Short of paying a tech to come out, that is. :)

I looked at your three quotes. I am not sure I would want to work with any of these companies. You must have a Manual J load calculation performed in order to properly size the equipment. Any contractor who does not do this is guessing at the sizes. There is no excuse for not doing the calculation. Find a contractor who is willing to do a proper calculation for Manual J and Manual D (duct sizing) calculation. Do you really need two 60 gallon electric hot water heaters? Apart from the massive sizes, why electric and not gas?

s luke: First, if you want to use a silencer, then it goes between the hood and the blower, so an internal blower is out. Use one of many possible roof blowers that can flow the required rate with the pressure loss of the MUA, baffles, and ducts (including effective length increases with turns). Duct pressure loss and length equivalents for turns are on the Internet. (In-line duct blowers are also suitable.) Baffle pressure loss may still dominate if MUA is OK. Put the silencer in the attic if convenient. Note that the diameter is about 4 inches larger than the duct. Joe: There are two separate hood functions to deal with: capture and containment. Capture requires that the hood entry aperture overlap the rising and expanding cooking plumes. This size should be determined for the largest pans that are likely to be used for greasy or odoriferous cooking. Given a resulting hood aperture size, then the issue is containment -- keeping the plume effluent in the hood and ducting to the outside. Every hood is different, and the baffle filters vary, etc., and an exact amount of volumetric air flow (CFM) needed for a given condition has to be determined by experiment or a really complex computational fluid dynamics simulation. (Experiment is less expensive.) It turns out that for most residential cooking where the baffle space occupies most of the hood's aperture area, containment success can be achieved by an air velocity sufficient to entrain the effluent into the air going into the baffle slots. The baffle slot openings are roughly one-half the aperture area, so if the overall air flow is 90 ft/min, then the slot air flow will be 180 ft/min, or roughly the velocity of the fastest plume from a gas fired pan. The link I provided to the Greenheck Guide will lead to a table (page 10, IIRC) with air flow velocities for commercial hoods vs. various cooking processes. The higher velocity cases probably won't apply in a residential setting. But if you want to put a charcoal grill in your kitchen, then they will. The velocity times the hood entry aperture area yields the required volumetric flow rate. This is your goal for actual flow rate. s luke: The duct size is an interesting trade between minimizing duct grease collection (due to impingement in temperate weather and condensation in colder weather) and minimizing pressure loss and noise due to turbulence. Generally, the velocity should be kept between 1000 ft/min and 2000 ft/min. Wrestling 14-inch duct and an 18-inch silencer into place is a lot more effort than 10-inch and 14-inch respectively components. So going larger than minimal is only required in cold climates and/or where no practical blower can handle the required flow rate at the predicted pressure loss. So recursively pick a duct size, calculate velocity, calculate duct pressure loss, check the blower or blowers under consideration for that pressure loss vs. flow rate (on the fan curve or some table). In the process, account for the baffle pressure loss. This also varies with the flow rate and won't be published in general, but it should be safe to allocate 1 inch of water column to the baffles when used at the 90 CFM/sq. ft. hood aperture volumetric flow rate. I am running about 20 feet of 10-inch duct with three turns (about 70 deg, 20 deg, and 45 deg) and a silencer and seem to be achieving more than 1000 CFM from a 1500 CFM blower measured under my Wolf hood (made by Independent ca. 2009). Depending on what combustion appliances are in your house, and whether they have their own MUA or depend on household air, you may for safety reasons need to keep house pressure reduction to -0.03 inches, w.c. Under these conditions, the MUA won't impact the calculation, but will impact one's wallet. Cruder, less expensive passive MUA (even an open window with screen at these flow rates), used where combustion appliance safety is not applicable, could have a good part of a 1-inch pressure loss, and that needs to be accounted for in evaluating the blower. The blower pressure loss is that of the entire loop from outside to kitchen to outside.

If the building code in your area is based on the International Residential Code, your contractor is required to perform heating and cooling load calculations and size the equipment per ACCA manual J and manual S, respectively. Since most areas don't require permits for replacement of HVAC equipment (California being a notable exception) they've probably skipped them. Ask to see the calculations. Then ask the contractor if they'll balance the system so you get the proper air flow to each room.