What Kind Of Gas Are We Talking About?
In this article we will talk about gas usage by generators – how much gas does a generator use. Before we start, remember that the term “gas” is ambiguous and basically we have three kinds of “gas” to think about.
For each one of these, we’ll find out how much gas is used by generators, and throw in a carbon emissions comparison too. If you just want the answer, here is a table that summarizes our analysis.
The table shows the fuel needed to power a standard house for one day or the amount of gas used in 1 hour. Read on to find out our methods.
|Gas used per day
(Typical house needs 30 kWh / day)
|Gas used in 1 hour
|2200 watt Portable
|7.41 kWh / gallon
|4.0 gallons (not peak output)
|Natural gas (gaseous)
|7000 watt Stand-by
|0.046 kWh / cu ft
|658 cu ft (not peak output)
|152 cu ft
|2500 watt Portable
|4.62 kWh / gallon
|6.5 gallons (not peak output)
Let’s Specify The Types Of Gas: Gasoline, Natural Gas And Propane
Ok so the three types of gas we’re going to consider are gasoline, natural gas, and propane. One of the important things to note is that the way we measure these three types of gas is different.
The first two types, gasoline and propane, are liquid (propane is also known as “liquified petroleum gas” or LPG) so the unit of measurement is the gallon. And each gallon is convertible to a BTU or kWh. See the table below.
|Measurement for volume/mass
|1 cu ft or 1 therm
|Propane also known as LPG (liquid)
The second type, natural gas is truly a gas. Even if it were “liquified natural gas” before, by the time it gets to your home, its going to be in gaseous state. Natural gas is mostly “methane.”
For readers with chemistry background, methane is a smaller, more symmetric molecule. It requires lower temperatures or higher pressures to liquify.
The pressure to liquify would be so high that common metal tanks used in a home are too weak. Therefore, natural gas gets to your home through underground pipes.
The units of measurement for natural gas is the cubic feet (cu ft) or “therms” or “BTUs” (see table above).
A final note from us regarding the table: the two liquid fuels correspond to use in portable generators, whereas the gaseous fuel is used in stand-by generators. There are exceptions! It’s possible to get a portable that uses natural gas or have a stand-by that uses propane.
Carbon Emissions: Gasoline Is Highest, Natural Gas Lowest, And Propane Is In Between
At ShrinkthatFootprint we’re not big fans of these energy sources for emergency electricity because that’s what we’re about – we’re looking for carbon free sources of energy.
To go carbon free, we advocate switching to solar or getting your electricity from a clean grid. Even the cleanest fossil fuel has carbon emissions that are an order of magnitude higher.
However, given that these generators are used only in an emergency, we understand that their use will be limited. So lets we compare these three using the carbon emissions per usable unit of energy as the metric.
In prior comparisons we used IPCC reported figures. Unfortunately they don’t carry propane carbon factors. Worse, comparing the US EIA factors and IPCC factors show the two are estimated in different ways.
Take a look at the carbon factor of coal in IPCC (1000 g / kWh) vs in EIA (325 g / kWh). To have high consistency, we use only a single source, the EIA.
|Emissions (g CO2 / kWh)
To make this easier to compare and more consistent with our website, we converted everything to grams and kWh. Just looking at this table, we conclude that their carbon output per kilowatthour is pretty similar.
Natural gas has the lowest carbon emissions at 177 g CO2 / kWh; gasoline has the highest carbon emissions at 240 g CO2 / kWh; propane is in between at 211 g CO2 / kWh.
Let’s Specify The Types Of Generators: Portable Vs Stand-By (Or Fixed)
Take a look at your generator of interest and find out its power output rating – measured in wattage or watts. This is the amount of energy it puts out per unit time.
High power means a lot of energy comes out in a short time. If you want a “standard” one, 2000 watts is a good power to start. A smaller generator is 1000 watts and a powerful one is 5000 watts.
For comparison, a good sized efficient fridge uses 1.5 kWh (or 1500 watt hours) of energy per day, which translates to a constant output of 62 watts over 24 hours (62 watts times 24 hours = 1500 watt hours).
A standard 2000 watt generator running at half load (1000 watts) easily supplies the 62 watts, with 1000-62 = 938 watts left over for other tasks.
Other appliances that are high power? Consider the coffee maker, a laptop during recharge, and an air conditioner. All will add to the load noticeably. Sizing a generator correctly means accounting for all the simultaneous uses that add to the load.
