large volume loss? (and other general questions)

Hi all,
First I want to say how blown away I am by this site. Everyone has been so helpful, and willing to take the time to pass along their knowledge to a rookie brewer. Makes me think if everyone brewed this would be a much better planet...

So, this will be a bit of a long post so please beer with me. First, here is the recipe that I developed. I loosely based it on a few double IPA recipes I have looked at. (Also this is my 4th beer ever, so props to me for working up my own recipe )

5.00 gal Poland Spring (R)Water (for mash - did sparge w/ tap)
8 lbs 8.0 oz Pale Malt (2 Row) UK (3.0 SRM)
2 lbs Pilsner (2 Row) Ger (2.0 SRM)
1 lbs Cara-Pils/Dextrine (2.0 SRM)
1 lbs Vienna Malt (3.5 SRM)
3 lbs Amber Dry Extract (12.5 SRM) (amended down to 2 lbs, see below)
1.00 oz Simcoe [13.00 %] - Boil 90.0 min
1.00 oz Simcoe [13.00 %] - Boil 60.0 min
1.00 oz Citra [12.00 %] - Boil 30.0 min
1.00 oz Simcoe [13.00 %] - Boil 20.0 min
0.50 ozSimcoe [13.00 %] - Boil 15.0 min
1.00 oz Citra [12.00 %] - Boil 5.0 min
2 packets Safale American (#US-05) Hydrated in 230ml sterile H2O
1.00 ozCitra [12.00 %] - Dry Hop 7.0 Days
1.00 ozSimcoe [13.00 %] - Dry Hop 7.0 Days

Mash: Single Infusion, Medium Body, No Mash Out
Mash In: Add 15.63 qt of water at 163.7 F 152.0 F 60 min
Fly sparge with 4.63 gal water at 168.0 F (was closer to 172F)

I did rinse (volurof?) the grains with the wort 3 times before I started the sparge. When finished I took an SG and got 1.060, which with the brewhouse efficiency calculator on line gave me an efficiency of just over 83%! :rockin:
At this point I realized, (while looking at my beersmith recipe, which had estimated my efficiency at around 75%) that if I added all 3 lbs of the DME I would go way over my target OG of 1.090. So I amended the recipe and only added 2lbs of the DME and wouldn't you know it, my OG was exactly 1.090.

My problem: I did a 90min boil at this point, starting with 6.75 gal. It did take a while (about an hour) to get up to a boil, as I am definitely maxing out my stove top capacity (gas, pot on 2 burners, one a high efficiency burner). At the end of the boil and cool, I was only left with about 4.6gal.

So the question is, how did I end up with so much more boil off loss then expected? Was it because it took so long to get up to temp? I was thinking if this was the case (which I am guessing it is) couldn't I just cover the pot until it gets up to temp? I read somewhere that if I do this I can expect massive boil over. Does anyone know if this is true? If it is could I cover the pot to prevent loss if I remove the cover at about 205F? Or any other suggestions to prevent this excessive loss? (other then buy a super high efficiency burner that would require I brew outside, where it was < 20F yesterday)

Lastly, any general comments on my recipe are more then welcome!
Any and all comments appreciated!

Well, you have a problem. However I am confused a tad, did you boil for 90 minutes after the boil started? In any case you know the answer, the length of time on the burners is why you lost the volume.

However, you do not want to leave a lid on your pot due the formation of DMS (Dimethylsulfide) compounds in the vapor that will collect on the lid and fall back into the wort. This is one of the reasons for a vigorous boil, to drive off DMS. Also, yes the brew will boil faster with a lid on and typically you cannot avoid a boilover because it is hard to predict (boil temperatures vary with barometric pressure), kinda depends on your pot size and batch size, etc. Also, I usually see boil at my place around 205F due to the altitude, so there are some variables

One thing you may want to look into is a heat stick, these are electrically heated elements that will heat the brew faster. Here is one thread: https://www.homebrewtalk.com/f51/heatstick-awesome-142803/
There are many more, just search heat stick above or on google.

Yes, I did boil for 90min once the boil started, so it was on heat for about 150min total. Plus an extra 15 minutes on top of that because I had to pour all 6.9 gal into 2 smaller pots, and replace a gasket on the thermometer because it started leaking like crazy after about 20min on the stove! (First time I used this brew pot) I will definitely look into a heatstick. Thanks for the tip!