[jotato]

> It's a simple matter, therefore, to calculate the CO2 and financial cross over point for a heat pump vs. a furnace. I did that calculation when I had one installed in my house (for ductless AC; heating is an added bonus). It's somewhere between about -5 or -10 C, if I recall correctly.

How can I do this? I know my heat pump can only maintain (not raise) my house temp at 36F/2C. But I have yet to figure out at what temp it is cheaper to run my natural gas furnace. I suspect ~40F/5C but that is just a guess (see my comment on parent)

[thsksbd]

Simple in the sense that high school chemistry/math is all you really need + definition of COP. Its a few steps.

1. You need to get your pump's COP vs T from the manufacturer. This is the hardest part.

2. Now find out what chemistry is used for your mains power (nat gas, coal, etc).

3. Assume (or get) the efficiency of your furnace as COP = 0.9

4. Calculate for each delta T how much input each heating Joule of energy takes both methods.

5. Calculate the cost of each Joule for each method at each T. If you are charged electricity based on consumption, use the marginal rate.

For CO2 emission:

6. Apply the appropriate generation/transmission loss for electricity.

6. Calculate the CO2 from chemistry.

[jcalvinowens]

The manual for mine just gives two COP values: 3.63 at 47F, and 2.44 at 17F. That puts the cutoff for me at 30F, which is absolutely as cold as it ever gets in the bay area, so I only have the heat pump.

This is a longer explanation I wrote up when I replaced it: https://www.reddit.com/r/bayarea/comments/10lxyso/replacing_...

[bobchadwick]

If you happen to have an ecobee thermostat, https://beestat.io/ is an amazing tool for figuring out how your system performs.

[jotato]

I don't :/ I do have a smart home setup but it is local-only. I think I am capturing most of the data I need.

I know when my HVAC is running. I know how much power it is using. I know the temperature of every room, I have a stat outside so I have realtime temp/humidity of my location...I just don't have a way to capture and record how much heat is being generated. I'm wondering if putting a temperature sensor directly on an air vent would let me capture it over time