Let’s Specify The Amount Of Power Needed For A Specified Time
Gas used in 1 hour
To compute the gas used in 1 hour, we simply specify the energy output achieved after 1 hour of peak operating time which is given by the wattage times 1 hour.
For example a 2200 watt generator in 1 hour will generate 2.2 kWh. Then we divided this by the efficiency to get the number of gallons or cubic feet of gas needed.
For example for the Honda the efficiency is 7.41 kWh / gallon, so 2.2 divided by 7.41 yields 0.30 gallons, about a third of a gallon.
Gas used by a household in 1 day
It makes a lot of sense to ask how much gas is needed for a given generator power and the amount of electricity needed by one home for one day.
From our own analysis on average household electricity consumption, a typical home in the US uses 30 kWh per day which is about the same as 102,000 BTU. The question is the amount of the gas (natural gas, gasoline or propane) needed to hit this figure of 30 kWh.
Also note that you don’t need to run it at peak output, so the amount of gas needed in 1 hour at peak is less relevant. The reason is that the house has a load spread throughout 24 hours which is not the same as the peak power of the generator.
For example, to hit the target at full load of 2200 watts, the generator has to run 13.6 hours. How much gas (gasoline, natural gas, propane) is needed to run 13.6 hours? One could also run the generator at half load for 27.2 hours.
For either calculation, these numbers speak to the “efficiency factor”: the amount of gas needed to generate a certain energy output.
Case 1: 2200 watt gasoline generator to power a standard house at 30 kWh / day (100K BTU)
A good case study is the Honda 2200 watt generator, famous for its low noise. At full load load, a 2200-watt generator will burn 0.95 gallons of gasoline in 3.2 hours at its highest load 2200 watts.
That means the machine is supplying 7.040 kWh over 3.2 hours. The efficiency factor based on these is then 0.95 gallons of gasoline per 7.040 kWh. Correspondingly, the time to burn through this volume of gasoline is 3.2 hours per 0.95 gallons of gasoline.
To generate 30 kWh / day, we multiply 30 kWh by the conversion factor, which is 0.95 gallons of gasoline divided by 7.040 kWh, and that multiplication gives 4.0 gallons of gasoline
Final calculation: 4.0 gallons of gasoline are needed to power a house needing 30 kWh / day with the 2200 watt gasoline generator
Case 2: 2500 watt propane generator to power a standard house at 30 kWh / day (100K BTU)
A good case study for this is the Champion 2500 portable propane inverter generator. According to its specs, we estimate at full load it’d run 8.5 hours using up a 20 pound / 4.6 gallon propane tank.
The conversion then is 4.6 gallons of propane per 21.25 kWh. To reach 30 kWh, we would need 6.49 gallons of propane.
Final calculation: 6.5 gallons of propane are needed to power a house needing 30 kWh / day with the 2500 watt propane generator.
Case 3: Generac natural gas stand-by 7000 VA (7000 watt) to power a standard house at 30 kWh / day (100K BTU)
For the stand-bys, the draw on the natural gas hook-up means we need to calculate the rate of gas usage in cubic ft. The specs for this Generac model are given here.
For operating at 7 kWh for 1 hour, it draws 153 cu ft of natural gas. Running for merely 4.3 hours will burn 658 cu ft of natural gas to generate the total 30 kWh energy needed for one day.
At this point you might ask what’s the cost of 653 cu ft of natural gas? This is because you rarely measure the volume of natural gas used.
For the US, natural gas prices in 2022 are relatively low at about $12 per 1000 cu ft. This means powering a 30 kWh / day house with natural gas-derived electricity costs $7.89.
For the UK, natural gas prices spiked as with the rest of Europe due to the Russia-Ukraine conflict. As of the writing of this article, according to Trading Economics prices are $4.84 per therm (100 cu ft).
This would price the natural gas at about $31 to power the house for one day. This is 4-5 times higher compared to the US, consistent with historical trends of natural gas prices.
Final calculation: 658 cu ft of natural gas is needed to power a house needing 30 kWh / day with the 7000 watt Generac stand-by generator.
Municipal Grids Vs Generators
The most common electricity source for a house is from the municipal grid. The electricity first emerges at a source: e.g. a hydro power dam, wind turbines, natural gas furnaces.
That electricity travels from the source through utility lines. At the end, it reaches your home. A portable generator, in comparison, is a tiny device about the size of a cooler box or cabinet.
