Natural Gas Requirements: Generator and Water Heater Together

[Mitchell-DIY-Guy]

This is a question for our pros with natural gas line experience. First be reminded that a licensed plumber will be called in to do the work here. So my question is to help understand and follow what he may propose.

I have a multiple pressure natural gas system in the home here. I have what looks like a ⅝" or so (I'm guessing) 2 PSI main line coming in from the meter. It goes to a split manifold with regulator in the middle, where several smaller lines emerge at both 1 PSI and 2 PSI. Every device has a regulator near the termination point. So, right before the stub out for my gas grill, there's a regulator. There's a regulator at the stub out in the garage that the water heater is connected to.

I want to have a stub out on the side of the house to feed a natural gas powered generator. The manufacturer of the generator gave these wide specifications (with no BTUs given) of ".2-.4 PSI, 6-12 inches WC". Seems to me that is a massively wide range of gas power. The ideal situation is to put a TEE before the water heater regulator, run a pipe through the garage wall, and stub out. I need to ensure that this gas line before the regulator can deliver enough gas for the generator and the water heater, a standard 50 gallon, 40K BTU model. I don't know what the pressure or WC requirements are for a 40K BTU water heater.

I am assuming any plumber qualified in gas can measure the gas available at the wall in the garage, and affix the proper regulators to do just that? Maybe it means changing the connection point of that line from a 1PSI to 2PSI source, as both are available.

Am I missing anything in my understanding?

 

[Geofd]

You need to know the total btus in the house
By adding each fixture btu rating that will tell you what size has main to bring in from the street, your gonna get 1/2 psi in your house
At least I'm mass any thing over that is considered high pressure your generator will be a home run teeing off the main before any fixture

 

[Twowaxhack]

Post a link to the generator.

You’ll most likely need to run a dedicated 2lb line from the meter to the generator location. I’m not sure what size yet until you can give me more generator info and how far the meter is away from the generator location. That’s the short answer.

 

[Mitchell-DIY-Guy]

Post a link to the generator.

You’ll most likely need to run a dedicated 2lb line from the meter to the generator location. I’m not sure what size yet until you can give me more generator info and how far the meter is away from the generator location. That’s the short answer.

https://westinghouse.com/products/wgen10500tfc-tri-fuel-with-co-sensor

I should have mentioned this is a "portable, tri-fuel" model, not a built in.
I'm guessing that the ideal generator location would be about 50' from the meter.
Will only be run in emergency situations. Either propane or NG. I don't keep gasoline around.
I'm a bit surprised they mention nothing about the requirements when running on NG.
The company was a bit quick to tell me .2-.4 PSI, 6-12 inches WC but also was quite clear they won't provide the BTU consumption. Jeez, if anyone would know, they would. Unit comes with a long NG gas hose, identical to one for my grill, along with a similar hose for direct hookup to a propane tank.

@Geofd we do not have any .5 PSI lines in the home. All the piping is copper tube of varying sizes, and everything is either 2 PSI or 1 PSI. Then, at each fixture there's a gas pressure regulator taking the pressure down from either 1 or 2, probably to the .5 that most items are looking for. I count five regulators inside my home; one at the manifold, one each for the two furnaces, one for the water heater, one for the gas grill outside. Gas main into the home is 2 PSI.

Local plumber coming to look tomorrow. Trying to avoid a home run gas line since there's no way to get the gas where I want it without way too much work.

Thanks--

 

[Twowaxhack]

If you can tap into a 5/8” OD copper tube (1/2” ID) @2psi then it’ll work fine. Just be sure to install your pressure regulator close to the generator. This way you’ll have just a short piece of low pressure piping between the generator and the regulator that drops you from 2psi to around 8” W.C.

You’ll likely be able to use other gas appliances at the same time. A 5/8” copper tube @2psi will carry a lot of gas but how much would depend on length of pipe and how many fittings are in the line.

A 5/8” copper tube @2psi will run approximately (keyword) 300,000 btu with a 60’ developed run of tubing.

I’m figuring the max btu your generator would use would around 180,000 btu. But could be less, like around 150,000 at max load.

 

[Twowaxhack]

I think I was being generous with the btu estimates of the generator.

The manufacturer needs to step their game up and give the btu consumption of their product. Telling you the pressure is only giving you 1/2 the info, if that. Most things do run on between 6”-12” wc or close to it.

 

[Mitchell-DIY-Guy]

I think I was being generous with the btu estimates of the generator.

The manufacturer needs to step their game up and give the btu consumption of their product. Telling you the pressure is only giving you 1/2 the info, if that. Most things do run on between 6”-12” wc or close to it.

