A 1/5th or 1/4 HP chiller is probably enough. I don't know if any brand is more efficient than any other, but I suspect they are all comparable. Make sure that you keep the cooling fins of your chiller clean (don't let dust build up on them) and put the chiller where it has lots of cool air to pull in and can blow out how air without recirculating it (i.e.: don't put it inside a stand) To save money, you need to minimize the amount of heat that gets into your water, and must then be removed by your chiller. To do that, you need to understand how heat gets into your water: 1) Pumps and lights. The heat generated by any electric motor, needs to go somewhere. With a submerged pump, all of it goes into your water, with an external pump, most heat goes into the air around the pump motor, so use external pumps if you can afford them (I buy used Iwaki pumps, and blow a little fan over them to keep them cool). Don't use lights that add heat to the water. I use a single fluorescent tube, raised above the top of my tank on little insulated spacers a few inches so that very little heat comes off of them into the water. LED lights might even be better. 2) Assuming the room air is warmer than the tank water, heat gets into your water through every square inch of surface area that has tank water on one side, and room air on the other. There are three ways to minimize this heat conduction: A) Have the room temp as close to the target tank temp as you can. If you can keep the room temp below 72 (might require AC, which also costs electricity) and decide that 65 is cold enough for your bimac, you only have a 7 degree difference. That will be easier to do than a wider difference. B) Minimize the surface area that touches cold water. A 60 gallon rectangular tank (48x12x24) has 20% more surface area than a 60 gallon cube (24x24x24). A separate sump adds a lot of surface area. I desingned my tank with a dividing wall, so that the left 20% of the tank is the "sump", and the right 80% of the tank, is the tank. Water overflows the dividing wall, and there is no external sump. That saves the cold surface area that a sump would add, plus the surface area of any plumbing required between them. I also made all the plumbing runs as short as possible. C) Insulate any cold surface as much as possible. This will slow down the rate at which heat can get through the surface and into your water. Use pipe insulation around all plumbing (with wire ties keeping the ends tight over the pipes). Use 1" thick, or thicker rigid Styrofoam insulation panels on each flat surface that you don't need to see through. My tank rests on a 2" thick piece of Styrofoam, and I've covered one side and the back with a Styrofoam sheet (wrapped in black vinyl to look nice). Acrylic is a better insulator than glass, so an acrylic tank, especially a thick one, will use less electricity than a glass tank. If you are an ambitious do-it-yourselfer (like me) then you can add spacers, and a second pane of glass, or acrylic, to the uninsulated front, and side(s) of your tank to create a 1/4" to 1/2" airspace. That will also save a lot of electricity, and ensure that you never get any "sweating" (condensation). Insulation You can insulate the tank by covering the bottom of the tank (on the outside), the back, and maybe one or both sides with anything that heat has a hard time passing through. If you plan to use a sump, on e possible trick is to use a plastic ice chest, instead of a glass or acrylic box, as your sump. For the tank, I've tried a few options: 1) Styrofoam brand insulation board. You can find it at home improvement stores or lumber yards in various thicknesses. I usually buy 1" thick, use 1 layer for one side of the tank, and one or two layers for the back. I use 2 layers for the bottom of the tank. You can measure and cut it to size with a hand saw, or power saw. It's blue, and not very attractive, so I usually go to the fabric store and buy a couple yards of black vinyl (cheap) to wrap each cut piece of Styrofoam in, like a present, using black duct tape. You can even sew the vinyl to make a custom fit cover for a cut piece of Styrofoam. Attach it to the tank back and side(s) using adhesive Velcro (sew the Velcro to the vinyl, and stick it to the glass) or black duct tape. cut a piece to fit the bottom of your tank, and place it between your stand and your tank (it can easily support the weight). If your tank is already full, you can still attach Styrofoam to the exposed parts of the bottom, or to the underside of the wood your tank rests on. Actual Dow Styrofoam brand insulation sheets are rather stiff, and so work well for glass tanks because they don't bow. the walls of acrylic tanks bow out a little, so you'll need to use generic (usually white) styrofoam (not Styrofoam brand) that are a little bit flexible. 2) Fiberglass insulation, like for an attic, or a water heater blanket, or Polyester batting (like they use to make quilts - from the fabric store) You would need to make a cloth cover, like a big pillow case, put a layer of insulation into it, and then find a way to attach it to the sides, back, and bottom of the tank. The front and maybe one or both sides of the tank are still uncovered, and letting a lot of heat in, but it's a lot harder to insulate transparent surfaces. Using an acrylic tank is a little better than a glass one, but to really insulate transparent sides, you need to glue a 1/4" to 1/2" spacer along the edge and attach a second pane of glass or acrylic, to create a sealed air space between your tank, and the new sheet of glass or acrylic. This is difficult to do correctly, but I've done it, and I've learned a few tricks. I'll write up the method if anyone ever feels ambitious and wants to try it, but that's another (long) post.