People put it outside the house, and there it converts fuel to electricity for the home. Unlike the grid energy, its fuel is a local source. That source? You can guess easily: gas. And like we mentioned above, there are three types of gas.
Interesting types of generators
How much gas a generator uses per hour is relative to the kind of generator you get. You’ll need a model that gives you control over your load and consumption, as various designs necessitate various fuels. The most popular types of generators include:
Standby generators are installed to guarantee power in the event of a outage. In most cases, it’s powerful enough to keep your home running for hours to days because they draw from a gas hook up to an inexhaustible source.
If you prefer to travel, then you have probably thought about purchasing a portable generator because of its small size, portability, and ease of use. Powering anything from laptops to air conditioners, all depends on the size of generator you get.
Portable generators are not suited for homes. You can see from the fuel requirements above you’ll be swapping out fuel tanks constantly.
The most compact choice is an inverter generator, which is ideal for running sensitive devices. These devices use the fuel to generate DC power that is then converted to AC.
If you’re in the market for a generator and want the most flexibility, a tri-fuel unit is your best bet. These power plants can be run on a variety of fuels, including the ones they are named after: natural gas, liquid propane, and gasoline.
Your current gas-powered generator can be converted into a tri-fuel model with the help of a readily available kit. There is also the possibility of using a generator that runs on both gasoline and diesel.
The fuel type of the generator you choose has a significant bearing on the amount of fuel used.
Although natural gas is considered a greener alternative to diesel, it is probably the most environmentally friendly choice available.
If your home already has natural gas lines installed, you have one of the key reasons to think about getting a generator that runs on natural gas. Without these wires, connecting the generator to serve as a backup power source would be physically impossible.
You are most likely to make an initial investment in one of these gasoline-powered generators because gasoline is one of the fuels that are most readily available.
However, because they require constant refueling, they are not just among the least expensive generators available but also the most inconvenient. It is also essential to keep in mind that during times of emergency, gasoline will be one of the fuels that are most difficult to locate.
Similar to gasoline, propane is easily accessible and has many potential uses. It’s a common choice for standby generators, particularly in places without access to natural gas connections.
For those who want to get into the nitty-gritty, homes in rural locations that frequently experience power outages can profit from installing a propane generator because propane is easy to find in remote areas.
Propane is another reliable fuel option for large generators with their often much larger tanks.
A generator that contains 500 liters of propane, for instance, may provide electricity to a home for a week. Most of these machines can hold up to a thousand gallons of fuel, but they can use up to three gallons an hour.
Regarding the consumption of fuel, the load is the final significant issue to take into consideration. The load is the number of electronic devices and/or home appliances that are connected to the generator and drawing electricity from it.
A modest load would be something like carrying about personal electronics, whereas a heavy burden would be something like moving an entire house. You must give some thought to what you want to be able to operate if there is a power outage.
If you look at advertisements for generators, you’ll note that they almost always present figures based on a load that’s fifty percent of its capacity.
If you’ll utilize more than half the device’s power, consider its maximum power consumption.
You Might Like: What is the Greenest Source of Electricity?
How Many Gallons Of Gas Does A Generator Hold?
There will be a significant difference in the capacity of the fuel tank between the various models and manufacturers of generators.
The fuel tanks of smaller generators, such as those that have a power output of 2,000 watts or fewer, can carry anything from one gallon to four gallons of fuel.
The fuel tanks of larger standby generators can carry as much as one hundred gallons of fuel.
How Often Should I Refuel My Generator?
How often you need to refuel your generator is going to depend on how much you use it. If you only use it occasionally, you might be able to get away with refueling it once a month, once a year.
However, if you use it regularly, you’ll need to refuel it more often. Unfortunately fuel sources like propane gas tanks don’t have internal gauges.
Gasoline Degrades – Be Prepared To Add A Stabilizer Or Replace It In 30 Days
An incredible inconvenience of gasoline is that it degrades over time. It’s not something that you want to leave sitting in your generator’s tank for too long. You have two choices.
Either you empty the fuel tank and run the engine until it runs out of gas. This will help to prevent any damage to the engine that could be caused by old gasoline. Or you add a fuel stabilizer to prevent evaporation and build up of residue that comes from the degradation.
The Bottom Line
As you can see, there are a lot of factors to consider when trying to determine how much gas a generator uses. The size of the fuel tank, the load on the generator, and how often you use it will all play a role in how much gas your generator consumes.
Keep these things in mind when you’re choosing a generator and you’ll be sure to get one that meets your needs.