> every single natural gas water heater is connected to 120V power for the ignition circuit
Mine isn't. During a long power outage, I still had hot water.
I was a bit surprised the water heater was working since I was pretty sure it had an electronic control system. So I went and looked, and sure enough, it was electronic, and somehow the LED was flashing blue like normal!
It turns out the electronics are powered by a thermopile which is heated by the pilot light.
a 1500W heat pump water heater with a COP around 3 will put 5500 watts of heat into the water.
My Rheem hybrid 220v heat pump water heater only has a 500w compressor but puts 1500-2000 watts of heat into the water pulling it from the hot garage.
I have the choice to run it in high demand mode which will run both the heat pump and electric 4500w element for around 6kw of heat into the water if I need fast recovery.
Keep in mind that there's going to be a CoP associated with a heat-pump water heater. Depending on (a bunch of factors) that 1500W HPWH could approach the performance of a 6kW standard EWH.
6.6 kW, for... COP 4, T₁-T₀ = 30 [K] (lower value for warm climate), allowable 30 minute heating time, 50 gallon capacity. A cold climate could double that power requirement, or alternatively double the heating time.
quickthrowman|4 months ago
And for the record, every single natural gas water heater is connected to 120V power for the ignition circuit.
adrianmonk|4 months ago
Mine isn't. During a long power outage, I still had hot water.
I was a bit surprised the water heater was working since I was pretty sure it had an electronic control system. So I went and looked, and sure enough, it was electronic, and somehow the LED was flashing blue like normal!
It turns out the electronics are powered by a thermopile which is heated by the pilot light.
somehnguy|4 months ago
This is incorrect. Multiple homes I've lived in had no electric to the water heater, including my current.
With a standing pilot a thermopile is used to generate the tiny bit of electric required for the control.
SigmundA|4 months ago
My Rheem hybrid 220v heat pump water heater only has a 500w compressor but puts 1500-2000 watts of heat into the water pulling it from the hot garage.
I have the choice to run it in high demand mode which will run both the heat pump and electric 4500w element for around 6kw of heat into the water if I need fast recovery.
tonyarkles|4 months ago
maxerickson|4 months ago
harshreality|4 months ago
kwatts_effective [kJ/s] * heating_time_minutes [min] * 60 [s/min] * COP = 4.184 [kJ/kg/K] * (T₁-T₀) [K] * gallon_capacity [gal] * 3.785 [L/gal] * 1 [kg/L]
6.6 kW, for... COP 4, T₁-T₀ = 30 [K] (lower value for warm climate), allowable 30 minute heating time, 50 gallon capacity. A cold climate could double that power requirement, or alternatively double the heating time.