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HVAC-Heat Pump Discussion moved from here...
...I have another spreadsheet that I use to record HVAC run time, electricity usage, water heater run time, and water usage. I can tell you how much each of my showers cost accurate to within pennies.

Such information helps me identify areas where I may want to conserve or to detect problems. For example, my HVAC run time has experienced a very slight, but noticeable and steady increase over the last seven years that does not correspond with changes in average temperature. I suspect the efficiency of my HVAC system is decreasing over time, but lower electricity rates and more efficient devices have masked the increase in run time. The average person wouldn't notice because the net effect is that the electric bill has remained stable over time, but all the data that I collect and analyze gives me additional insight...
Have you had someone put gauges (or do you own them and already did it) and check the Freon level of the AC of your HVAC? My guess is, it's between 1-3 pounds low.
 

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Have you had someone put gauges (or do you own them and already did it) and check the Freon level of the AC of your HVAC? My guess is, it's between 1-3 pounds low.
I have gauges for R-12 and R-134a, but not R-410a. I suspect you may be correct, but it still heats and cools effectively so I haven't paid much attention to it. I forgot that I have made some tweaks to the heat pump operation (defrost timing, auxiliary heat kW, defrost kW, auxiliary heat lockout temperature, etc.) over the years that result in less dependence on the heat strips and increased compressor run time that I now suspect explains the upward trend I'm seeing.
 

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I have gauges for R-12 and R-134a, but not R-410a. I suspect you may be correct, but it still heats and cools effectively so I haven't paid much attention to it. I forgot that I have made some tweaks to the heat pump operation (defrost timing, auxiliary heat kW, defrost kW, auxiliary heat lockout temperature, etc.) over the years that result in less dependence on the heat strips and increased compressor run time that I now suspect explains the upward trend I'm seeing.
Ahh, Heat Pump, so your using the Freon, year round. I'd still guess your low, which would also mean maintenance would benefit the year round operation. But if you've tweaked the run setup and are using less time/operation of heat strips, then you need to add their reduced operation to the calculations, you might be ahead.
 

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At what temperature does the resistance heat come on with a heat pump?
The answer to that question depends on the size, design, and efficiency of the heat pump and the how the thermostat handles auxiliary heat. The "dumb" Honeywell digital thermostat that came with my "standard efficiency" heat pump activated the auxiliary heat if the indoor temperature was 2ºF lower than the set temperature.

I use a Nest thermostat which adjusts the auxiliary lockout temperature dynamically depending on outdoor temperature, indoor temperature, indoor set point, and system performance. Due to improvements in Nest's software over the years (it was terrible with heat pumps in the early years) and adjustments (corrections) to my system's configuration, I don't recall seeing auxiliary heat use the last two winters - even in temperatures briefly down into the teens ºF. The heat pump runs continuously at those temperatures to maintain the set temperature, but 3 kW continuously is still cheaper than 18 kW cycling on and off.
 
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