PG&E Minimum Bill Charges for Gas or Gas + Electricity Together?

[Redhill_qik]

Where do you live and how long have you had the Rheem hybrid? Like any heat pump, its COP and how much heat it can deliver dramatically depends on the difference in temperature (another reason I'm not a fan of ratings that show a single BTU/hr or COP value or whatever the units are any more than single mpg or Wh/mi values that assume you're always driving in specific conditions at a specific speed). The 4200 BTU/hr rating was likely measured under the standard test conditions:

I have had my Rheem PROPH80 T2 RH375-SO 80g UEF=4.0 since early October. It is installed in my garage and is set to heat to 138F with a mixer that takes it back down to about 128F. I also have a recirculation system with an Alexa controlled plug for the pump that we can give a voice command to run for 2 minutes prior to getting in the shower. With the following real world results:

Date​	Monthly Total kWh​	Monthly Average kWh/day​	Cumulative Average kWh/day​
10/31/21	69.33	2.89	2.89
11/30/21	69.51	2.32	2.57
12/31/21	93.66	3.02	2.74
1/31/22	87.18	2.81	2.76
2/28/22	64.06	2.29	2.66
3/31/22	65.81	2.12	2.57
4/30/22	66.78	2.23	2.52
5/31/22	52.92	1.71	2.41
6/30/22	51.08	1.70	2.33
7/31/22	49.01	1.58	2.25

Worse case was in December with the colder ambient temperature and six people in the house instead of 2. I set the controls from Energy Saver to High Demand when we had 6 people in the house, but the logs don't appear to show any electric element usage during that time. Nor have I seen this at any other point even after filling a bathtub with 65 gallons of water.

I went from using 29-32 therms/month during the summer to just 2-3 therms/month for a savings of about 28 therms/month with a hotter water temp (I had turned it down trying to reduce costs). During the summer, the baseline is only 0.49/therm per day or 14.7 therm/month. So 11.7 therm at the Tier 1 cost ($1.97953) and 16.3 therm at the Tier 2 cost ($2.44752) which is $63.05. During the winter with gas heat all of the savings would be at the Tier 2 costs ($2.50 avg for Nov'21-Mar'22) so that would be roughly $75.00/month. I expect to save $815/year in gas costs with a reduction in my net exports of 850 kWh which at $0.088 (SVCE NSC is twice PGE NSC) is worth $74.80 for net savings of $740/year. After a $2,000 rebate from SVCE for switching from gas to electric hybrid I will pay off the installation cost in under 5 years.

 

[STS-134]

I have had my Rheem PROPH80 T2 RH375-SO 80g UEF=4.0 since early October. It is installed in my garage and is set to heat to 138F with a mixer that takes it back down to about 128F. I also have a recirculation system with an Alexa controlled plug for the pump that we can give a voice command to run for 2 minutes prior to getting in the shower.

Did you have this "on demand" recirc system, prior to getting the HPWH, and use it in exactly the same way?

With the following real world results:

Date​	Monthly Total kWh​	Monthly Average kWh/day​	Cumulative Average kWh/day​
10/31/21	69.33	2.89	2.89
11/30/21	69.51	2.32	2.57
12/31/21	93.66	3.02	2.74
1/31/22	87.18	2.81	2.76
2/28/22	64.06	2.29	2.66
3/31/22	65.81	2.12	2.57
4/30/22	66.78	2.23	2.52
5/31/22	52.92	1.71	2.41
6/30/22	51.08	1.70	2.33
7/31/22	49.01	1.58	2.25

Worse case was in December with the colder ambient temperature and six people in the house instead of 2. I set the controls from Energy Saver to High Demand when we had 6 people in the house, but the logs don't appear to show any electric element usage during that time. Nor have I seen this at any other point even after filling a bathtub with 65 gallons of water.

I went from using 29-32 therms/month during the summer to just 2-3 therms/month for a savings of about 28 therms/month with a hotter water temp (I had turned it down trying to reduce costs). During the summer, the baseline is only 0.49/therm per day or 14.7 therm/month. So 11.7 therm at the Tier 1 cost ($1.97953) and 16.3 therm at the Tier 2 cost ($2.44752) which is $63.05. During the winter with gas heat all of the savings would be at the Tier 2 costs ($2.50 avg for Nov'21-Mar'22) so that would be roughly $75.00/month. I expect to save $815/year in gas costs with a reduction in my net exports of 850 kWh which at $0.088 (SVCE NSC is twice PGE NSC) is worth $74.80 for net savings of $740/year. After a $2,000 rebate from SVCE for switching from gas to electric hybrid I will pay off the installation cost in under 5 years.

