It's prohibited for one. And for two, to actually run an electric tankless will require most of the power that you currently have in your panel. 125-200 amps are needed. If you live in a cold climate, electrical is not really doable at all because of the incoming winter water temperature. Gas tankless is much easier to retrofit, and even it may require new gas service for the home.

Kats_Meow, I'm in TX, SW of Houston. I'm on a private well, semi-rural area at edge of my town. My pump tank is in my (detached) garage. My well and (submerged) pump is wayyyy around on the other side of the property due to logistics and requirements of sufficient space for both a well and septic, so it's a long (but underground) run from the pump to the tank. During the occasional cold snaps like this past winter, incoming water temp can drop to less than 40°F. In heat of the summer it may be 80°F or a tad more. My electric tankless is a 120amp unit. It doesn't have any problem generating 135°F to 140°F output when I (occasionally) want that high a temp for washing a load of whites. Otherwise I set the tankless at 100°F to 102°F in summer, 104°F in winter for normal use. That low temp is fine for dishes, my dishwasher has on-board heating and can work with a cold input. My tankless unit varies its power draw per the input temp, output temp, and flow rate. It may operate at little as 5% of full power or at 85%+ ... so obviously it doesn't always pull 120 amps, but the circuit must be able to supply full power when needed.

To achieve 4 GPM at 60 temp degree rise it with require about a 30 KW unit. Which should be adequate for two 2.5 GPM showers set at 105 degrees. At 240 volts (most homes have 215-230, so even less output) it will take 120 amp service alone to heat the water, even on a 200 amp service, doesnÂt leave you enough to run heat pump, dryer, range/oven and lighting. In addition you mention turning off gas at furnace so will you be adding more electric coils to the ductwork for when the heat pump canÂt keep up when itÂs cold out? If you hate gas that much, install a 60 gallon plus electric water heater, pull furnace and install air handler with electric resistance back up heat, and then complain about the high energy bill while the rising electric costs continue to climb since they are closely tied to Nat gas costs because of production. Most people donÂt have a concept of how much input or energy is required to heat water with electric, especially on-demand units. Look at the gas units, instead of a 40 gallon tank with 40,000 BtuÂs the gas on-demand units are 200,000 BtuÂs to meet the draw demand.

city Agree that there is something not right about the kitchen and laundry room. I would have the plumber check if there are anti-scalding valves on the fixtures. When we first moved in, I had to adjust these to properly work with the tankless units. The problem was that out of the box, the fixtures were set with too much cold water in the mixture, and it took forever for the hot water to overcome the cold water mix. At 15 to 20 feet away, the delay should be less than 10 to 15 seconds or so. The master bedroom is another story. I would check anti scalding valves in the master bath and adjusting those might help a little. But you still have 70 feet of water to push out of the way. There are other solutions besides the water recirculating system: - use small point of use hot water generators underneath each master bathroom sink. If your main issue is getting hot water to the sinks (and you don't mind waiting a little for the tub or shower) then the point of use systems can fix that. They make several types - both tank and tankless. The downside is that you need to run seperate power to those units, but it might be a lower cost option in the long run (see my note below on recirc loops). I have one of these under my butler pantry for generating hor water for tea and it cost 140 dollars for the unit. - If you have 2 Rinnai units, perhaps move one of them to the side of the house where the master suite is. The closer you get the hot water source to the master suite, the faster you will get water. This may not be possible since venting the unit if it is gas can be a challenge. - Add a small high efficiency hot water tank on the master suite side of the house to fee the sinks and shower (let the tub remain fed by the tankless). You can get a small tank sized for your daily sink and shower needs. Then you have the recirculating system option which requires a small tank (4 to 10 gallon electric or gas tank), a small pump, and all lines in the recirculating loop to be insulated. The small tank must be sized properly - not just the amount of gallons it holds but the heating element size - or the system might not work properly. You also have to realize that your monthly energy costs will go up because you must keep the pump running during the times when you need hot water. The cost to run the pump is relatively low - pennies per day - but the cost to keep heating the water as it cools when looping can be significant. If you do go down the recirc loop route, get a pump that has a 2 timers on it. Then you can set the timers for morning and evening use, but turn the pump off when hot water use is not expected. The tank remains enegergized all the time - and turns on based on a thermostat - to keep the water at the set temp but since the water is not looping when the timers are off, the amount of energy required to keep the hot water in the tank hot is minimized. I would find a good plumber who can give you an independent evaluation for solving your issues. It sounds like the builder just wants you to throw money at the problem and that might not be the best way to handle it.