I was curious as to how to solve this problem so I did a little research. I think my answer is correct. Changing the configuration from wye to delta increases the voltage across each heater by a factor of 1.73 (square root of 3). The heater voltage becomes: 240V * 1.73 = 416V If you want to dissipate 27KW of total power then divide by the voltage to get the current through the heaters: 27000W/416V = 64.9amps To get the line current through each heater divide the total by 3: 64.9amps/3 = 21.6 The currents from the supply is the summation of the currents in the heaters. The line currents are out of phase by 120 degrees so you need to multiple by 1.73: 21.6amps * 1.73 = 37.5amps Below is a link for a wye and delta calculator. You can plug in any two numbers and calculate the others. Merry Christmas

Here's a diagram of the first story, the only floor with return air vents. (We're working on a plan to add return air upstairs as well.) Each return air duct uses one joist cavity. I'm thinking we could expand each supply run to two ducts in adjoining cavities, put side-by-side vent openings in each set of ducts, and use large grilles to cover the paired vents.

Lighting for a house cannot be designed by mathematical formulas. Doing as internet google searches advise of taking [fc x sf], throwing in a lumen conversion, and you wind up misled and mis-applying the basics. Even sidestepping your calculation errors, your numbers are a perfect example of why you cannot follow these methods. You will need bottled sun and have to wear sunglasses in your house if you continue this path. Take for example your kitchen island of 4'x7' = 28sf. If you want 45fc, that equals 13,500 lumens, or about 12 large, bright 6" recessed cans. How are you going to fit 12 cans over a 4'x7' footprint? Does that sound reasonable? Do you have experience being in a room and have a sense of what works with lighting? Do you notice that the far corner with nothing in it is not "lit" as bright as where you want to read your book? That your dining chair seat does not have to be as "lit" as the center of the table top? You have to understand that talking about fc, lumen, or lux is a theoretical measurement of the consistent spread of light on a defined size of surface. Well, that surface has it's own specific location, it's own characteristics (e.g. reflectivity or physical density around other things), and probably is not concerned with having an exact even distribution of light across it's footprint. And, remember, a light source throws it's light in a wide range of directions, where the light will be more intense at a certain point than others. Don't forget that you will usually have light throws from multiple fixtures overlapping as well. In a kitchen, there is a high variation in the type of actions performed. You can range from 10fc for circulation to 50fc for prepping. You cannot just compartmentalize each function (counter vs floor vs island) and light them individually within the same room. My suggestion is to throw out all you've read about calculations, and start as if you know nothing. Go to this website - David Warfel - Language of Light - to get a feel for what lighting is, what it does, and how it can improve on your life. This website has some really good visual illustrations, which is why I recommend it to people.

kas--thanks!! Appreciate the callout from the old days, and the homework assignments! Sorry for delayed response, was on vacation and elected to ignore kitchen ventilation issues for a week. Super helpful discussion of my issues Issues in my place. Glad that my thoughts on choice of hood and blower seem adequate. As for appliances that are impacted by negative pressurization: two fireplaces: a direct vent in the open family room adjacent to the kitchen, and a conventional wood burning fireplace in the living room, open to the family room Everything else (water heaters, heat pump furnaces) are electric. Locations for MUA air returns are a big question. Since the kitchen is contiguous to, and open to, the family room, there is really no wall space in the kitchen. Ceiling returns would be prohibitively difficult to run up through walls from crawl space. I agree that floor returns are undesirable as catch basins for debris. So I think I'm restricted to low wall returns either in the family room or the adjacent hallway which opens directly into the kitchen without any door. If I read the code cited by CRH above--"into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located"--it would allow discharge into the adjacent hallway. Agree that while code may be primarily aimed at negative pressurization, effectiveness of the actual kitchen ventilation is the point to this entire complex, expensive enterprise, so locating returns properly is critical. Hadn't thought of silencer for MUA, another good thought. Great to have a chance to rejoin this community again for another project. Thanks!