Generator Calculator

What Size Propane Tank Do I Need for a Generator?

Generators use various fuel types, with propane being one of them. Propane gas comes packed in fillable tanks – portable or permanently installed models you keep filling in your property. However, during an emergency or a disaster, generator fuel can be a challenge to come by. What’s more, a small propane tank has the inconvenience of making you get out of the house to change it when fully used. Those are some of the reasons you might want to know the ideal generator propane tank to power you through the power outage.

A generator propane tank sizing chart is what you need to ensure your backup power supply stays reliable during the power outage. But, there will be the need to stop the generator at least once in 24 hours of operation to prevent wear due to extended operations.

However, you still need to run as long as you can to keep your food fresh, warm the house, keep the lights on and connect to the rest of the world. That’s why it’s crucial you estimate the perfect propane tank size your generator needs to keep you powered all through the emergency.

And this post gives you that and some valuable data necessary for estimating how much propane you will need. I should mention, though, the amount of propane your generator consumes depends on:

  • Load hooked up to the generator (watts you’re drawing from it)
  • Your generator model and its efficiency (tough to calculate)
  • How many hours you’ll run the generator per day

How to Size a Generator Tank (Simple Estimation)

Considering you know your generator size, what you need to run during the outage, and for how long, here is how you can estimate the size of propane tank you need.

Step 1: Finding out the amount of propane your generator needs in an hour

Most manufacturers will provide information on the fuel efficiency of a generator in the documentation.

You should get the information on how many propane gallons your generator uses in an hour to produce the wattage it generates.

If the documentation isn’t available, you have the option to contact your generator manufacturer and enquire about its fuel consumption in gallons per hour.

Step 2: Get the amount of electricity (wattage) you plan to withdraw and for how long

With backup generators mainly used with home essentials that you have to run during an emergency, it would be best to establish your essentials list.

Take a pen and a paper and go around checking the wattage of your essentials. This information is available at the appliance back or bottom detail sticker.

If the information isn’t available, you can find it in the appliance manual. It might not be given in watts at times, but you can get it by multiplying the amperage with voltage.

Also, estimate how long the utility power will take to get back on (in hours) – you can use the previous blackout lengths as your estimation base.

Step 3: Calculate the amount of propane you’ll need

By taking the FC (fuel consumption) and multiplying it with how long the generator will be running, you will get the amount of propane the generator needs to run at full power until the power is restored.

Amount of propane your generator needs = Generator’s Fuel Consumption (FC) x Hours it will operate during the blackout.

What you get here is the fuel amount in gallons, which you’ll have to convert to pounds to know what tank size suits you best.

In an example:

Suppose you have an 8kw (8000 watts) generator, and you need it to power a refrigerator, lights, heater, mini-AC, and TV for 36 hours. Assuming these appliances and devices will consume 80% of 8000 watts, you can assume it’s operating at full capacity. In the generator manual, you found that the generator consumes 2-gallons of propane in an hour. That means the generator will burn:

3-gal/hour x 36 hours = 108 gallons of propane

And with 4.24 gallons of propane equaling one pound of propane:

You’d need:

108/4.24 = 25.5 pounds of propane

How to Size a Generator Propane Tank Using Load Base

But these figures are an estimate you get when you assume the generator operates at total capacity during the entire blackout.

If you want a more accurate estimate, you have to take the load you draw from the generator to know how much propane it burns during an emergency.

You will also need to add the contingency (the extra gallons burnt because of the extra load you might connect for few hours.)

Total propane = propane used in an hour x hours the wattage is drawn + contingency

How Much Propane Can Your Generator Consume Per Hour?

Working out the amount of propane your generator will consume to power your appliances per hour, it’s time to get into the numbers. But don’t worry, the calculations are simple.

But before then, there few assumptions that we’ve to make about typical generator efficiency and use them in our calculations.

  1. 1HP of electric power will produce around 746 watts of power.
  2. Mechanically, 1HP of mechanical energy requires 10,000 BTU fuel per hour.
  3. Propane fuel value is estimated at 92,000 BTU per gallon
  4. Lastly, propane gas is estimated to weigh 4.24 pounds per gallon

Step 1: Calculate the electrical horsepower needed to run your appliances

Horsepower = Base load in watts / 746 watts

Assuming the total wattage of your essential appliances that you will run during the power outage adds up to 4000 watts, you need:

4000 watts / 746 watts = 5.36 Horsepower (Electric)

Step 2: Relate the Electric Horsepower to BTU

1HP = 10,000 BTU

In the example, our 4000-watt load requires:

5.36 x 10,000 = 53,600 BTU of fuel per hour

Step 3: Calculate the amount of propane needed

1-Gallon of propane = 92,000 BTU

From our example, your generator can consume:

53,600 / 92,000 = 0.59 Gallons of propane to run 4000-watt load in an hour.

How Much Propane Will Your Generator Consume During the Blackout?

Here, you need to put the three steps together to form a formula:

Propane Consumed per Hour (Gallons) = (watts/4000) * 0.59

And with:

1 Gallon of propane = 4.24 pounds of propane, therefore:
20 pound propane tank = 20/4.24 = 4.717 Gallons of propane

From our example:

4.717/0.59 = 8 hours

That means, with a 20-pound propane tank, you can run your essentials for around eight hours. However, if you needed enough fuel to run the same appliances for the same hours but three days, you’d need approximately 60 pounds of propane, which means you’d need to order a 100-pound tank.

