the existing pipe and use a union to re-connect the original run and also a T join to split the run to the water heater. Maybe this is not possible or are you saying that doing that would not meet code because it requires a dedicated run?
 
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Old 02-27-14, 12:21 PM
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Thanks again lawrosa, what you suggested is what I ended up going with. 1" dedicated trac pipe to the heater and then convert down to 3/4. I should be set if I ever want to add an additional appliance.
-Igor
 
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