Can this boil-off rate be right?

Wow! I have a new 10 gallon Mega-pot from Northern Brewers. (Really nice pot, by the way). Before brewing my first batch with this pot, I decided to check what the boil-off rate is with it. I brought 5 measured gallons of water to a rolling boil (not an aggressive boil)and started my timer, set to 60 minutes - uncovered. When the timer indicated 60 minutes was up, I cut the heat, and cooled the water to about 90° with my immersion chiller. I then measured how much water was left. Surprise! Only 3 and 1/2 gallons left! Seriously?
Anyone else getting this high of a boil-off rate?

That's about what I get for boil off.

I boil off a gallon each 1/2 hour. So after an hour I would have only 3 gallons left. Your fine.

Seems alright, start with 7 gallons and get 5.5 out

I would say that 1.25-1.5 gallons per hour for a boil off is about right for most of us! Remember that boil off is a function of pot width and heat (and humidity- those in the desert boil off more than in Miami, for example), and not volume. So, if you start with three gallons, you'll boil off 1.5 gallons. If you start with 9 gallons you'll still boil off 1.5 gallons!

For a 5.5 gallon batch, 5.25 gallons to the fermenter, I start with 7 gallons in the winter, and 6.5 gallons in the summer (on humid days, I boil off less).

I lose right at 1/2 a gallon when I do a brew but I am only boiling 2.5 gallons instead of 5. Bigger pot would have more surface area for the water to release steam. I'm sure if I doubled my pot size I could expect the same to happen with my boil off.

I have a 10 gallon boil kettle and boil off just under 1 gallon per hour. But, it is what it is. You were smart to test it with water first so you can adjust your wort volume accordingly.

Cimerian said:

I lose right at 1/2 a gallon when I do a brew but I am only boiling 2.5 gallons instead of 5. Bigger pot would have more surface area for the water to release steam. I'm sure if I doubled my pot size I could expect the same to happen with my boil off.

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I would say it has more to do with the power of the burner/element, you put X amount of energy into the wort and that energy will convert X amout of wort to steam. Although the size of the pot comes into it because a smaller pot requires a smaller burner/element to be functional

I only boil off about a gallon per hour, but my stove is underpowered, and I keep the lid half-on to maintain the boil, so I lose less.

(Until next time - I just insulated the damn pot. Stupid aluminum and its high thermal conductivity.)

jcdouglas said:

That's about what I get for boil off.

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Hammy71 said:

I boil off a gallon each 1/2 hour. So after an hour I would have only 3 gallons left. Your fine.

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mattd2 said:

Seems alright, start with 7 gallons and get 5.5 out

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It sounded like a lot to me, but I guess I'm not alone. Glad to hear that.

Greyhound said:

You were smart to test it with water first so you can adjust your wort volume accordingly.

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It happens once in a while - the me being smart part.
Thanks for the replies.

Yooper said:

For a 5.5 gallon batch, 5.25 gallons to the fermenter, I start with 7 gallons in the winter, and 6.5 gallons in the summer (on humid days, I boil off less).

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That's just what Beersmith figured for my set-up.

My boil off is 1.2 gallons/hr. on a 11 gallon pot that's 13.5" in diameter. Your pot is 17" in diameter, so there is that much more surface area to evaperate, so one would expect it to have a higher boil-off rate, and 1.5/hr. sounds just about right!