What Size Propane Tank You Need For A Whole House Generator?

While many of the products we review here are readily available to purchase and operate without a license, we always recommend hiring a qualified electrician to install and demonstrate their use.

In some cases, improper use and installation may result in a breach of insurance. Even worse, you could be putting yourself or your family at risk as an incorrectly installed electrical device could start a fire. So, don’t risk it - seek the services of a fully licensed electrician instead.

If you have a natural gas supply underneath or near your property, fantastic!

All you need to do is pay for your whole house generator to be plumbed in, and voilà… you’re protected from blackouts! 

Unfortunately, though, we’re not all lucky enough to have this sort of infrastructure around, and in the absence of a natural gas line, the only alternative is to install a sizable propane tank somewhere on the property.

What Size Propane Tank You Need For A Whole House Generator?

The question then becomes… How big does this fuel tank need to be?

With so many variables involved, it’s a deceptively complex question, but I’m going to simplify it today by taking you through all the key considerations when deciding on fuel tank size for your whole house generator.

Propane Tank Size: Key Considerations

Generator Specifications & Outage Duration

Your propane tank needs to be able to power your whole house standby generator, so before selecting one, take a good look at your generator specifications.

As an absolute minimum, your propane installation should be able to provide one full tank to your generator.

That way, you’ll be backed up for the entire length of its advertised runtime — No guessing!

That said, I’d highly recommend going well, well beyond a single tank with your on-site propane installation, as you don’t know how long a power outage is going to drag on.

Having a backup generator that runs for 2 days straight on a single tank is no good if a blackout lasts 3 days or more.

Now, if you’re fairly certain you’re only going to be dealing with short-term outages, sticking to the minimum is absolutely fine, but if you’re expecting numerous short-lived outages in close succession, it’s best to bring in as much headroom as you can realistically afford and your property can accommodate.

Manufacturer Recommendations

No one knows your generator like the manufacturer, so it’s best to inquire with them regarding the size of propane tanks, but bear in mind that even they don’t understand your individual needs and how you plan on using the power provided by your generator.

Don’t take everything they say as gospel, but do use it as a baseline to make your own assertions.

So, what are manufacturers likely to tell you?

Well, for 1 to 2 days of power, you’ll most likely be quoted something along the lines of 120 gallons, but that’s only if you absolutely have to choose something smaller due to spatial or financial constraints (more on those in a moment).

Personally, I wouldn’t recommend going for a 120-gallon propane tank, as it’s simply not enough to make the most out of your whole house generator.

These stationary backup power supplies cost an arm and a leg, so you want to get your money’s worth out of yours, and 1–2 days power during emergencies that could last much longer isn’t worth your initial investment.

Generator manufacturers themselves will explain that a 250-gallon propane tank is going to be a much better option, but even that’s going to limit your generator’s potential.

If you want comprehensive long-term coverage from your generator, a 500-gallon propane tank is a must!

Depending on the specifics of your installation and how you use it, you can expect a tank of this size to last between 8–10 days.

120 Vs. 500 Gallon Propane Tank

Here’s what the folks over at Generac say about the difference between 120 and 500-gallon propane tanks for whole house generators:

  • 22 kw generator — 120 gallon = 48 hours // 500 gallon = 197 hours
  • 20 kw generator — 120 gallon = 50 hours // 500 gallon = 210 hours
  • 16 kw generator — 120 gallon 59 hours // 500 gallon = 246 hours
  • 7.5 kw generator — 120 gallon = 138 hours // 500 gallon = 574 hours

Side Note — These averages are based on Generac’s own line of whole house standby generators, so they’re to be taken with a grain of salt.

Property & Family Size

The larger your property and the more people living within it, the larger the load on your whole house generator, and the faster you’re going to burn through your fuel.

500-gallon propane tanks are considered the average across the nation, but if you have a larger than average property/family, 1000 gallons may be the only logical option for you.

Propane companies consider 4500 square feet to be the threshold that splits homes into 500 or 1000-gallon categories.

If your house is smaller than 4500 square feet, 500 should be as big as you go, while those with houses larger than 4500 square feet will likely benefit from a 1000-gallon installation.

Space

It’s not just the space within your home you should consider, but the space on your property for the installation of your propane tank.

The larger the tank, the larger the space you’ll need to give up to accommodate it.

So, if space is running a premium, or perhaps you just enjoy the space you do have, a smaller propane tank is likely the most suitable option.

Cost

Needless to say, the upfront costs of purchasing and installing a small propane tank are lower than those for a larger propane tank, so if purchasing the generator itself has left you a little strapped for cash, you might need to shoot for a more modest fuel tank.

However, in the long run, it’s possible that a larger installation would prove the more affordable option, as you can often secure bulk deals when buying larger volumes of fuel.

Final Thoughts

Think carefully about all the points discussed in this post to estimate a suitable propane tank size for your property.

While 120 gallons is considered the absolute minimum, I would advise treating 250 as the baseline option, otherwise, you’ll be caught out by longer outages.

A 500-gallon tank is an even better choice, as evidenced by the fact that it’s the most popular fuel tank installation in the US.

It cuts a good balance between cost and performance, but even this tank size won’t be enough for larger households with mammoth backup generators.

For comprehensive blackout protection, larger properties should have a 1000-gallon propane tank installation, no two ways about it!