lweford
I recently purchased a used 20kw Generac air cooled unit. This unit is going to be used on natural gas. I am wanting to replace the flex hose with the newer stainless flex hose. I am seeing 3/4 and 1/2” hoses. The original hose is 1/2” and the female port on the inlet at generator is 1/2”. Will the 1/2” stainless hose hose be okay? Keep in mind I will have 1-1/4” black pipe running all the way to the flex hose.
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78buckshot
If you can find a 3/4"CSS line with 1/2" fittings it would be better, or a 3/4 x 1/2 reducing coupler at the generator inlet and use the 3/4 CSS line, the less restriction you can provide the better, same with any shut-off valve you might be using - bigger is better.
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lweford
So I have a 1-1/4” full flow shutoff valve. Every part of my 15’ gas run is 1-1/4” except for the 1-1/4” x 1/2” reducer and the flex hose. So I will have approximately 12-15 inches(flex hose and short nipple) of 1/2” gas line in my run and that will be right at the generator. I just don’t want any fuel issues.
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Birken Vogt
I've seen some pretty awful installations like 1/2" pipe running 50 feet which goes negative when it starts but the thing still works like that.  A few feet of 1/2 is not going to bother anything.  If it has a 1/2" inlet then it is meant to run like that.
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lweford
Appreciate the info. Just want to have things done right the first time.
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78buckshot
Looks like your good to go.
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Brian Baughman
Everything will be fine, just be sure to follow the installation instructions on the Dormont label.
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restosud
lweford wrote:
I recently purchased a used 20kw Generac air cooled unit. This unit is going to be used on natural gas. I am wanting to replace the flex hose with the newer stainless flex hose. I am seeing 3/4 and 1/2” hoses. The original hose is 1/2” and the female port on the inlet at generator is 1/2”. Will the 1/2” stainless hose hose be okay? Keep in mind I will have 1-1/4” black pipe running all the way to the flex hose.


re check the inlet port on generator.the thread should be 3/4"npt and 20kw's came with a 3/4" threaded black rubber flex hose
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lweford
Yeah I have checked again and it is 1/2" npt. I even had the fuel system recall done after I purchased it, which essentially is a totally new fuel system, and the inlet on the new system is 1/2" npt as well. I don't know. The dealer said 1/2" is enough and a couple of you guys said it would be fine as well so I am gonna go with it. All I know is my Rinnai on demand water heater has a 3/4" inlet for NG and it's only 199,999 BTU. 
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78buckshot
Whatever the engineer deemed adequate for each application, as long as you have followed the piping charts for the unit you'll be good.
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restosud
can you post a pic of the inlet and the model and serial number?
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lweford
Thanks Geoff Z. Looks like I will be contacting the dealer who did the recall. Looks like they installed the wrong inlet. I don't have a shot of the inlet right now.  
IMG_0605.jpeg 
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Geoff Z
I looked up your installation manual using your serial number. Your model is a 1/2” inlet. The other was from today’s installation manual. I wouldn’t have thought that would change. Forgive the misinformation. 
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lweford
Appreciate you doing that. Glad to figure it out before I called them in the tomorrow morning. 🙂 What I did was put a 1/2npt x 2" nipple in the inlet with a 3/4npt x 1/2npt reducer immediately afterwards. Now I can use a new steel 3/4 flex hose to my run of 1-1/4npt.
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Mike03
Ideally you should have used half inch shoulder nip into a 3/4"x1/2" black tee for your sediment trap. And came off the top of tee with 3/4" 90 and you 3/4" flex hose.
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Geoff Z
Yes that generator does not have a built in sediment trap. Whereas today's air cooled models do.
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lweford
I can always put one right next to the input of the generator but I do have a sediment trap about 5’ upstream in the 1-1/4” section of my run.
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Wireform
lweford wrote:
I can always put one right next to the input of the generator but I do have a sediment trap about 5’ upstream in the 1-1/4” section of my run.
Would love to see a picture of that trap as half the time they don't work in the configuration they're installed. It's not a magic kind of thing that the sediment falls into the drip leg so what you have there may not be doing the job
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