However, these are estimates, which do not take into account generator efficiency variations. But, they can give you a base to start from when drawing the ideal generator propane tank sizing chart for your needs. Remember not to underestimate – it’s better to have spare fuel than running out during an emergency.

What if you have some appliances running momentarily?

In reality, the amount of power you’ll be drawing from your generator won’t be constant. But, yes, you have the baseload that stays constant for a given period like the freezer, TV, refrigerator, and the likes.

But there some high-watt appliances you only switch on momentarily, such as the washing machine or microwave.

For such a case, it’d be best to include the peak load to help you get a more accurate amount of propane your generator will need to run essentials, including the peak hours.

Total Propane Generator Consumes = (Base load/4000 x 0.59 * hours to be run) + (Extra wattages in peak hours/4000 x 0.59 x hours to be run)

An Example:

Suppose I’m using a portable Champion Power Equipment 200988 Inverter Generator delivering 4500 starting and 3500 running watts.

I want it to run my refrigerator (500 watts), deep freezer (500 watts), Laptop (50 watts), space heater (100 watts), and LED TV (100 watts) for 14 hours for 36 hours.

I also want to use my instant hot shower (150 watts) for 0.5 hours and run a 1HP Sump pump (400 watts) for 3 hours in the 36 hours. I will also need to use the lights (60 watts) for 5 hours per day.

That means:

Base load = 500 + 500 + 100 + 100 + 50 = 1250 watts for 14 hours per day for three days

Extra wattage in peak hours = hot shower (150 watts for half an hour per day for three days) + Sump pump (400 watts for 3-hours per day for three days) + lights (60 watts for 5 hours per day for three days)

So:

Base fuel consumption = (1250/4000) x 0.59 x 14 x 3 = 7.7 Gallons of propane
Extra fuel consumption = ((150/4000) x 0.59 x 0.5 x 3) + ((400/4000) x 0.59 x 3 x 3) + ((60/4000) x 0.59 x 5 x 3) = 0.033 + 0.531 + 0.133 = 0.697 Gallons of propane

Total fuel consumption = 7.7 + 0.697 = 8.4 gallons of propane

But:

1-Gallon of propane = 4.24 pounds, so, 8.4 gallons = 8.4 x 4.24 = 35.6 pounds of propane.

Generator Propane Tank Sizing Chart – List of Available Tank Sizes

Most dual-fuel that has the option of running on propane or propane-fueled generator is designed to use a 20-pound propane cylinder designed to hold approximately 4.72 gallons of the gas when full.

And as you can see from the calculations, a propane cylinder isn’t enough to run most house appliances for more than a day; at times, it might not even make it in a day – unless you stay conservative in the amount of power you use.

If you think the blackout will take more than a day and staying without power isn’t an option, you can get multiple 20-pound cylinders or install an in-site propane tank.

But you’ve to bear in mind connecting a large on-site tank isn’t that simple like using a portable cylinder. What’s more, you will still need to stop your generator for maintenance. Although it can help reduce wear and tear for a prolonged life – it’d be best to avoid running it for 24-hours a day.

Common Generator Propane Tank Sizes

Common Residential Propane Tanks
Tank sizeCommon UsesSize and CapacityPlacement
20 lbs.Generator, home barbecues, patio heaters, mosquito catchers, etc1.5 feet tall, 1-foot diameter and 5-gallon propane when full.Away from fire and anything that can cause fire
33 lbs.Generator, forklifts, and most of the auto-gas-fueled vehiclesApprox. 2 feet tall, 1-foot diameter, and 8 gallons when full.Away from fire and anything that can cause fire
100 lbs.Residential fireplaces, dryers, cooking, temporary commercial heat for job site4 feet tall, 1.5 feet diameter and 25 gallons when full3 feet from your home doors and windows and 5 feet from any source of ignition
420 lbs.Hot water systems, home heating, generator, pool heater, fireplaces, and more4.5 feet tall, 2.5 diameters, and 120 gallons when 80% full5-feet away from your house and 10 feet away from any source of ignition.
500 lbs.Whole-home systems, generators, home heating systems, pool heater, and more3.5 feet tall, 10 feet long, and 400 gallons when 80% fullTen feet away from your house, any source of ignition, and property line.
1000 lbs.Whole-home systems, generators, home heating systems, pool heater, and more3.5 feet tall, 16 feet long, and 800 gallons when 80% fullTen feet away from your house, any source of ignition, and property line.
30000 lbs.Commercial facilities, large communities using metered services, plant storages, and huge consumption applications10 feet tall, 70 feet long, and 24,000 gallons in capacity at 80% fullInstallation regulated by local and state regulations

Propane Consumption Chart

Propane Consumption chart based Base Load

(Assuming the load stays constant during the emergency)

Base LoadFuel Required in lbs. per hour
18501.16
40002.50
50003.13
75004.69
80005.00
10,0006.25
12,0007.50

Final Thoughts!

Even though you might have never experienced a blackout or power outage extending more than few hours, it’d be best to be prepared by knowing how to estimate your generator propane consumption. The information in this post takes you through the few calculations involved and gives you some figures you might want to consider next time you’re stocking propane gas.

About the author

Sharif Gen

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