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Need help estimating usage cost for a whole house generator

Posted on 7/10/24 at 8:42 pm
Posted by Willie Stroker
Member since Sep 2008
14561 posts
Posted on 7/10/24 at 8:42 pm
Natural gas appears to be cheaper, but natural gas does not appear to be charged as kilowatt hours. Instead, I'm billed by a measure called centum cubic feet.

If my current electrical consumption is 50 kWh per day, how do I convert that to a consumption cost of a natural gas whole house stand-by generator where natural gas is measured by centum cubic feet?

The best tool I found just gave ccf estimates based on 4 tiers of load for each size generator. That is somewhat helpful, but not as precise as I would like.

What says the H&G?
Posted by jmon
Loisiana
Member since Oct 2010
9286 posts
Posted on 7/10/24 at 8:44 pm to
At least $30/day to run a whole home generator on natural gas.
Posted by Willie Stroker
Member since Sep 2008
14561 posts
Posted on 7/10/24 at 8:58 pm to
quote:


At least $30/day to run a whole home generator on natural gas.

For comparison purposes, what's that same home's cost per day on electricity?
Posted by cgrand
HAMMOND
Member since Oct 2009
43462 posts
Posted on 7/10/24 at 10:06 pm to
it will tell you on the cut sheet for the model generator you are looking at. For example a 22kw generac burns about 3 gal/hr of propane at load. Look up the specs on yours
Posted by Spankum
Miss-sippi
Member since Jan 2007
58594 posts
Posted on 7/10/24 at 10:43 pm to
quote:

centum cubic feet


1 CCF equals 100 cubic feet
Posted by Willie Stroker
Member since Sep 2008
14561 posts
Posted on 7/10/24 at 10:49 pm to
quote:

1 CCF equals 100 cubic feet
Thanks for fact sharing, but my Google Machine was on top of this one.
Posted by billjamin
Houston
Member since Jun 2019
15102 posts
Posted on 7/10/24 at 11:04 pm to
I’ll let you know when my bill comes it. Mines been running for 60 hrs and counting.
Posted by Dallaswho
Texas
Member since Dec 2023
2674 posts
Posted on 7/10/24 at 11:38 pm to
1mmbtu is 300kwh.
Guessing your residential prices are close to $10 for that much gas and $45 for that much electricity.
21% efficiency overall would be super optimistic though.
I think you’d optimally have electricity beatable if gas was $1 per ccf and electricity was over $0.20 per kWh but even that doesn’t account for wear/tear or maintenance.
Beatable doesn’t mean beat either. Still have to have generator and appliances ideally sized. My best guess is you’re running at 10-12% average efficiency and electricity costs would need to be over 30 cents to be beat by $1/ccf gas. This makes running gas approximately 2x electric price after subtracting the service charges that you’d pay anyway.
This post was edited on 7/11/24 at 11:23 am
Posted by TbrudLSU
Houma
Member since Oct 2012
13 posts
Posted on 7/11/24 at 6:58 am to
You can try to figure out cost with all kinds of formulas but during Ida my 22kw natural gas generator ran for 22 days. Our house is 4500 sq ft. 2 ACs. Ran whole house never skipped a beat. Bill was about 400 bucks. Real data.
Posted by slinger1317
Northshore
Member since Sep 2005
6551 posts
Posted on 7/11/24 at 7:24 am to
If you are worried about the cost to run the generator you are splitting hairs.

Natural gas is cheap and if the generator is running, you won't be using electricity. Trying to calculate the cost of the gas is pointless.

Having a whole house generator is a matter of convenience and peace of mind. If cost of gas is a concern, consider that it may run for more than 6 hours about once every 2-3 years in our area. 99% of your usage will be small power blinks/brief outages.

