From HVAC to Heat Pumps - kWh usage

[HardHitter]

Trying to decide if it is worth going from standard HVAC system to heat pump. I'm based in Northern California where temps are mild. Winter mornings hit in low 30s and summer temps hit highs in high 90s low 100s.

With that said, I just got PTO on a a 12kW system with 2 Powerwalls in October 9, 2022. I oversized the system in hopes to be able to cover future usage such as adding another EV. Since PTO on October 9, here has been my monthly electricity:

- October: -487.86 kWh
- November: -530.65 kWh
- December: -18.32kWh
- January: 78.69kWh (usage through January 14)

In total, currently have a -958.14kWh credit.

As you know, California has been storming the majority of December/January and likely explains the low numbers.

I've seen a significant uptick in gas usage to run the furnace in the mornings and fireplace at night.

- October: 26 therms
- November: 64 therms
- December: 110 therms
- January: 26 therms (usage through January 14)

PG&E gas prices seem to be out of control with it being $2.78 - $2.91/therm.

With that behind us, few questions:

- Does it make sense to convert to a heat pump system for California?
- What should be the expected increase in kWh consumption? Based on this, will I still have "excess credit" for future additions like EV.
- Are heat pump systems effective? Meaning, is it sufficient to heat and cool the house to temperatures such as 70 for heat and 65 for cooling?

 

[jhn_]

Yes, yes, and yes.

How much extra kw you use and if there is excess for EV depends on your heating and driving habits.

 

[h2ofun]

Trying to decide if it is worth going from standard HVAC system to heat pump. I'm based in Northern California where temps are mild. Winter mornings hit in low 30s and summer temps hit highs in high 90s low 100s.

With that said, I just got PTO on a a 12kW system with 2 Powerwalls in October 9, 2022. I oversized the system in hopes to be able to cover future usage such as adding another EV. Since PTO on October 9, here has been my monthly electricity:

- October: -487.86 kWh
- November: -530.65 kWh
- December: -18.32kWh
- January: 78.69kWh (usage through January 14)

In total, currently have a -958.14kWh credit.

As you know, California has been storming the majority of December/January and likely explains the low numbers.

I've seen a significant uptick in gas usage to run the furnace in the mornings and fireplace at night.

- October: 26 therms
- November: 64 therms
- December: 110 therms
- January: 26 therms (usage through January 14)

PG&E gas prices seem to be out of control with it being $2.78 - $2.91/therm.

With that behind us, few questions:

- Does it make sense to convert to a heat pump system for California?
- What should be the expected increase in kWh consumption? Based on this, will I still have "excess credit" for future additions like EV.
- Are heat pump systems effective? Meaning, is it sufficient to heat and cool the house to temperatures such as 70 for heat and 65 for cooling?

I get rid on my gas multipack and put in a 10 head, 4 compressor mini split setup. Best thing I ever did, but the reason it works for me is i oversized my solar or I would have been screwed. Meaning, I use like 40 to 70kwh per day just on heating.

 

[brkaus]

To me it’s hard to justify putting in a heat pump if one has a working system. But once the hvac poops out (or us very old) there is no reason to not put in a heat pump with gas backup.

Heat pump doesn’t cost that much more & Gas backup because it keeps the electrical work (cost) at a minimum.

Gives the best of both worlds and you can adjust the lockouts to use more or less gas as needed.

It’s harder to justify replacing a reasonably new fully functioning system.

 

[n.one.one]

Trying to decide if it is worth going from standard HVAC system to heat pump. I'm based in Northern California where temps are mild. Winter mornings hit in low 30s and summer temps hit highs in high 90s low 100s.

With that said, I just got PTO on a a 12kW system with 2 Powerwalls in October 9, 2022. I oversized the system in hopes to be able to cover future usage such as adding another EV. Since PTO on October 9, here has been my monthly electricity:

- October: -487.86 kWh
- November: -530.65 kWh
- December: -18.32kWh
- January: 78.69kWh (usage through January 14)

In total, currently have a -958.14kWh credit.

As you know, California has been storming the majority of December/January and likely explains the low numbers.

I've seen a significant uptick in gas usage to run the furnace in the mornings and fireplace at night.

