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.