Mash water req'd for batch sparge

I've finally graduated to full boil/all grain. Done 4 so far. Let's assume single step infusion and "batch sparge" with 2 equal runnings. I need BV=7gals for a 1 hour boil. Do I need to do a "mashout" to raise temp to 168? If I mash thin, then there's not enough water available to add at mashout to raise the temp and still get 2 equal runnings. If I don't need to mashout, then can I just mash thin enough to get 1/2 my BV and just drain the tun for 1st runnings? How much wort can one expect to produce from a given grain bill?  At what point is your grain bill so big that you need boil for 2 days; make 2 batches; get a bigger system; leave extract behind because you quit lautering when you'd collected all the wort you needed; tweak grain bill 'til you get efficient mash and add DME to boil?

FUZZYV said:

I've finally graduated to full boil/all grain. Done 4 so far. Let's assume single step infusion and "batch sparge" with 2 equal runnings. I need BV=7gals for a 1 hour boil. Do I need to do a "mashout" to raise temp to 168? If I mash thin, then there's not enough water available to add at mashout to raise the temp and still get 2 equal runnings. If I don't need to mashout, then can I just mash thin enough to get 1/2 my BV and just drain the tun for 1st runnings? How much wort can one expect to produce from a given grain bill?  At what point is your grain bill so big that you need boil for 2 days; make 2 batches; get a bigger system; leave extract behind because you quit lautering when you'd collected all the wort you needed; tweak grain bill 'til you get efficient mash and add DME to boil?

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No, you don't necessarily have to do a mashout.  I seldom do.  I try to mash with enough water so that I get half my boil volume from the mnash without further additions.  That usually puts me in the 1.6 qt./lb. area. 

You can still do the mash out. use a portion of the sparge water to do it instead of  adding extra water on top of that. just take a bit of the sparge and throw it on the stove in the kitchen. Bring up to the temp you want and add it to your mash tun that way your not adding more water and your not messing up your amounts . If this isn't correct maybe I am misreading your question. as I read your post I not sure if your saying your wanting to two batches via one grain bill? and you should never boil for 2 days ever .. If you are talking about doing two batches via one bill then your wanting to do a parti gyle .  which means you will need another keggle 3 in all .. and i think the biggest you can add to a 10gal. igloo is around 25lbs of grain and at 1.5qt water/1lbs grain, your really going to be pushing your limits.


I could be way off on my answer as i think i have confused myself on your question lol

Thanks for the input so far.
Allow me to try and clarify. The 2-day boil time was tongue in cheek to demonstarate that there is no free lunch.
I have a 10 gal MLT. I need BV=7 gals. 7/2=3.5 gals= 2nd runnings or sparge 2. Mash + mashout= 5 gals including grist and tun losses. eg: 20 lbs X 1 qt/lb = 5 gals. This would be drain and sparge once but, this is way thick, so at 1.25/1 its now 6.25 gals and there's only 2.25 gals left to play with. Clearly there ain't enough H2O here to raise the temp to 168F nor is there enough for 2 equal runnings. Do you just stop lautering at 7 gals and waste the extract created or do you sparge with 4.75 gals for a total EV= 9.5 gals and boil as long as it takes to get to 6 gal post boil? That'll take 2 kettles and probably 2 hours or yadda yadda.
Isn't there some rule of thumb? How big of a grain bill can you efficiently mash/lauter and end up with 7 gals of wort for the kettle without wasting any more in the MLT? I'm aware that you lauter until SG gets to 1.010 or so and/or your pH starts going up. I've read that with the "batch sparge" process these are not of major concern. As a check on sparge H2O needed, I set an upper limit of 2 qt/lb and it becomes clear that on small grainbills that you need to add H2O to the kettle to get BV because you come up short on the lauter without running into the danger zones.
Thanks