I agree.
It’s a Tri-fuel model.

If you want to run gasoline, fill the attached tank. They tell you what kind of gas to use and the approximate consumption per hour at various loads.

For propane, they give you the hose and even suggest how long various sized tanks may last at various loads.

For NG? Nada. Zip. Zilch. They give you the hose—but not a word beyond that.

We’ll see what my friendly local plumber friend says today.

 

[Mitchell-DIY-Guy]

I agree.
It’s a Tri-fuel model.

If you want to run gasoline, fill the attached tank. They tell you what kind of gas to use and the approximate consumption per hour at various loads.

For propane, they give you the hose and even suggest how long various sized tanks may last at various loads.

For NG? Nada. Zip. Zilch. They give you the hose—but not a word beyond that.

We’ll see what my friendly local plumber friend says today.

When in doubt...seek answers from competitors?

Since Westinghouse is devoid of any information whatsoever on use of their tri-fuel model with NG, (even that WC rating isn't published, you have to ask!) I went to the Generac website. They have a "whole house" built in standby generator with similar specifications. Here's the model:

https://www.generac.com/residential...ous/standby-generator-10kw-wifi-enabled-7171/

In their specification sheet, they are pretty clear:

101 ft3 per hour at 50% load on NG
127 ft3 per hour at 100% load on NG
Fuel pipe must be sized for full load. Required fuel pressure to generator fuel inlet at all load ranges, 3.5-7.0 WC for NG.
For BTU content, multiply ft3/hr x 1,000 for NG.

Also went to the Firman website. Firman makes similar portable models in varying sizes.
Firman T09371 11600W
86 ft3 per hour at 50% load on NG
126.7 ft3 per hour at 100% load on NG
7-11 WC pressure

FWIW, the NG hose included with the Westinghouse is ½", with ½" fittings, and a .5 PSI rating for outdoor use only.

 

[Twowaxhack]

When in doubt...seek answers from competitors?

Since Westinghouse is devoid of any information whatsoever on use of their tri-fuel model with NG, (even that WC rating isn't published, you have to ask!) I went to the Generac website. They have a "whole house" built in standby generator with similar specifications. Here's the model:

https://www.generac.com/residential...ous/standby-generator-10kw-wifi-enabled-7171/

In their specification sheet, they are pretty clear:

101 ft3 per hour at 50% load on NG
127 ft3 per hour at 100% load on NG
Fuel pipe must be sized for full load. Required fuel pressure to generator fuel inlet at all load ranges, 3.5-7.0 WC for NG.
For BTU content, multiply ft3/hr x 1,000 for NG.

Also went to the Firman website. Firman makes similar portable models in varying sizes.
Firman T09371 11600W
86 ft3 per hour at 50% load on NG
126.7 ft3 per hour at 100% load on NG
7-11 WC pressure

FWIW, the NG hose included with the Westinghouse is ½", with ½" fittings, and a .5 PSI rating for outdoor use only.

That’s what I did. It’ll run around 150,000 BTU’s. The 5/8” 2lb line will work if it’s a reasonable developed length from the meter.

 

[Mitchell-DIY-Guy]

So the first plumber I called apparently was all talk...despite all his years of experience either was unwilling or forgot his gas line work. Called the morning of his appointment, and then begged off when I described what I wanted. Maybe math wasn't his thing.

The second plumber came today, and he's got a plan, to quote the fictional character, Col. John "Hannibal" Smith from "The A Team"--I love it when a plan comes together.

He looked at what I had, ran some measurements and calculations, and will run a new home run pipe parallel to my water heater gas line (which is also home run back to the meter). This will exit in my garage as was my plan, then exit out the side of the garage wall to a stub out. QR on the stub out to power the generator. Didn't seem to have any issues. Just needs to ensure the right pipe sizes. He'll use soft copper in my gorgeous crawl space, and iron outside the wall in the garage and outside. He's got the charts and the calculations and all the BTU requirements, with a +10% added for safety. He's done a lot of generator gas line installs.

Will post photos. Work to be done the week after next.

 

[Mitchell-DIY-Guy]

So the work was completed today. I have a gas line stub-out on the side of my home for use in emergency situations with a tri-fuel generator.

The plumber I hired came for an estimate two weeks ago, took a bunch of measurements, pulled up his charts on his phone along with his calculator and made a mental plan and then provided an estimate.

