Key takeaways
- Generac's published ratings put the Guardian 24kW at 24,000 watts on propane and 21,000 watts on natural gas.
- A Generac 24kW suits larger homes, two air conditioning systems, or natural gas houses that are tight on a 22kW.
- On natural gas the 24kW gives 3,000 watts less than its propane rating, so size from 21,000 watts.
- Compared with the 22kW on natural gas, the 24kW adds 1,500 watts. Compared with the 26kW, it gives up 1,500.
What can a Generac 24kW run matters most to two kinds of homes: larger houses with more than one air conditioning system, and natural gas houses that come out tight on the 22kW. Generac's published ratings put the Guardian 24kW at 24,000 watts on propane and 21,000 watts on natural gas. That natural gas figure is the one most San Antonio buyers should look at first, and this guide explains why.
The ratings, engine and weight Generac publishes are on our Generac 24kW generator page, cited to Generac's product page and spec sheet.
The natural gas rating is the real one for many homes
Every Generac size above the 14kW is rated lower on natural gas than on propane, and the gap grows with the size. On the 24kW, Generac lists 24,000 watts on propane and 21,000 on natural gas, a difference of 3,000 watts. A homeowner who reads 24kW on the label and plans for 24,000 watts on a natural gas house has planned for power the unit will not deliver.
This is why we size from the fuel the house actually has. On a propane house, the 24kW is a 24,000 watt machine. On a natural gas house, it is a 21,000 watt machine, and the load list and the load management have to be built around that.
Larger homes and two air conditioning systems
Larger Texas homes often have two central air systems, one for each floor or each end of the house. Each compressor is a motor with its own starting surge, and if both start close together on a hot afternoon, the generator sees both surges on top of everything else that is running.
The 24kW gives more room for that than the 22kW does. Generac rates the 22kW at 19,500 watts on natural gas, and the 24kW at 21,000, so on natural gas the step up adds 1,500 watts. On propane, the step from 22,000 to 24,000 adds 2,000. Whether that headroom is enough depends on the two systems' data plates and on how the rest of the house is managed.
The middle size is covered in what can a Generac 22kW run, including how load management is set up on it.
What else a larger home asks of the generator
Larger homes tend to carry more of the loads that strain a standby generator. The nameplate on each appliance gives its running watts, and these are the ones that usually decide the size:
- Two central air systems, and how their compressors start.
- An electric range or double oven used during an outage.
- Electric water heaters, sometimes more than one.
- A pool pump, a spa heater, or a well pump.
- A second refrigerator or a freezer in the garage.
- A home office or medical equipment that has to stay on.
Few homes need all of these at once. The sizing work is deciding which ones must run, which can wait their turn, and which can stay off the generator entirely.
Load management still matters at 24kW
A bigger generator does not remove the need to manage loads in a big house. With two air conditioners and electric cooking on a natural gas 24kW, load management is often what keeps the total inside 21,000 watts. The usual setup keeps the air conditioning and the kitchen as priorities and lets the water heaters, the dryer and the pool equipment wait.
The switches that manage loads are in our guide to generator transfer switch types.
When the 26kW is the better step
If the list is still tight at 21,000 watts on natural gas, the next size is the 26kW. Generac rates it at 26,000 watts on propane and 22,500 on natural gas, so on natural gas it adds 1,500 watts over the 24kW. Generac also lists a 110 amp main line circuit breaker on the 26kW. Going to the larger unit is sometimes simpler than managing more loads; sometimes managing one more load is the less expensive answer. That is a decision for the sizing visit, with your plates and your panel in front of us.
The sizes side by side are on our Generac generators page, and you can book a free Generac sizing visit to settle it.
Mistakes that larger homes make
Larger homes tend to make the same sizing mistakes, only bigger. The first is reading the label and not the fuel: a 24kW on natural gas is a 21,000 watt machine by Generac's published ratings. The second is assuming two air conditioning systems can always start together, when the surge from both compressors at once is the heaviest moment the generator will see. The third is putting every circuit on the generator because the switch can carry the whole panel, and then having no order for what waits.
The fixes are the same as on a smaller home. Size from the fuel the house actually has. Stagger or manage the two compressors so they do not start at the same instant. And give load management a clear order, with the air conditioning and the kitchen protected and the large resistive loads waiting.
Long outages in a large home
A long outage is where a larger home feels the difference between sizes. After the first hours, the house settles into a pattern: the air conditioning cycles, the refrigerators cycle, and the family cooks and does laundry at different times. A 24kW sized from the right fuel figure, with a sensible order for what waits, carries that pattern without anyone thinking about it.
A long outage also runs the generator for many hours in a row. The owner's manual for the model sets the service intervals, and a unit that ran for days may be due for its oil and filter sooner than the calendar says. That is worth booking as soon as the utility returns.
- Size from the natural gas figure on a natural gas house.
- Plan how the two air conditioning systems start.
- Give load management a clear order.
- Book service after a long run, per the owner's manual.
A larger home also tends to have a larger service, sometimes more than one panel, and longer runs between the unit, the switch and the panels. Those details shape the transfer switch and the wiring as much as the generator size does, which is another reason the sizing visit looks at the panels and not only the appliances.
What the install involves
We set the unit where the setbacks allow, install and wire the transfer switch, pull the electrical permit, and start the unit up and test it under load, with a transfer test that confirms the managed loads behave as set. The gas line is a licensed plumber's work and is quoted separately. On a natural gas house with a larger generator, the plumber also checks that the meter can supply the generator along with the gas appliances already in the house.
The process is on our Generac generator installation page. We sell and install Generac home standby and commercial generators.
What a 24kW costs
The installed price is the unit, the switch, the wiring, the gas line, the placement and the permit. On a larger home, the distance from the unit to the panel, the panel's condition and the gas meter can move the price as much as the step from one size to the next.
Each part is explained in our Generac generator cost guide. We write your installed price after the sizing visit.