rolling boil

I have noticed an increase in evaporation during the cold spell we had in AZ.
I lost over three gallons some in the grains but most in the 60 minute boil. It is something I've never put much thought into. A friend of mine states he boils as low as possible "212 is 212".
I'm sure breweries use as least amount of energy as possible.
My kettle is 14"I.D. X 12" tall, lots of surface area per gallon. I could cover it, or just lower the flame to hold 212 degrees. I usually vigorously boil my Indian Brown Ale for some carmelization and lightly (still rolling)boil my lagers and Pales.
The last brew was started with 8 gallons of water and I ended up with 4 gallons in the fermentor. Grains and bottom of the kettle account for less than a gallon I would guess. Slightly high S.G. Added .5 Gal. To hit Recommended (beersmith) gravity.
This seems like too much loss, any ideas?




Fermeting: Old Ale, Special B Bitter
Secondary: Pale Vienna, German Alt.
On Tap:APA, Scotch Ale, Porter

Once your wort reaches ~212 thats as hot as it will get at normal atmospheric pressure, after that it will turn to vapor. If you apply artificial pressure using a pressure cooker, you can increase the temperature the liquid will get before it evaporates. By throwing more heat to your wort all you do is just increase the evaporation rate. Once my wort starts to boil, I lower the flame to maintain a boil to minimize my evap rate.

212F is not 212F, reading material here:

http://en.wikipedia.org/wiki/Latent_heat
http://en.wikipedia.org/wiki/British_thermal_unit
(More heat (btus) = more boil off)

You don't want to use a lid either, you need a rolling boil to blow off nasty compounds like the precursor to DMS. When boiling you really want two things:

1) The lowest heat setting that maintains a rolling boil. (Typically, unless trying to rapidly reduce volume)
2) Predictability, so that you can try to always boil from 7.5g down to 6.0g, or whatever your preferred volumes are.

Cheers!

Once it is boiling and you have had the hot break drop then you can go down to a nice even boil. A boil is not always 212 degrees either. I am higher up and my boil never reaches 212. Thankfully though the DMS will bil off at a lower temp and the hops will still get utilized.

I brewed last night and lost 2 gallons in the boil just because it is cold here. No problems though because I knew it was going to happen and planned for it. Finding what works for you and your set up is half the fun and well aggravation.

Thank you all for the input.
I will adjust my flame after hot break to the lowest boil and see how it turns out.
Home brewing is a learning experience every time!

I am at 740 feet elevation, and after the boil has started, I simply reduce the flame to maintain a boil. I don't own stock in a propane company. My boiloff is what most people seem to report- 1-1.5 gal. in 60 minutes. The beer is fine.