What's the 2-3 therms/month for? I'm assuming a gas stove? My usage typically hovers around 8-15 therms/month during the summer time, when I'm only using gas to power the water heater and nothing else. In a "typical" summer month, it's probably $15-20 worth of gas charges. I'm wondering if something was wrong with your old water heater or if you just had a lot of people taking showers.

 

[Redhill_qik]

Did you have this "on demand" recirc system, prior to getting the HPWH, and use it in exactly the same way?

What's the 2-3 therms/month for? I'm assuming a gas stove?

The recirculation was updated during the installation and there was some thermal siphon behavior going on with the loop functional even if the pump was unplugged. I tried turning off the valve for a short while to kill the loop and the monthly total went down to 24 therms. However, this was not acceptable to my wife as the water took way too long to get warm in the primary shower on the 2nd floor, plus the extra wasted water down the drain. So maybe about 4 therms/month was related to this issue. The original was Bradford White 75gal that was probably not well insulated and was constantly bleeding heat.

The 2-3 therms/month that I am seeing now are for a gas cooktop and a gas dryer. The built-in dual oven is electric.

 

[STS-134]

The recirculation was updated during the installation and there was some thermal siphon behavior going on with the loop functional even if the pump was unplugged. I tried turning off the valve for a short while to kill the loop and the monthly total went down to 24 therms. However, this was not acceptable to my wife as the water took way too long to get warm in the primary shower on the 2nd floor, plus the extra wasted water down the drain. So maybe about 4 therms/month was related to this issue. The original was Bradford White 75gal that was probably not well insulated and was constantly bleeding heat.

The 2-3 therms/month that I am seeing now are for a gas cooktop and a gas dryer. The built-in dual oven is electric.

The math is still not working out. 100000 BTU is equivalent to 29.3 kWh of energy. There are 100000 BTU of heat, or 29.3 kWh, in a therm of natural gas. You had been using 29-32 therms/month prior to making the switch. Subtract off your 2-3 therms/month for the gas cooktop and dryer and your water heater must have been using approximately 28 therms/month. That's 28*29.3=820.4kWh worth of energy. Now, gas water heaters, especially the ones with draft hoods, which most people have, are grotesquely inefficient, and only about 60% of the energy they use goes into actually heating water. So of the 820.4 kWh of heat energy in the gas, about 820.4*0.6=492.24 kWh goes into actually heating water. That's still about 16-17 kWh/day though. Now you're telling me that getting a heat pump water heater has reduced your heating requirements to 2-3 kWh/day, or about 80%? I mean, gas heaters with draft hoods are leaky, but I don't think they're anywhere near THAT leaky.

Let's assume that your actual requirements for heating water are 3 kWh/day and the old heater was leaking 13 kWh/day into your garage. That is equivalent to a standby energy loss rate of 541 WATTS (on top of the 40% of the initial heat energy that goes up the flue and never goes into the water in the first place).

 

[Redhill_qik]

The math is still not working out. 100000 BTU is equivalent to 29.3 kWh of energy. There are 100000 BTU of heat, or 29.3 kWh, in a therm of natural gas. You had been using 29-32 therms/month prior to making the switch. Subtract off your 2-3 therms/month for the gas cooktop and dryer and your water heater must have been using approximately 28 therms/month. That's 28*29.3=820.4kWh worth of energy. Now, gas water heaters, especially the ones with draft hoods, which most people have, are grotesquely inefficient, and only about 60% of the energy they use goes into actually heating water. So of the 820.4 kWh of heat energy in the gas, about 820.4*0.6=492.24 kWh goes into actually heating water. That's still about 16-17 kWh/day though. Now you're telling me that getting a heat pump water heater has reduced your heating requirements to 2-3 kWh/day, or about 80%? I mean, gas heaters with draft hoods are leaky, but I don't think they're anywhere near THAT leaky.

