So I have poked around on the forum here now getting ready to have a more comfortable house by moving to a gasification boiler vs a wood burning insert. My dillema is I have somewhat limited space in my basement and my access is rather tight, so I have been weighting my options as far as what I am can get/need for thermal storage. The specs on the house are 1922 bungalow, 1750sq ft, with blow insulation walls, and ALOT of windows 39 to be exact The house air change is rather tight, based on a recent energy audit, blower door test, and the FLIR camera shows the house for the most part well insulated. I just have alot of windows, so my design BTU is pretty high. I calculate it at 45K/hr max design load. SO I am looking at a 130-140K Gasifier, with 250-800gal of storage. I will have a combination of radiant loops, Forced air exchanger and some type of DHW. DHW need a back up, and the house back up will be the original Nat gas forced air furnace. So my issues for storage are I have a 32" wide door with a pretty big jog to get down in the basement, so for storage my options are 1) unpressurized storage in basement 2)multiples of 250gal pressurized tanks in basement 3)outdoor storage pressurized super insulated R45+ 4) combination of indoor and outdoor pressurized storage I would like to at some point in the future add a homemade solar loop, so I need to keep options open for that. In my calculations I am looking to have roughly 750gal pressurized storage or 800 unpressurized, so I can achieve 450K BTU if I run the temp of the tank all the way down to the lowest primary heat being the radiant loops. 800 unpressurized or 3 250gal propane tanks in my basement seems to take up alot of space I dont want to give up. So the option I am trying to entertain is a 500gal propane tank under my tall outdoor deck. I have roughly 45" clearance and plenty of length, and could dig down a little if needed to get it in place. I have a huge supply of polyiso 3" panels that I can insulate with, and will blow the odd shapes with 2 part poly foam when I get my attic walls redone. The tank would be separated roughly 20-30 feet from the boiler. Would it be feasible to put 500 outside, then have a primary 250gal inside that will heat first, and maintain usable heat for the DHW and forced air exchanger while the outside tank heated up slower. Is my diagram logical how I have all the parts plumbed in?