How to calculate electrical load for generator purchase

[exnisstech]

Can someone help with this? I want to replace my older gas powered generator with a dual fuel since we have a 500 gallon propane tank supplying the house. I need to know how I would calculate how much power I would need to supply. I have no idea at all how to calculate this so pretend your talking to a child and be patient I already have a manual transfer switch wired to my breaker box with a box on the back of the garage to connect the generator to the house. I'm looking to be able to power 2 tanks with sumps, 2 freezers, a fridge and a couple of lights. I have a woodburner so if I loose power in the winter I don't need the furnace as the wood burner requires no power and will heat the entire house. Maybe there is a cheap power meter I can use? I'm looking to spend less than $1k on the generator the less the better but I don't want to be underpowered and not be able to run what is needed so I'm open to suggestion on a unit as well. Thanks in advance.

 

[BraindeadBiologist]

Hey so I found a link on Google that explains everything in detail about your power drain, size of the home, etc but basically:
Amps = watts / volts
Volts x amps = watts
These are two simplified formulas that can help you calculate not only the capacity of your entire electrical service, but also those of individual circuits. For example, if you have a 100-amp service with a 240 volts circuit, then your total capacity is 24,000 watts.

Since the recommendation is not to exceed 80% of the total capacity, that puts you at 19,200 watts. This means that all your appliances, devices, lights, etc should not exceed 19,200 watts at any given time in order to avoid an overload.

All light bulbs and appliances come with wattage ratings, so it shouldn’t be hard to calculate the total wattage amount.
OR
Start by adding the wattage of all lighting branch circuits.
Add in the wattage rating of all plug-in outlets.
Add in the wattage of all permanent appliances, such as washer/dryer, electric range, or water heaters.
Subtract 10,000 & multiply this number by .40
Add 10,000.
Add the wattage of your AC or heating appliances (furnace + space heaters), whichever is greater – Don’t add both!
Divide by 240.
OR Read this link in its entirety. https://pennaelectric.com/electrical-load-calculation/
Electrical is not something to take lightly. At the end of the day, even though I did all the math, I would still seek expert advice.

 

[WVNed]

Add up the watt ratings of everything you want to run and add 20%

I ran my 240 and 75 plus a chest freezer and some misc stuff with a 3500 watt.

 

[exnisstech]

Add up the watt ratings of everything you want to run and add 20%

Thanks. So just use the max stated on the device? Say bulb is 75 watts and a pump is 525 so I have 600 watts total less the 20%? Easy enough. I assume the 20% is a cushion?

 

[WVNed]

Thanks. So just use the max stated on the device? Say bulb is 75 watts and a pump is 525 so I have 600 watts total less the 20%? Easy enough. I assume the 20% is a cushion?

You asked a complicated question. I gave a simple answer. The complex part comes from when the compressors start in the fridge/ freezers. They momentarily use a lot more power to start than they use just running. The 20% is to get you through that.
Light bulbs, aquarium heaters and small pumps are just add up the watts.

We have a 32k Generac now. We can run everything.

 

[WVNed]

When buying a generator make sure you are comparing them correctly. Most list a running output and a momentary output that is much higher.

The longer your power is out the more you will want to plug stuff in to make yourself comfortable like the microwave or coffeepot

Go to the generac website. I believe there is a backup generator sizing estimator there.

 

[KStatefan]

As @WVNed said look at running watts

 

[exnisstech]

Thanks folks. I'll get the wattage off of everything and add the microwave and coffee pot I think this is one of those things like horse power and money in the bank, too much is just enough.

 

[RedoubtReef]

Is your generator the only thing running on propane?

 

[Big Smelly fish]

You be surprised at how much a portable generator will run. For years I have used a 7500 hundred watt generator, my son is an electrician and wired into electric panel with a switch to kill power from the poll.
I could run everything but two water heaters. And 3 ton AC. But would run the 1 ton that cools the bedrooms. Here in south Louisiana we have lost power fir 7 to 20 days at a time. It’s expensive to run them but worth it.
now I have a whole house 22k that runs on propane.

 

[exnisstech]

@RedoubtReef

Furnace and water heater are on propane but wood is my main source of home heat so in really just the water heater. I've been wanting to do this since I have a 500 gallon propane tank I would like to plumb it to a gen so I don't have to store and lug gas from the shop.