ditttohead
Water systems designer, R&D
From a code standpoint a 2.5 cu/ft is not big enough but then again, from a code stand point every single tankless water heater installed does not meet code either. However, code enforcement officials recognize that the chances of exceeding the capacity of either device on a regular basis is slim to none and because of the new energy and water conservation standards that have not yet been fully integrated into the codes, most will allow the installation.
Thanks, perfectly stated. The biggest problem with code and softeners is the minimum flow recommendations of a softener to prevent channelling. That is why we try to limit the systems to no more than 14" for residential, which would give an approximate minimum recommended flow rate of 3 GPM. If we were to do it perfectly, to code, it would require a system 14 design, with three controls, and the tanks would not be allowed to exceed 10" diameter. This would be correct, and to code, but not reasonable nor affordable. Even with 4 bathrooms, 20 GPM peak flow rates is more than adequate for more than 99% of the time. The worst thing that will happen is your softener will produce slightly more than a grain of hardness (hardly noticeable) if you exceed the maximum recommended flow rate. Honestly, do you forsee your family exceeding 15 GPM more than once or twice a year? Especially in states that require high efficiency plumbing fixtures. 2 GPM for showerheads, 1.5 GPM for faucets, 1.28 GPF for toilets, etc. have been the standard in California for many years.
I hope our information is helpful.