Here's what he did: first, there was a small 3-port manifold of black pipe coming right off the gas meter inside the crawl space. Pressure here was 2 PSI. One port was used for the furnace upstairs, a ½" soft copper line. Another line was ⅝" soft copper and that ran to the other side of the house to another manifold where it had branches for nearly everything else in the home. The third line for the water heater (in the middle) was also a ½" soft copper pipe, running about 80' through the crawl space and out the garage wall. He removed that ½" line for the water heater starting at the meter, ran 50' of ⅝" towards the water heater, then branched off into two ½" lines each about 30' long. One was for the existing water heater, and the other for the new gas line for the generator. He made a small iron manifold out of ¾" iron pipe with a heavy duty regulator on it that took the pressure down to 7" WC. That's inside the crawl space.

He had calculated that at the split from ⅝" to 2 x ½", 50' from the gas meter, there was enough gas at 2 PSI for about 380K BTU. At the split, there's another 30' of ½" to go to the water heater which is 40K BTU. Then a parallel 30' of ½" for the generator which is 130K BTU.

Total plumber's labor time about 3.5 hours. Big parts were the 50' roll of copper tubing, the regulator, and some fittings.

 

[havasu]

I'd like to see some pics of the generator mounted.

 

[Mitchell-DIY-Guy]

I'd like to see some pics of the generator mounted.

As soon as I complete the work on my electrical panel, I'll get that done and post complete photos.
Remember this isn't a "mounted" permanent generator; it's a portable (or due to the weight I'd more likely call it "transportable") that will live in the garage, and only come out in need.

The gas line was brought near the electrical meter, and that's where the back-feed will occur. When attached and running, generator will sit on a pad where our trash cans are now, off the driveway on the side of the garage. We don't keep any gasoline around since we don't have any portable tools that use it. Thus the desire for a small unit that will operate off of propane of NG. You can use gasoline but we won't.

Shown in the photo is the backfeed interlock device. The generator will backfeed through a 50A breaker that can ONLY be turned on, when the main is turned off.
The next photo is the generator itself, though a stock photo. Last photo is the backfeed outlet, the same used for generators with RV campers, etc.

Step one was getting the generator. Step two was getting the gas line installed. Step three is the electrical panel work which I should get done this weekend.

 

[havasu]

My neighbor has a similar set up. He still uses his gas genny, but I also want to utilize NG, since my breaker panel and incoming NG is all in one area.

 

[Mitchell-DIY-Guy]

OK, so everything is finally installed and tested. Now I have a ready set up for quick connection of my backup generator when the power would go out for an extended time. This came to a head after the last hurricane Helene hit here, and we were w/o power for 18 hours.

Summary:
1. Gas Line. The gas line to the water heater came right off the meter, was ½" copper, and ran about 70' at 2 PSI. Plumber changed the first 50' of this to ⅝" copper, added a tee, and the last 20' remained the ½" for the water heater, and he ran more ½" to an outside wall in my crawl space. There, he added a ¾" regulator (because he likes the larger ones) there, and ran hard pipe outside and added a QR fitting. His calculations indicated I have plenty of gas available for the generator.
2. Electrical. I added a 50A breaker to the lower left corner of the panel, and a code-compliant mechanical interlock. The interlock prevents the breaker, used to backfeed, from being ON when the mains is ON. Mains have to be OFF for the generator feed to be on. Don't want to kill the lineman! (note: photo shows the original 30A breaker in place with interlock before I changed to the 50A)
3. Electrical Box Outside. This is a 50A unit with an LED indicator on it. If there's power in the box either from the front or back, it lights. Typical use is in RV feeds.

See photos for the work, and when all is connected.

 

[havasu]

Awesome. i envy you. I'm not a plumber, but that water heater strapping used for the gas lines look wonky to me. May I ask how you decided what you would power up, and why?

When I run my generator, I plug in the refrigerator, my satellite dish, my cable box and my primary TV, and also my electric recliner. This is about all the juice I have in my 3500 watt gas generator.

 

[Mitchell-DIY-Guy]

Awesome. i envy you. I'm not a plumber, but that water heater strapping used for the gas lines look wonky to me. May I ask how you decided what you would power up, and why?

When I run my generator, I plug in the refrigerator, my satellite dish, my cable box and my primary TV, and also my electric recliner. This is about all the juice I have in my 3500 watt gas generator.

The generator is fully capable of running the entire house with the exception of air-conditioning. To me it was all or nothing… but I did not want a permanently installed generator because it would cost $15,000, and too many rules and regulations about placement when the houses are so tight together here.

Pipe hanging seems to be a thing that people comment on when I post pictures of things in my house! Apparently everybody does it a little differently and nobody here likes the way anything is done in my home. However, I can tell you that everything has been done by a licensed plumber, and has passed inspection. So I guess I just shrug my shoulders.