Hot Liquor Tank Size

I see these 3 pot fancy horizontal brewing systems, with what seems to me is an oversize hot liquor tank. I feel like it doesn't really need to be that large? You be able to change temperatures faster with a smaller one. Thoughts? Comments?

Needs to be sized to accomodate the largest of:
Mash Water Volume
Sparge Water Volume.

I would not want less than 10G for 5G batches, 15G for 10G batches.

All my 5gl batches use ~10gl, why not have the biggest BK to upgrade in the future, its inevitable....

If you can heat the HLT to strike temp with its own heating element then you can downsize the HLT. To come up short your screwed. Adjust the volume needed in a large HLT to the batch your brewing for a faster temp rise.

But couldn't I effectively use my 10 gallon boil kettle to heat my strike water, use it, heat up my sparge water, put it in a seperate sparge cooler, then lauter/sparge directly into the boil kettle?

All while using my 5 gallon kettle with a coil submersed in it as my HLT?

That is a lot of work to save the the small incremental cost and space. I understand what you are proposing, but it is a lot easier to have a dedicated HLT.

The way i use mine gives me flexibility that i think you may want.

regardless of batch size i heat up 13 gallons (in a 15 gallon HLT). Then after I add my mash water, i top the HLT up to 13 gallons again (adding 110 degree water conveniently lowers the HLT temperature approximately to the Mash Temperature for HERMS recirculation). So now i have 13 gallons of hot water. I add my sparge water which leaves between 6-9 gallons of hot water left in the HLT. I turn the HLT off, and it keeps the water hot. the remaining water i use to clean my system.

Ok that makes sense to me, but how do you accurately measure how much strike water, and how much sparge water you're removing?

I guess what I'm saying is, if I have 15 gallons of HLT water. And I need 4.5 gallons of strike water, how do I accurately get that off? I understand I'd need to pump it over. But does this require a sight glass (which I'm not opposed to doing)? How else would you do it?

You start with 13 gallons, you need 4.5, so you pump till you are left with 8.5 gallons...

Yes, you would need a sight glass. Well worth it in my opinion

It really depends on the process you use. Personally I heat up just my Mash Water, then add the total sparge and heat that while mashing so I can get away with a smaller HLT. When I have a sight glass, I might do things differently.

The HLT only needs to be as large as the largest single infusion you'll need. It varies by batch of course.

Yes, you can use your boil kettle as the main heating vessel and then move the water to a temporary holding vessel. If you want to fly sparge, it needs to hold heat so a cooler is great. If you batch sparge, it can be a bucket because you'll be dumping it to the next step in 5 minutes.

I am using a corny keg for an HLT. I heat my strike water in my BK. Use the HLT for heat exchange and I batch sparge with the water from the HLT.

I use 14 gallone easily between infusions, sparge, and cleaning.