Let's assume that your actual requirements for heating water are 3 kWh/day and the old heater was leaking 13 kWh/day into your garage. That is equivalent to a standby energy loss rate of 541 WATTS (on top of the 40% of the initial heat energy that goes up the flue and never goes into the water in the first place).

All of the numbers are coming from my historical PG&E bills for the therms/month and the Rheem app for the consumed kWh. I don't have any reason to distrust that the current sensors and log data for Rheem are inaccurate.

My original water heater was a Bradford White URG275H6N and the data sheet shows that the Uniform Energy Factor is 0.59 versus the Rheem with a 4.0 UEF. This is a factor of 6.78 more efficient. As I mentioned I probably was losing 4 therms due to the thermal siphoning, but let's call that 6, so the equivalent becomes 22 therms. Using your numbers 22*29.3=644.6kWh and with a factor of 6.78 that becomes 95 kWh/month or 3.06 kWh/day. This is pretty close to on target for my worst month in December with 93.66/3.02 kWh. The other months have warmer ambient air and warmer main inlet water temps and require lower energy, some of that is true for the gas water heater, but the ambient air has near zero impact while the effort for the heat pump is greatly improved.

 

[STS-134]

All of the numbers are coming from my historical PG&E bills for the therms/month and the Rheem app for the consumed kWh. I don't have any reason to distrust that the current sensors and log data for Rheem are inaccurate.

My original water heater was a Bradford White URG275H6N and the data sheet shows that the Uniform Energy Factor is 0.59 versus the Rheem with a 4.0 UEF. This is a factor of 6.78 more efficient.

Ah, yes, I was comparing kWh going into the water from gas vs. kWh consumed. But there's a factor of 3-5 efficiency improvement due to the heat pump, expressed as COP. So if you were using 2-3 kWh of electricity, you were actually putting 12-15 kWh of heat energy into the water. I treated the heat pump water heater as an electrical resistance water heater instead of a heat pump.

Is it easy to hear the heat pump when it switches on if you are in the part of the house closest to the garage wall?

 

[Redhill_qik]

Ah, yes, I was comparing kWh going into the water from gas vs. kWh consumed. But there's a factor of 3-5 efficiency improvement due to the heat pump, expressed as COP. So if you were using 2-3 kWh of electricity, you were actually putting 12-15 kWh of heat energy into the water. I treated the heat pump water heater as an electrical resistance water heater instead of a heat pump.

Is it easy to hear the heat pump when it switches on if you are in the part of the house closest to the garage wall?

The noise is only downside for the hybrid heat pump water heater. My model was supposed to have been 49dB which is dishwasher quiet, but I have measured it at 60-61dB which is a bit more than twice as loud at first. I just measured it again and I was getting 57-58dB and have been thinking that it has been somewhat quieter lately. The interior wall next to it measures 39-40dB. We can hear it throughout the house including the 2nd floor, but it has become mostly background noise at this point. I think it was somewhat on par with the gas burner from the original water heater and definitely less than the AC compressor, but it runs for much longer than either of those noise sources.

Rheem supposedly had a retrofit kit that would reduce the noise, but I didn't push for this right after installation and I'm not sure I would get it at this point, probably need to try.

 

[STS-134]

The noise is only downside for the hybrid heat pump water heater. My model was supposed to have been 49dB which is dishwasher quiet, but I have measured it at 60-61dB which is a bit more than twice as loud at first.

Actually, it's not. 10 dB is ten times as loud, and 20 dB is 100 times as loud. A change of +3 dB is double.

I just measured it again and I was getting 57-58dB and have been thinking that it has been somewhat quieter lately. The interior wall next to it measures 39-40dB. We can hear it throughout the house including the 2nd floor, but it has become mostly background noise at this point. I think it was somewhat on par with the gas burner from the original water heater and definitely less than the AC compressor, but it runs for much longer than either of those noise sources.

Rheem supposedly had a retrofit kit that would reduce the noise, but I didn't push for this right after installation and I'm not sure I would get it at this point, probably need to try.

Wow, and it sounds like you have the quieter, older model. And since we live in about the same area, I know how much your AC compressor runs, which is not much. Probably about 1-4 hours a day, mostly in the afternoon, depending on the day, between May and September.