First some background on the house: it is in California where energy costs have soared. It has three floors, per our building department. (It‚Äôs really on a hill and since we‚Äôre converting the basement, more than half under ground, into living space, it is considered a floor, I‚Äôve digressed.)
We have three and a half bathrooms, a washing machine, and a kitchen with a couple of sinks and a dishwasher. The kicker is the large master bathtub and a multi-head shower. (Sounds decadent, but we‚Äôre going for broke, literally.) With all of this, we‚Äôve calculated needing two larger units: one in the attic and one in the ground floor mechanical room where the furnace is located. In reality, based on our likely usage, we‚Äôd never need this kind of horsepower, but, since there are so many bathrooms and sinks, a future owner, clearly absent any common sense, may need to run so many appliances at once.
As for brands, I had honed in on the Rinnai version until I discovered that their venting system is proprietary and runs around $35 a foot. (Ouch.) This isn‚Äôt an issue for the attic-mounted unit, but the one in the basement mechanical room needs a 45-foot vertical rise to clear the peaked roof. (Quick math says that vent will run more than the unit.) I could put both in the attic, but that means running water lines back down to the basement level and running the taps until it arrives. (Seems to me like it defeats the energy saving advantage.)
So I decided to look at the Takagi units, which can use standard b-vents. Problem here is that they are limited by a 35-foot vertical rise in the vent. (This problem may also exist in the Rinnai, I haven‚Äôt checked.)
Now, even if I can work around the venting issues, perhaps by putting both units in the attic, the local utility company wants me to install a 2-inch service because ‚Äúin theory‚Äù all of the gas appliances could be on at once and demand would exceed my inch-and-a-half service. Argh! (To their point, the btu draw of the tankless units is around 180,000.)
So, if you‚Äôve made it this far, thank you for indulging me and here are my questions: is the Takagi vertical rise limit a hard and fast rule? Can I push this and will I be all right? From personal experience, are people finding that running the tap to get hot water through ‚Äúmiles‚Äù of piping takes a long time and wastes energy? (I‚Äôm thinking of putting them in the attic in this case and I know this isn‚Äôt good for water usage, but focus on the energy.) What‚Äôs the risk of having an undersized gas line besides the fact that I won‚Äôt be able to cook for the entire population of Texas while they‚Äôre showering for dinner?
Any feedback is welcome.