- October: 26 therms
- November: 64 therms
- December: 110 therms
- January: 26 therms (usage through January 14)

PG&E gas prices seem to be out of control with it being $2.78 - $2.91/therm.

With that behind us, few questions:

- Does it make sense to convert to a heat pump system for California?
- What should be the expected increase in kWh consumption? Based on this, will I still have "excess credit" for future additions like EV.
- Are heat pump systems effective? Meaning, is it sufficient to heat and cool the house to temperatures such as 70 for heat and 65 for cooling?

I'll add something else for you to consider.

Most heat pumps that are dual fuel systems are set to change to burn gas at below about 45 degrees which leads to your increased gas consumption. Newer dual fuel heat pumps can be set to a lower crossover point which means if you have excess kWs you can warm your house with energy from the panels/Powerwalls vs burning gas. Our winters are colder in Georgia and when I replaced my heat pumps a few years ago I went with Daikin and have set the crossover to 15 degrees which will reduce my gas consumption.

Unfortunately I can't report my actual results yet because Tesla is just starting to install systems in Georgia and I won't have mine for another month or so (20 kW solar panels, 4 Powerwalls).

 

[aristobrat]

My area (south-eastern Virginia) had a "once-every-five-years-or-so" cold snap in December that dropped the usual lows from "low 30s" down into the teens for four days, with one day's high only hitting 23.

Based on the number of very angry folks posting copies of their December bills on Nextdoor.com, those low temps appear to have put quite a few older heat pumps into "emergency heat" mode where heat strips were used to produce heat. Kept the folks warm but at the cost of using 8-15 kWh. This doubled some folks bills from the usual $200s into the $400s.

@HardHitter, if you do switch to heat pumps, I'd def. recommend making sure you understand how the system will perform when temp drops below the level where the heat pump can effectively produce heat. In our area, that's usually only a few days every 5-7 years so seems like most folks here opt to take the hit for running "emergency heat" (heat strips) as needed vs. the extra cost of getting a dual fuel (or higher efficiency) heat pumps.

 

[nwdiver]

Yes

 

[RKCRLR]

Keep your eye on Tech Clean California incentives. They are out of funding now but had substantial incentives on heat pumps and they may get additional funding. Dual fuel systems may not qualify for incentives in the future.

I have a dual fuel system and it gets used quite often due to power outages. Heat pumps can really draw down the batteries during a power outage. If you aren't concerned about power outages you'd need to run the numbers to see if the additional cost of a dual fuel system over heat pump only makes sense.

 

[CrazyRabbit]

I got electric resistance heat, NO heat pump; I spend about 400 bucks per year heating my house. So I won’t replace for a long time. I’ve replaced one condenser unit with a 16 seer unit and it saves about 30% on power. I will probably replace the other two, hopefully getting another 20 years on the air handlers. Before replacing the whole system.

 

[theothertom]

You should compare the output temperature of a heat pump vs. gas furnace. Keep in mind that body temperature is 98.6F and anything less than that might feel just warm at best, even though it's at, say 80F. If want "hot" air coming out of your vents, you *might* not want a heat pump.
All I'm saying is do your homework and make sure you know what you're getting.

How Hot Should the Air Be From a Heat Pump

The average temperature output of a heat pump is 85°F to 92°F in heat mode without auxiliary heat. Typically, a heat pump will produce a temperature

homeinspectioninsider.com

 

[CWhite]

Here near Portland OR I am very glad I went from AC/80% gas heat to a Heat pump/95% gas heat. My solar output matches my new consumption and my gas bill dropped over $600 a year. Currently have the crossover temp set to 35. Getting a 2nd EV so adding more solar. Will change the crossover down to 25 to use the extra electricity and use even less gas. Personally I think going to the hybrid system is worth an extra few $1000, give you the choice to use more electricity and less gas or visa versa depending on the current prices.

 

[CWhite]

You should compare the output temperature of a heat pump vs. gas furnace. Keep in mind that body temperature is 98.6F and anything less than that might feel just warm at best, even though it's at, say 80F. If want "hot" air coming out of your vents, you *might* not want a heat pump.
All I'm saying is do your homework and make sure you know what you're getting.

