Quote:
Originally Posted by ton80
I believe that Sowtime has identified a key item for consideration of replacing an electric tank water heater with a tankless electric on demand water heater. So far, no other Poster has even mentioned electric power supply as a consideration. I do not believe that you can supply enough electric power to a new on demand water to supply a whole house demand just using the using the existing electric supply to the tank system.
I am not an electrical engineer, but I will try to explain in general principles.
1. A tank system has a typical recovery rate of some 20 gal per hour.
2. A single typical shower uses 1.5 gal/ minute or 90 gal/hour. Shower water is a mix of hot and cold water and depends on the supply water temperature, the desired shower water temperature, etc. For me, a mix of 50/50 seems a good mix. So 45 gph cold and 45 gph hot. Do the math and it does not look possible using only the same electric power supply that the 20 gal per hour tank heater has currently. So the power supply needs to be at least doubled for a whole house setup. My electric panel has 2 spaces for the 220/240 v circuit to the water heater. Sowtime says he needed 4 spaces, so it is nominally double. I know that there are various sizes of breakers and wires but you can check the specifics when you are considering a specific heater.
3. IMHO the quote re Rinnai on demand water heater providing hot water for 4 showers plus other users simultaneously has to be a gas fired heater not electric. I googled Rinnai and found no electric models at all.
4. The electric on demand water heaters such as ecosmart have electric power demands of 18 and 36 kw. 18 000 watts/240 volts = 75 amps required. 36 000 watts/ 240 volts =150 amps.
5. My electric power supply panel has a 200 amp breaker but needs to supply HVAC , stoves etc, when someone wants to take a shower. IMHO, the 18kw model can be possible but not the 36 kw. You still need to check the required wiring to make sure it will be adequate or need to be replaced.
6. NG or propane fired heaters are more suited to on demand systems than electric power units.
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Good point. I'm not an electrical engineer either, but it looks like an electric tankless water heater needs about 4 times the breaker size as a tank type water heater (30 amps vs 120 amps). It may not be possible to add a 120 amp breaker to the existing electrical panel. The panel itself may need to be upgraded to accommodate a 120 amp breaker. Maybe someone else can clarify this.