I have a Triangle Tube Series 50 (45 gal.) in a 2,000 sf house with 2 bathrooms. My plumber said I should put in a smaller unit and I wanted a bigger one. We compromised on this unit, because he said a bigger one would consume a lot more energy. I take a 25 min shower with a 5 gpm shower head, and I get enough hot water from this unit, but it took some doing. The first thing I would suggest is to turn the temperature on the water heater all the way up. We have an L-shaped ranch with the water heater on one end of the house, and the master bath on the other (over an unheated crawl space). So we need to keep the water very hot to get enough hot water at the bathroom. The hotter the water is, the more cold water you'll mix in, and the longer your hot water will last. Despite this, I was still running out of hot water after about 15 min. As my shower valve doesn't have a volume control, I put a small valve on the shower arm which allowed me to slow down or shut off the water when I was soaping myself. This allowed the hot water to recover a bit before I finished my shower. The real breakthrough came last summer though, when I had a new boiler installed. The installer told me that the circulator pipes between my boiler and water heater were only 3/4", when they should be 1 1/4". He also set up the new boiler so that the water heater gets priority over heat to the house, and the boiler automatically heats up to 180 degrees whenever the unit calls for more hot water. Now I have plenty of hot water for a 25 min shower followed by a shave, even without turning the volume of hot water down during my shower. I think you should be able to get enough hot water out of this unit provided you use it to its full capacity. You may need to have someone do some work on your boiler though. One rule of thumb I live by, is to never let a contractor tell me how much water or hot water I need. Aside from this, do you have separate shower valves for your 2 shower heads, and are you satisfied with the water flow? Many newer shower valves limit the flow to 2.5 gpm or less. You can check your actual water flow with a 2.5 or 5 gal bucket and a stopwatch. If you're getting enough flow out of the shower arms, but not out of the shower heads, there are some places that sell shower heads with easily removable flow restrIctors.

Three additional points about power outages and gas water heaters. First, since standing gas pilot light models were phased out years ago. Power outages will affect conventional (tank-style) gas water heaters the same as on-demand models (a/k/a tankless) models and hybrid gas models (smaller tank combined with on-demand capabilities). They all need household electrical power to run their ignitors. Second, the water slowly cooling water in the largish (30 to 50 gallon) tank on a conventional model might give you reservoir over a few hours. Adding solar water heating panels on your roof could extend that. But, you can add a solar water heating system to use with a tankless water heater, too. Third, you can get a battery back-up (a/k/a uninterruptible power supply or "UPS") to run pretty much any kind of gas water heater for a time. I know several folks with basic, conventional/tank-style gas water heaters --- no power vent fan, no recirculation pumps , no "smart" features --- who claim they can get hours of operation from even ordinary computer UPS units. There are higher capacity UPS units made specifically for running on-demand/tankless models with vent fans and such. Rinnai, for example, recommends a wall mountable model called a "HUGO" for use with its on-demand heaters.

When we lived in Canada our home was what was called a tri-lvel. You could enter from the garage or the front door to a small foyer with closet and then you went either up about 7 steps to the living room/dining room and kitchen or down to the family room 7 steps. Once up the 7 steps to the main floor you could turn to the left and go up another 7 steps to the 3 bedrooms and bath that were built over the garage. This was all on a relatively flat lot. No lot elevation needed to make it work. Right now we live at the beach in the South in what is known as a reverse floor plan. Two single car garages, a family room and two bedrooms are on the ground level. The two single garages open to a center hallway downstairs. Family room behind one garage, and two extra bedrooms and a bathroom behind the other. You go up a full flight to the main level with living/dining/ sunroom and 3 bedrooms. We are hoping to start a new build soon, a block further back than we are now, out of the flood zone, so we can come into our home and yard on the ground level. Well, it will be elevated two feet, but close enough. As a younger person the stairs into the house never bothered me that much although lugging groceries is always a pain, but I mostly miss being able to just walk out into our backyard for a bit and then back inside without having to climb a flight of stairs, or just even viewing our yard from the indoors.

100' of 3/4" PEX pipe holds about 1.8 gallons of water. You would have to run a bathroom sink almost 2 minutes before it would start to get warm. A small electric tank heater VERY near (In) the bathroom would provide nearly instant hot water to the sink for washing your hands or shaving. The link is to a 6 gal unit. These small units are slow to recover, so you want enough storage to take care of hand washing, etc. At 6 gallons it will also have enough storage to buffer the initial almost 2 gallons of cold water in the pipe when you are taking a shower until the hot water from the main unit takes over. Electric resistance is the most expensive way to heat water. However, a small point of use heater in series with a gas tankless or electric hybrid would save both energy and water when the main heater is far from the master bath. Copper pipe has a slightly larger inside diameter than PEX. That same 100' of 3/4" pipe in copper would store about 2.5 gallons of water instead of 1.8 for PEX. In addition to the water in the pipe, the thermal mass of pipe has to warm up, and then if it's not insulated and in a slab (not code) the copper is going to conduct the heat more readily to the concrete than PEX. For those reasons I'd say copper will take longer to get hot water than PEX. I want to again say that the best solution is not to have a water heater 100 feet from where the water is being used. Be sure to insulate the hot water line in the slab to R5 - not the R3 pipe insulation you find at the hardware store.