Hey all. First post here but I've lurked on this forum here and there.
I think I'm overthinking this whole thing but I want to get some feedback from the pros. Perhaps scroll down to the bolded text to get at my point/question.
I'm looking to install a natural gas heater in my garage and trying to determine the proper gas line sizing for this run. I've been reading the IFGC but it goes in-depth(as it should) on a lot of other systems so I wanted to pose my question here and see if I'm understanding this correctly.
What I have and want to do:
- I have a 1/2" copper gas line running ~30' from the meter to a manifold at 2 psig. The line goes into a regulator that takes it down to 7-11" wc then that goes to a 100k furnace, 60k range @ 20' run with 3/8" copper, 35k dryer @ 25' run with 3/8" copper, and 50k water heater @ 8' run with 3/8" copper.
- I want to install a 60k unit heater that will be about 55' from the manifold.
-- I would tee off from the 1/2" line coming from the meter(before the regulator) and run it up to the unit heater and into a regulator that'll drop it down to 7" wc with a max inlet supply of 14" wc at the heater valve.
I first went to an engineeringtoolbox.com page that said 1/2" type L copper can only handle 41k btu on a 40' run. This is for less than 1.5 psi supply and allowable pressure drop of 0.5" wc. This didn't seem right to me because I've already got 1/2" copper from my meter to the furnace at a 30' run supplying a 100k furnace and more!
To muddy the waters even more, I read these (other) forum posts saying to use the engineeringtoolbox page and to use 3/4" to supply a 45k heater at 50'.
I refer to the tables in IFGC and it states that at less than 2 psi and 0.5" wc drop, a 40' run can supply 53 cfh(or MBH).
My belief is that if I'm running less than 1.5 psi or even the regulated 11" wc gas pressures, the tables are correct in limiting me to 41 or 53 MBH on that specific branch. But I WOULD be running 2 psi gas in a 1/2" copper line up until the regulator just before the unit heater, so this would not apply and I'd have to refer to the other tables for a 2 psi inlet pressure at 1 or 1.5 psi pressure drop. So 2 psi inlet pressure with an allowable pressure drop of 1 psi, at a 60' run on 1/2" K tubing allows me a capacity of 391 CFH up to the regulator.
Is my understanding all wonky? When I was getting quotes for the install, and before I decided to do this on my own, all of the hvac guys said they'd run a 1/2" copper line teed off from the meter supply line. It's these damn interweb forums filled with misinformed people offering advice that got me thinking. No offense to anyone in particular, I understand the human need to put in 2 pennies.
I think I'm overthinking this whole thing but I want to get some feedback from the pros. Perhaps scroll down to the bolded text to get at my point/question.
I'm looking to install a natural gas heater in my garage and trying to determine the proper gas line sizing for this run. I've been reading the IFGC but it goes in-depth(as it should) on a lot of other systems so I wanted to pose my question here and see if I'm understanding this correctly.
What I have and want to do:
- I have a 1/2" copper gas line running ~30' from the meter to a manifold at 2 psig. The line goes into a regulator that takes it down to 7-11" wc then that goes to a 100k furnace, 60k range @ 20' run with 3/8" copper, 35k dryer @ 25' run with 3/8" copper, and 50k water heater @ 8' run with 3/8" copper.
- I want to install a 60k unit heater that will be about 55' from the manifold.
-- I would tee off from the 1/2" line coming from the meter(before the regulator) and run it up to the unit heater and into a regulator that'll drop it down to 7" wc with a max inlet supply of 14" wc at the heater valve.
I first went to an engineeringtoolbox.com page that said 1/2" type L copper can only handle 41k btu on a 40' run. This is for less than 1.5 psi supply and allowable pressure drop of 0.5" wc. This didn't seem right to me because I've already got 1/2" copper from my meter to the furnace at a 30' run supplying a 100k furnace and more!
To muddy the waters even more, I read these (other) forum posts saying to use the engineeringtoolbox page and to use 3/4" to supply a 45k heater at 50'.
I refer to the tables in IFGC and it states that at less than 2 psi and 0.5" wc drop, a 40' run can supply 53 cfh(or MBH).
My belief is that if I'm running less than 1.5 psi or even the regulated 11" wc gas pressures, the tables are correct in limiting me to 41 or 53 MBH on that specific branch. But I WOULD be running 2 psi gas in a 1/2" copper line up until the regulator just before the unit heater, so this would not apply and I'd have to refer to the other tables for a 2 psi inlet pressure at 1 or 1.5 psi pressure drop. So 2 psi inlet pressure with an allowable pressure drop of 1 psi, at a 60' run on 1/2" K tubing allows me a capacity of 391 CFH up to the regulator.
Is my understanding all wonky? When I was getting quotes for the install, and before I decided to do this on my own, all of the hvac guys said they'd run a 1/2" copper line teed off from the meter supply line. It's these damn interweb forums filled with misinformed people offering advice that got me thinking. No offense to anyone in particular, I understand the human need to put in 2 pennies.
