The remarkable successes with the gassification boilers are numerous and adequate testimony to the tremendous advances in technology in this area. "You’ll have to give us some details of your flat plate hx for charging the tank, Jim." Mine may be a little unique, but I think the concepts should be transferable to other areas. My installation is inside my wood-working shop, including boiler and steel storage tank. All heat, except for that which goes up the stack, stays inside. Think of the hx as a single heating zone or heat load. The boiler simply has a short circular loop to the hx and return. This is pressurized, with expansion tank, air scooper and vent. I use the Tarm recommended Termovar load mixing valve, so really no hot water moves to the hx until the Termovar starts to open. On the return side, or outlet side, of the Termovar, I have a surface mounted line-voltage aquastat set at 150. Until this aquastat closes, water is moving by gravity feed from the boiler supply, through the Termovar, and return to boiler. No water is moving through the hx. As soon as temp hits 150, the aquastat closes and turns on the boiler circ pump and a second circ pump on the other side of the hx. Both pumps always operate at the same time. Hot water now moves through the boiler side of the hx and transfers heat to the output side of the hx. The output side of the hx is non-pressurized to the steel heat storage tank, with expansion space left in the top of the tank. Cold water from the bottom of the tank is received by the circ pump and pushed throught the hx, returning hot water to the top of the storage. I have no separate heat control or thermostat on the storage. It takes all the heat the boiler can deliver. If by chance storage heats to boiler output capacity, the boiler simply will reach 190, and cycle off and on based on boiler controls. Never-the-less, so long as return temp to the boiler is 150 or above, both circ pumps will continue to operate. I have never reached a situation yet where water drawn off the bottom of storage has been above 150. Due to stratification, water at the top of the tank often exceeds 150 though. I am getting all the heat I need with this level of heat storage. As mentioned in prior post, there is a diverter valve on the output of the hx to immediately divert hot water to a unit heater and then back to storage input. The unit heater does not strip all of the heat out of the water. The unit heater fan is operated on a thermostat to provide heat as needed. A unique aspect of my steel storage, since it is interior to my shop, is that the tank now operates as a large radiator, and once the water is heated I rarely need to use the unit heater. In fact, the heat radiation from the tank has been more than needed, and I have wrapped an insulation blanket around the top, bottom and 3 sides of the tank to limit radiation only from the front. No fan/electricity needed for normal heat. Sizing of the hx was not too engineered. I started with a 20 plate 3-1/2 x 8. It was adequate, but the boiler delivered far more heat than this hx could strip, so the boiler regularly cycled off and on. I now have a 30 plate 5 x 12, 1" inlets and outlets. This does have the capacity to take all the heat the boiler delivers, actually more, and I am very satisfied. My boiler circ pump is a used Taco 009 which I had on hand, and the output side to storage circ pump is a Taco 007. I am aware of the corrosion issue with this pump on the open non-pressurized storage side, but for the cost of this pump and steel tanks, what the heck. The only remedy for corrosion, and just to provide some protection for the hx, is a high temp water filter (50 micron) on the supply side from the tank to the hx. This filter needs to be changed every week to 10 days, and it is usually is full of a rusty slime which I suspect is coming from the steel tank (a used fuel oil tank). I am quite certain I will install a 1200-1600 gallon buried, insulated concrete septic tank next summer for storage. Should eliminate corrosion problems of any significance and provide heat for a week or longer for my shop with no boiler firing. Hope this helps.