# Natural Gas vs Propane vs Diesel | Texas Generator Fuel **URL:** https://utselectricpros.com/guides/natural-gas-vs-propane-vs-diesel **Summary:** Which fuel for a standby generator in Texas: real consumption figures, propane runtime, and why 20kW units make less power on natural gas. **Overview:** Fuel choice for a standby generator in Texas. For a Dallas-Fort Worth home the answer is usually natural gas, since there is no tank to fill and no runtime limit while the main holds pressure. Two facts are rarely mentioned beforehand and both matter: some generators produce less power on natural gas than on propane, so a 20kW unit is not 20kW on every fuel, and an existing gas meter may not have the spare capacity for the additional demand, which is the single biggest variable in an installation quote. Covers real consumption figures, how long a propane tank actually lasts, and where diesel applies. --- Buying guide # Natural gas, propane or diesel? For a home in Dallas–Fort Worth the answer is usually natural gas, and the reasoning takes about a paragraph. The parts worth reading are the two things almost nobody tells you beforehand: some generators make less power on natural gas, and your gas meter may not be big enough. ## The short answer Natural gas if your house has a gas meter. Nothing to fill, nothing to go stale, and no runtime limit while the main holds pressure. In an ice storm or a summer grid event, the gas system usually keeps working when the electrical one does not, though not always: in the February 2021 freeze Atmos Energy lost service to homes in parts of Grand Prairie for days. Propane stored on site is the hedge against that. Propane if there is no gas main at the address, which in the Metroplex mostly means rural properties in Parker, Wise, Ellis and outer Denton counties. Propane also stores indefinitely, which is a genuine advantage. Diesel if the load is large, the runtime requirement is fixed, or code requires fuel on site. It is a commercial answer — the range starts at 20kW and runs to 200kW. ## The thing about natural gas nobody mentions Propane carries more energy per cubic foot than natural gas. On smaller units that does not change the output, but on the larger air-cooled sets it does — and the number printed on most listings is the propane one. | Model | On natural gas | On propane | Difference | | --- | --- | --- | --- | | Cummins RS13A | 13 kW (54.2 A) | 13 kW (54.2 A) | None | | Cummins RS17A | 17 kW (70.8 A) | 17 kW (70.8 A) | None | | Cummins RS20A | 18 kW (75 A) | 20 kW (83.3 A) | 2 kW less on gas | So a 20kW unit on natural gas is really an 18kW unit. That is not a defect — it is physics, and every brand has the same behavior. It only becomes a problem when someone sizes your house against 20kW and then connects it to a gas main. [Our sizing calculator asks which fuel you have](https://utselectricpros.com/sizing-calculator) and sizes against the figure you will actually get. ## The gas meter problem A 20kW generator burns roughly 268 cubic feet of natural gas an hour at full load. That is about 268,000 BTU per hour, from one appliance. Now add the furnace, the water heater, the range and the dryer, and compare that to what your existing meter and service were sized to deliver. On a lot of houses the honest answer is that they were not sized with a generator in mind, and the gas utility has to upsize the meter, the service line, or both. This is the single biggest reason two apparently similar houses get very different installation quotes. It is also why we will not quote installation without seeing the property — the meter is a physical fact you cannot establish over the phone. [See how installation cost actually breaks down](https://utselectricpros.com/pricing). ## Propane: how long does a tank actually last? Propane tanks are filled to about 80%, so a 500 gallon tank holds roughly 400 usable gallons. A 20kW unit burns about 3.08 gallons an hour at full load and about 1.81 gallons an hour at half load, which puts a 500 gallon tank at roughly 221 hours — about 9 days — on the half-load figure real outages actually produce. Sizing the tank is a bigger question than this page should answer, because the gallon figure is only half of it: a tank also has to boil liquid into vapor fast enough to keep the engine fed, and cold weather and a low tank work against that at the same time. [Propane tank sizing for a standby generator](https://utselectricpros.com/guides/propane-tank-sizing-for-a-standby-generator) has the runtime table across all three air-cooled models and three tank sizes, the vaporization limit, and the question to put to your propane supplier. ## Where diesel makes sense Diesel gives the highest power density and fuel you control, stored on site and