How much water storage do I really need?

[mwk1000]

I rely on maxing out my storage to 185 +/- each night and bringing it all the way down to 140 (sometimes lower) before I start the next fire. Overall, and some may disagree, I don’t think you can get the same responsiveness and performance in this broad a range with non-pressurized tanks.

That is 45 degrees * weight of water in your tank. Each situation is different, I have an open tank I use from 170-110 for 60 Degrees * my water mass. It heats just fine. I have the EDPM with a plate HX external.

I used a spreadsheet when figuring out how big with just the information the guys here are talking about.
1) Usable heat range for YOUR home, radiant ? Forced Air, etc.
2) Burn time needed to charge the tank to "full" This is where larger is not allays better. And a reasonable estimate of your boilers output is needed.
3) # of hours you want to run before burning again. ( This requires knowing your heat load ) I was aiming for one burn per day on the coldest day.
I balanced these things and came up with how many BTU's I would need and then backed that into gallons of water and came out with 1500.