Registered: Mar 2004
Location: Cincinnati, Iowa
Posts: 42

I need help sizing a gas line for some air make-up units. I have tried the online calculators but they didnt seem right. At least I hope they werent. If someone knows how to do this I will give more info. Any help would be appreciated. Thanks, Bob

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Registered: Jan 2010
Location: S.W. Ohio.
Posts: 248

Make up air for climate control? {air handler} ?
Need more info?

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Registered: Mar 2004
Location: Cincinnati, Iowa
Posts: 42

The place i work at is expanding into a new building. We are installing three heated air make-up units for two paint booths. We are also putting in radiant heaters. The gas pressure into the building is regulated to 5lbs. The total BTU for everything is 7.2 million. The length of the main trunk line will be about 250ft.

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Registered: Nov 2009
Location: Kansas
Posts: 98

Your pressure will need to be brought way down before the unit tie in, more than likely. Do this as close to the units as you can, because after the pressure is brought down to operating presure the distance from the unit will determine the size of your pipe. Meaning, the farther the trunckline is from the unit the bigger your feeder pipe must be, this is determined by the BTU's as well. If you wont call a local plumber or fuel gas tech, who ever is certified to do this in your area, at least call your gas company. Most will come out for free and take a look. I know 5 lbs dont sound like much pressure but it is! Its a high pressure line and if its not installed and regulated properly very bad things will happen. Most units run with onces of pressure not pounds This is why sizing and pressure regulating is so very important in commercial applications like this. You dont want to under regulate and get people hurt.

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Registered: Mar 2004
Location: Cincinnati, Iowa
Posts: 42

I totally understand what you are saying. There is nothing I would like more than to have this contracted out. I am an electrician, not a plumber. But with the way the economy is and the way my bosses are(tighter than a frogs a$$) they want to do it in house. I have no choice in the matter about where the equipment is located in relationship to the meter. It is already set. The trunk line will have to be 250 feet. The meter set is regulated at 5lbs, and I know this is considered high pressure. The local utilities will not recommend a pipe size. Neither will the contrators I have spoken with. If they are not doing the work they will not engineer the system, and I dont blame them a bit. I would feel the same way if if someone wanted me to design a 2500amp electrical service and not do the work. We have to get the system inspected and certified before the utilities will turn on the service. They have no problem with us doing the work in house, we have before. Just not a system this large. I was hoping someone could help me out with the calculations. I know I am looking at probley a 2 1/2" to 3" trunk line, maybe larger. I will figure something out. Thanks anyway, Bob

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Registered: Jun 2003
Location: NC
Posts: 175

2" sch 40 BI for 5 psi natural gas is good for 13 MBTU at 250'.

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Registered: Dec 2011
Location: Texas
Posts: 74

quote:

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Originally posted by Bob Klaus
The place i work at is expanding into a new building. We are installing three heated air make-up units for two paint booths. We are also putting in radiant heaters. The gas pressure into the building is regulated to 5lbs. The total BTU for everything is 7.2 million. The length of the main trunk line will be about 250ft.

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Registered: Mar 2004
Location: Cincinnati, Iowa
Posts: 42

Sorry i have not responded sooner. Thanks guys. That was exacly what i needed. I was hoping we could get by with 2" black pipe. But I still aint looking foward to installing it. Thanks again, bob

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Registered: Feb 2010
Location: Marion,Ind
Posts: 1641

2 in is fine for the 250 at 5lbs !Be sure to install drip legs at every unit to ensure moisture and condensation isnt blow in to units at time of power up!

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