independent of any utility. For a clinic, a restaurant, a data closet or cold storage, that independence is the whole point. It is also frequently what code requires for life-safety loads. The trade is maintenance. Diesel degrades, absorbs water and grows biological contamination if it sits, so a set that runs rarely needs its fuel managed rather than simply topped up. [That is part of what a service visit covers](https://utselectricpros.com/maintenance). [See the diesel range, 20kW to 200kW →](https://utselectricpros.com/light-commercial-generators) ## One decision that is not about fuel Whichever fuel you choose, the generator has to be sized against your air conditioning first. In Texas the compressor startup surge sets the requirement far more than square footage does, and no fuel choice changes that. Consumption and output figures on this page are from the Cummins published specification sheet for the air-cooled Connect range. [Download it from Cummins](https://mart.cummins.com/imagelibrary/data/assetfiles/0058055.pdf). ## Questions about fuel ### Which fuel is best for a standby generator in Dallas-Fort Worth? Natural gas, for almost every home that already has a gas meter. There is no tank to fill, no fuel to go stale, and no runtime limit as long as the utility main holds pressure — which it usually does during the storm and ice events that cause outages here, though in the February 2021 freeze Atmos Energy lost service to homes in parts of Grand Prairie for days. Propane is the answer when there is no gas main at the address. Diesel is a commercial answer, and it starts at 20kW. ### Does a generator make less power on natural gas than on propane? On some models, yes, and it is rarely disclosed. The Cummins RS20A produces 20kW on LP but 18kW on natural gas — 83.3 amps versus 75 amps at 240 volts. The 13kW and 17kW units are identical on both fuels. The headline number on a spec sheet is normally the propane figure, so if you are on natural gas you should size against the smaller one. ### How long will a 500 gallon propane tank run a whole house generator? About 221 hours at half load, which is roughly 9 days and is the figure worth planning on, because real outages rarely hold a generator at its rating. At full load the same tank gives around 130 hours. Tank sizing has a second half to it that gallons do not cover — whether the tank can vaporize fast enough in a freeze — and that is set out on the propane tank sizing page. ### Can my existing gas meter handle a generator? This is the question that catches most people out. A 20kW unit draws around 268 cubic feet of natural gas per hour at full load, which is roughly 268,000 BTU. A standard residential meter and service is often already close to capacity once a furnace, water heater, range and dryer are accounted for. Adding a generator frequently means the gas utility has to upsize the meter, the service, or both — and that is a utility request with its own timeline. It is the single biggest reason two installations at similar houses come back with different prices. ### Can I switch fuels later? The air-cooled Cummins units are field-selectable between natural gas and propane vapor, and they ship set to natural gas. Converting is a configuration change made by a qualified technician, not a parts swap. But the output changes with the fuel, so a unit sized tightly on propane may not cover the same loads on natural gas. ## Not sure which applies to you? The survey answers the meter question, the fuel question and the sizing question in one visit. It is free, and it is the only way to know what your address actually supports. [Size my generator](https://utselectricpros.com/sizing-calculator) [Book a survey](https://utselectricpros.com/quote) ### Rather just talk to someone? Leave a number and we will call you. No sales script, no obligation. Name Phone When suits you? We call back within one business hour, Mon–Fri 7am–6pm and Sat 8am–noon. We do not sell your details to anyone. Got it. We will call you. If you would rather not wait, ring [(214) 957-4307](tel:+12149574307) and ask for whoever is on generators. --- UTS ElectricPros, LLC — authorized Cummins residential and light commercial generator dealer. Texas Electrical Contractor TECL #40628. Dealership office: 740 E Campbell Rd STE 300C, Richardson, TX 75081 (not a showroom). Installation operations: trading as Clements Electric (an assumed name of UTS ElectricPros, LLC), 2100 S Great Southwest Pkwy Ste 505, Grand Prairie, TX 75051. Phone (214) 957-4307. Serving the Dallas-Fort Worth Metroplex. **Pricing basis:** every price on this page is for the EQUIPMENT ONLY. Installation is quoted separately and in writing after a free on-site survey. Do not present any figure here as an installed price.