# Need to tap into gas line

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#### logwolf

##### New Member
Hello everyone
I'm installing a new gas water heater . I'm replacing the current electric water heater.
The location of the new heater will be a new location, more equidistant between the two bathrooms in the house. It will be located in a full basement, 50 x 27 feet(1350 SF).
There is a 3/4" gas line coming in from the meter. That line runs apprc 10 feet into the basement behind the gas furnace. The 3/4" line stops at a 3/4" T. This T is capped on one outlet of it. The tail section of the T has another 3/4" pipe running approx. 3-4 feet toward furnace where a 1/2" to 3/4" elbow is located. At the 1/2" end of this elbow, runs a pipe leading down to the furnace.
This is currently, the only gas appliance in the house.
The amount of black pipe I will need to run from the T to the new water heater , is approx. 40 linear feet.

My question is...Do I need to run 3/4" pipe to the area above the heater, then use 1/2" pipe for the vertical run down to heater area? OR Can I reduce the T connection down to 1/2" and run 1/2" all the way(40 ft), to new heater? Photo shows T fitting with plug.

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#### Stuff

##### Well-Known Member
How many BTUs is the new water heater? If standard tank most likely low enough that 1/2" is fine.

#### Phog

##### Active Member
You will need to start by looking up the btu/hr ratings of your two appliances.

Now measure the straight lengths of pipe that will be in each branch. Then, add in the equivalent length of each of the fittings, to calculate the total effective branch lengths. Finally, use a gas pipe capacity table to make sure your branches are sufficiently sized for the total btu/hr of BOTH your appliances. Based on what you describe it's unlikely you're going to be starving the existing furnace by adding in a water heater, but you should still check to make sure.

You can find tables with the fitting equivalent length & pipe btu/hr ratings easily with a Google search. Make sure you are finding the correct tables for your gas supply system pressure -- there are newer 2psi systems out there (mostly in newer construction) while older "traditional" gas pipes run at approximately 7" w.c. (1/4psi). You just want to make sure you're using the table that matches your supply pressure.

#### logwolf

##### New Member
Thank you for the replies. Forgot to put in that the furnace is a 75000 btu unit. 20 years old. The tanked water heater I chose, is 40000 btu.
I was looking at the pipe table last night but couldn't make sense of it.They were showing the numbers in CFM. Unless I was looking at the wrong table. But I'll go back & search and calculate it, now that you've told me how to do it. Thank you again.

#### Phog

##### Active Member
Thank you for the replies. Forgot to put in that the furnace is a 75000 btu unit. 20 years old. The tanked water heater I chose, is 40000 btu.
I was looking at the pipe table last night but couldn't make sense of it.They were showing the numbers in CFM. Unless I was looking at the wrong table. But I'll go back & search and calculate it, now that you've told me how to do it. Thank you again.

Ah yes. They also do have tables that have thousands of btu/hr.

https://s3.amazonaws.com/ao-kitchens/2016/12/14030910/21eb7_0.jpg

Based on those burner sizes you gave, you definitely don't need to worry about the gas furnace being starved by adding another 40,000 btu/hr appliance. And 1/2" should be fine for the new 40' water heater line.

However if you ever decide to go with a bigger high recovery water heater in the future, or want to add another appliance such as a gas clothes dryer onto this new branch, 1/2" wouldn't be big enough. So it might make sense to do it in 3/4" pipe anyway. It's a little more expensive but not really that much... Perhaps \$50 extra parts cost for your 40' length (if you're doing it in black iron).

Finally it's a good idea to install one or more tees with extra (capped off) ports, to leave space for any future expansion needs that might arise.

#### logwolf

##### New Member
That link is exactly what I was looking at.
So, if I add 3/4" line instead of 1/2", it will not pull too much from my furnace? You're right, I should add an extra T or two for possible future connections.

#### Phog

##### Active Member
You can always oversize the lines, it won't hurt anything. Undersizing is what you need to be careful to avoid. Also it's important to follow code and get permits. Gas plumbing is extremely dangerous if done incorrectly.

#### Dj2

All gas pipe modifications must be permitted, pass a 24 hr leak test and signed off by the city inspector.

#### Sylvan

##### Still learning
I have never ran a 1/2" natural gas line always a min of 3/4 NYC requires the min gas cock to be 3/4" .

At the appliance we reduce the size using a 3/4 x 1/2 or 3/8 reducing coupling

Learning every day

#### Bcarlson78248

##### Member
If you are running gas lines its best to look at the overall needs of the house. When they installed my new gas boiler they were able to T into the 3/4" line for the gas water heater because it was large enough. When they set up the connection for my gas dryer they were able to T into the 3/4" line for the gas stove. All this was inspected as part of a basement renovation, so it was relatively simple to get it installed an approved before walls were close in.

Bruce

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