I have had one since 2019 and only twice has it run for more than a few hours.
This post was edited on 7/11/24 at 7:25 am
Posted by cgrand
HAMMOND
Member since Oct 2009
43462 posts
Posted on 7/11/24 at 7:27 am to
exactly

is anyone really concerned enough about the cost of gas when the power is out to not run the generator? That’s what it’s for

the cost of the generator and gear will never be recouped so you will be underwater on it forever. Let it run
Posted by Willie Stroker
Member since Sep 2008
14561 posts
Posted on 7/11/24 at 7:49 am to
quote:

If you are worried about the cost to run the generator you are splitting hairs.

Worry?

I’m just trying to do a more thorough cost/benefit analysis to an alternative.

Seems like it would be useful to know what to plan for during extended power outages, no?
Posted by southern686
Narnia
Member since Nov 2015
989 posts
Posted on 7/11/24 at 9:00 am to
quote:

Seems like it would be useful to know what to plan for during extended power outages, no?

It is useful. I just think you're trying to compare something that isn't comparable so to say.

quote:

If my current electrical consumption is 50 kWh per day, how do I convert that to a consumption cost of a natural gas whole house stand-by generator where natural gas is measured by centum cubic feet?

This is not directly proportional. You are charged by the kWh from the power provider. On utility power, as your load goes up, the meter spins faster. Load goes down, meter slows, no load meter stops. However, a generator runs at max RPM no matter the load you are pulling. That said, your gas meter is going to spin at a pretty much constant rate. Even if everything in the house is off, that generator is still running at max RPM and the gas meter is still spinning.
Sure, a large load such as kicking central air on will load the generator slightly and it may consume slightly more fuel but not enough to make a difference or worry about calculating.

That said.....
I have a 20Kw Generac on my home. It cost me roughly 20-24 dollars a day (24hours) to run. FWIW, when I'm on generator, my AC is normally turned way down like to 66 because I'm paying for the gas to run the generator anyway.


ETA:
Think of it this way. Your paying by the hour to run the generator, not really by the electrical consumption.
This post was edited on 7/11/24 at 9:06 am
Posted by ellunchboxo
Gtown
Member since Feb 2009
19134 posts
Posted on 7/11/24 at 9:05 am to
My gas bill was $250 more than normal when it ran for 6 straight days during Ida.

So around $40 a day
Posted by notsince98
KC, MO
Member since Oct 2012
20120 posts
Posted on 7/11/24 at 9:07 am to
easier to do this if you get the generator specs. Find consumption data and kW production data.
Posted by Willie Stroker
Member since Sep 2008
14561 posts
Posted on 7/11/24 at 9:08 am to
Awesome. That helps.
Posted by notsince98
KC, MO
Member since Oct 2012
20120 posts
Posted on 7/11/24 at 9:09 am to
quote:

However, a generator runs at max RPM no matter the load you are pulling.


The fuel consumption rate changes drastically with generator load. Idle fuel consumption is much lower than when running say at 75% load.
Posted by TheBoo
South to Louisiana
Member since Aug 2012
5138 posts
Posted on 7/11/24 at 9:10 am to
We lost power for 14 days after Ida. My neighbor has a 2800 sq ft house with a 22kw generator. two AC units. He said his gas bill came out to about $21 per day extra to run the generator.
Posted by Stexas
SWLA
Member since May 2013
6588 posts
Posted on 7/11/24 at 9:11 am to
quote:

I’m just trying to do a more thorough cost/benefit analysis to an alternative.

I think the issue you're trying to nail down isn't going to be as accurate as you're hoping for without more specifics from you.

Someone already offered to give you usage rates if you give them the model of generator/size you're talking about. The analogy that's coming to mind is asking what kind of gas mileage can I expect from a new vehicle. Are we talking about a diesel 1 ton all wheel drive dually or a hybrid prius?
Posted by poochie
Houma, la
Member since Apr 2007
6765 posts
Posted on 7/11/24 at 9:14 am to
Mine ran for 8 days for ida, looking at my notes, my bill was $274 for that month in 2021, 2019-2023 excluding 2021 averaged $35 so about $240 for those 8 days or $30/day. Generac 22kw.
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