Black pipe size question

[snowdust2]

I am running 200' of 1 1/4" gas line to my shop that will run a 75k btu Hot Dawg heater. Inside the shop I ran 1/2" black pipe about 30' to stub out where I'll connect the heater. I was looking at the manual and if I read it right I am real close to min CFH due to the 30' run of black pipe. Can someone with more knowledge than me take a look at the pic and see if they agree? I see it as I need 71.4 and I'll be at 73 if I am 30'. (I need to measure and may be closer to 35') Wondering if I should change it out to 3/4 before I drywall. Thanks!

 

[papp101]

What's the gas pressure inside your house at the source?

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[nmk_61802]

I see it as reading it correctly. FYI it's the total developed length of pipe, not linear. Every fitting adds approx. 3-5 ft. Depending on the complexity of the pipe you would probably be fine, 20 fittings probably not so much. Assuming less that 2PSI supply, I believe Ameren is at 7"WC (1/2 PSI)

That chart is also slightly conservative as it is only including around a .3-.5"WC pressure drop across the length. You may be able to push those numbers slightly and still achieve the min. supply pressure to the furnace (Probably 5"WC)

 

[SGKent]

often when someone measures they take a tape from point A to point B and it is whatever distance they come up with. But in reality the distance the pipe sees is W feet plus X up the wall, Y in the bends and Z from the wall to the device. Be sure your measurements include that.

 

[Leaflessshadetree]

I'd change it out, especially if there is a chance you get a larger heater or add another appliance in the future.

 

[rlitman]

I'd change it out, especially if there is a chance you get a larger heater or add another appliance in the future.

Ditto. Maybe put a tee in there for a grill?

 

[snowdust2]

I measured and it will be 40' from heater to the inlet coming into the garage. Only 4 90's so not a bunch of fittings but seems like I am pushing the limits. I don't know the pressure from the house. I haven't trenched that line yet and planned to get the gas company involved then.
I didn't realize there would be such a drop at just 40 feet so never even thought about going to the 3/4 pipe. Bummer to have to re-do it, but it is just framed now so easy to change out. Luckily this is a cheap mistake. Thanks for the feedback.

 

[nmk_61802]

I measured and it will be 40' from heater to the inlet coming into the garage. Only 4 90's so not a bunch of fittings but seems like I am pushing the limits. I don't know the pressure from the house. I haven't trenched that line yet and planned to get the gas company involved then.
I didn't realize there would be such a drop at just 40 feet so never even thought about going to the 3/4 pipe. Bummer to have to re-do it, but it is just framed now so easy to change out. Luckily this is a cheap mistake. Thanks for the feedback.

Don’t forget you can replace just a portion of the 1/2” and increase the capacity, if that is easier. About 15 ft would get there


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[snowdust2]

That's a good point. That would help.

 

[Jackfre]

ALWAYS oversized in the build. You simply do not know what the future holds. Build in capacity and flexibility. Also don’t use 90’s. Use tees and plugs. That way you can add easily.

 

[snowdust2]

Great idea on the T's. I'll use them instead when I switch it over.

 

[rlitman]

Don’t forget you can replace just a portion of the 1/2” and increase the capacity, if that is easier. About 15 ft would get there

Or maybe replace in 3/4" to the last elbow or so, keeping the end in 1/2".

Great idea on the T's. I'll use them instead when I switch it over.

I wouldn't go crazy with tees, as I prefer a system with as few joints as possible. But putting one in a place where you think you may use it will certainly make tapping into the system in the future easier. If you really plan to use it, you may as well put a valve in where you stub it out. Just be sure to cap/plug the valve.

 

[earlybirds]

I also ran 1-1/4 inch HDPE gas pipe 110feet to my shop to supply my 100,000 BTU Modine Hot Dawg heater. I then continued inside the shop with 60 feet of 1-1/4 inch black pipe to supply the heater and a gas grill.

I also added tees and plugs for future equipment(possibly a nat. gas powered generator).

 

[nadogail]

it is generally less expensive to build in more capacity than to add it later.

 

[Flat Thunder Channel]

I would run plastic tubing if possible. I had a black pipe installation rust away to nothing in only a couple years. It needed to be protected against corrosion with some kind of rust prevention. I still remember the dreadful day I had to re-trench a plastic line. You always learn on the first install how not to do it next time. Oops :/