If there is one thing that you will learn from making hypertufa is most of what you learn is from trial and error. Most likely no one knows how much you need ( as a result no quick reply) because all the forms are different sizes. Your post did not indicate how big the box is for your mold. Take a coffee can and measure each ingredient. Log in in a notebook for later reference. Experience will teach you to have a smaller second mold ready for any excess. Or make small tufa balls, then flatten then and they will become feet for your containers. Good luck, take pictures and post you results Mike Here is a link that might be useful: My Blog

Start with the uprising effluent velocity of around 3 ft/s or 180 ft/min, multiply by the hood aperture area in square feet. This is the air flow (cfm) required to capture and contain the cooking plume that is intercepted by the hood if the surface the rising plume meets is relatively flat and horizontal. With less velocity, some effluent may "reflect" (curl) out of the hood. For pyramidal hoods, usually sold with baffles, the interior reflection angle is predominantly upward, and this allows the cfm to be less because some of the effluent momentum is still carried upward after the first bounce. One might get away with a factor of 0.5 on the product of aperture and plume speed. For example, a 6 square foot baffled hood of the pyramidal style (e.g., commercial, Independent, or ModernAire baffled hoods), would require around 540 cfm (actual). Please consider that due to various duct pressure losses, hood pressure losses, and house negative pressure, the actual flow rate that a particular blower can move will be significantly less than its rated (at zero static pressure) flow rate. So, a four square foot hood would require 2/3 of the above calculated value, or 360 cfm. But to make up for the losses, the blower should be rated perhaps as much as 1.5 times larger to actually move 360 cfm. C.f. Blue Star's choice of words: "... move a minimum of 300 cfm." Please consider all these values nominal, and dependent not only on many factors not accounted for here and rarely specified so that they can be accounted for, but also on user tolerance for odor, type of cooking, etc. kas

Sorry ribs1, you're caught in a situation many of us don't face and I surely empathize with the expense of conditioned Make Up Air (MUA) due to code. I read the OP asking about Blue Star BTU and venting CFM's. MUA is increasingly considered and discussed when re-doing or building a kitchen, and should be discussed pre-purchase of a pro-range. MUA has been an active topic of interest here on GW as well as on greenbuildingsdesign.com in "Makeup Air for Range Hoods" (linked below) and on many HVAC forums. Good reading and sources for solutions for industrial conditioned MUA (which perhaps will help you somehow too ribs) are also found on http://www.greenheck.com. MUA, passive or active, is available without excessive expense for most of us as we are not restricted, as yet, by specific code requirements. I'm firmly in the camp of matching one's cooktop/range purchase to one's budget for proper ventilation and MUA and more to avoid any risk of acute illness/death due to carbon monoxide poisoning from lack of replacement air. Here is a link that might be useful: Makeup Air for Range Hoods

As long as your hood vent works properly, there is no need for another vent.