# Stand alone calculators for electric brewing

#### LarryBrewer

##### Active Member
From a user who contacted us by email:

How about a calculator for electric brewers to determine necessary watts needed to bring 3gal,5gal,10gal etc. to a boil and how long it will take to reach a boil? Also formulas such as watts\\volts=amps etc. would be useful.

Anybody have a source for equations on this?

http://homebrew.stackexchange.com/quest ... ou/592#592

down vote

The formula to determine wattage is as follows:

Gallons * Temp Rise (F)
------------------------------------ * 1000 = Watts Required
372 * heat up time (hours)

So, for a homebrew example of 7 gallons of wort at the beginning of your boil, and desiring to reach boil in 15 minutes, and assuming your wort temperature before boil is 150 degrees F after sparge runnoff:

7 * (212 - 150)
---------------------- * 1000 = X Watts
372 * .25 hours

Or 4666 watts.... or a 4500W element.

Besides the formula in perfect conditions, its also relative to the conditions, different pots, different insulation, different weather, pressure temps, elevation ?? Whether you're using pid pulse or on full power also??, with the lid on or off too

Good points.

http://e-brewing.tumblr.com/

read down at Fun With Heat Elements and Math

he has done some work on the subject with electric only

The basic forums looks like this:
target temp - start temp = temp rise needed
temp rise needed / temp rise per hour provided by element * 60 minutes = minutes needed to reach target temp from start temp with element

220v:
Striking:
(18766 BTU/h) / 83.4 = 225F / hour
50F rise needed : 50F / 225F rise per hour * 60 min = 13 minutes to strike

Boiling:
(18766 BTU/h) / 62.55 = 300F / hour
57F rise needed : 57F / 300F * 60 = 11.4 minutes to boil

110v:
Striking:
(4691.5 BTU/h) / 83.4 = 56.25F / hour
50F / 56.25F * 60min = 53 mins to strike

Boil:
(4691.5 BTU/h) / 62.55 = 75F / hour
57F / 75F * 60min = 45.6 mins to boil

2x 110v:
Striking:
(2 * 4691.5 BTU/h) / 83.4 = 112.5F / hour
50F / 112.5F * 60min = 26.5 mins to strike

Boil:
(2 * 4691.5 BTU/h) / 62.55 = 150F / hour
57F / 150F * 60min = 22.8 mins to boil

LarryBrewer said:
From a user who contacted us by email:

How about a calculator for electric brewers to determine necessary watts needed to bring 3gal,5gal,10gal etc. to a boil and how long it will take to reach a boil? Also formulas such as watts\\volts=amps etc. would be useful.

Anybody have a source for equations on this?

See this: http://www.phpdoc.info/brew/boilcalc.html

and also cross-referenced to my request today: http://www.brewersfriend.com/forum/viewtopic.php?f=7&t=1085

One issue in the source code of that equation is that when both "Start Temp" and "End Temp" are in units of Farhenheit and "End Temp" exceeds 99F, it always throws an error message of "Start temp cannot be greater than End Temp" even when "Start Temp" is less than "End Temp". It only does it when "End Temp" is in triple digits >=100F and my guess is that it still error checking based on a maximum boiling point of 100C and doesn't recognize hot, but not boiling water temps of 100-212F.

Quality Home Brew said:
Besides the formula in perfect conditions, its also relative to the conditions, different pots, different insulation, different weather, pressure temps, elevation ?? Whether you're using pid pulse or on full power also??, with the lid on or off too

All of that mattters, yes, but the main point is to give electric brewers a ballpark idea of how to size their element or what to expect when mashing, boiling, etc... Real world conditions aside, they'll only affect the difference between boiling with an aluminum pot and a PID heater and boiling with a keggle and a PWM heater by about 5-10%, which equates to only a handful of minutes either way.

The more important aspects are insulation and elevation, but even those won't affect the heating times by more than an additional 10-15%. Still well within a ballpark limit of 20% to either side for heating with electric.

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