How Hot Should the Air Be From a Heat Pump

The average temperature output of a heat pump is 85°F to 92°F in heat mode without auxiliary heat. Typically, a heat pump will produce a temperature

homeinspectioninsider.com

We like how the heat pump works. Our old gas furnace would kick on and blow 140° air out of the registers for 10 minutes, get the house up to 69°, and then shut off. The heat pump runs at a lower/quieter speed. It does run longer, the heat out of the registers is between 90 and 100° it is less obtrusive, hardly notice it running most of the time. I will tell you that heat pumps do not like big temp swings. If you like the house 10° cooler at night it’s not gonna like try to make up that big of a difference in the morning . As long as it keeps the house at the temp you want not sure why I would care what temp is coming out of the register.

 

[tfan2018]

I have half your panel size and 1 pw and went fully electric. It's enough to cover in my situation, also NorCal.

If your usage is negative in Nov/Dec pre-heat pump then you'll have enough excess energy to transition to heat pump.

 

[brkaus]

Heat pumps do blow lower temp air, but the variable speed setups are pretty good at holding a set temp. Much better than the older ones when heat pumps first became available.

If you keep gas backup, it works great at lower temps.

We have central propane in our neighborhood at monopoly pricing, so straight resistive heat is even lower than propane, but our house didn’t have wiring to the units or even electric capacity in the house for that matter.

 

[arnolddeleon]

The short answer is yes.

I'm in Cupertino and I have heat pump. The original install 17 years ago was dual fuel system with two stage heat pump. When the compressor conked out I replaced that part with a variable speed unit (that operated at much lower temps) and locked out the gas furnace in the configuration. I don't think I've ever noticed the system blowing cold air in the winter for the defrost cycle. I'm a big fan of not noticing HVAC system so I know my system is working well when I don't notice warm (or cold during the summer) blowing. I haven't noticed the gas prices increases. I wouldn't have known about it except for all the people complaining about it.

You can convert therms to kWh, just have to model the efficiency of your furnace. If you have a really old furnace don't underestimate the benefit you will get from a modern fan motor for your air handler.

 

[arnolddeleon]

So quick and rough calculations:

110 Therms of gas, assuming that all used for space heating
Let's assume you have an 80% efficient furnace so that is 88 therms of actual heat.

Convert that to kWh using an online calculator spits out 2579 kWh of heat. If you were using a resistance heater that's what you need. With a heat pump you can probably safely assume a COP of at least 2 (more likely above 3) so that will between 860 kWh and 1300 kWh (if we assume the range is 2 to 3).

That's all very rough and I likely made a mistake but the sure-fire way to find out is post on the Internet.

 

[CWhite]

So quick and rough calculations:

110 Therms of gas, assuming that all used for space heating
Let's assume you have an 80% efficient furnace so that is 88 therms of actual heat.

Convert that to kWh using an online calculator spits out 2579 kWh of heat. If you were using a resistance heater that's what you need. With a heat pump you can probably safely assume a COP of at least 2 (more likely above 3) so that will between 860 kWh and 1300 kWh (if we assume the range is 2 to 3).

That's all very rough and I likely made a mistake but the sure-fire way to find out is post on the Internet.

Isn’t 2579 kWh’s the same as 2.56 megawatts? My heatpump normally draws about 3kw which equals 3 kWh if it ran for an hour straight. Are you sure there wasn’t a decimal place in there? 2.5 kWh sounds more like it.

 

[nwdiver]

Isn’t 2579 kWh’s the same as 2.56 megawatts? My heatpump normally draws about 3kw which equals 3 kWh if it ran for an hour straight. Are you sure there wasn’t a decimal place in there? 2.5 kWh sounds more like it.

That's for an entire month. 110 therms, 2579kWh or 2.579MWh for an entire month.

 

[CWhite]

Opps, apologies. Did not catch the 110 therms, which would be pretty spectacular to burn in one day. The most I have used in a month with the heat pump is 1,500 kWh’s. Before the heat pump the most gas I burned in a month was about 140 therms.

 

[arnolddeleon]

Another data point, it looks like I used around 720 kWh for the compressor on our heat pump. That does NOT include the energy for running the air handler. I don't have dedicated meter on that (yet). I keep the thermostat between 66 and 70. I'm sure that we ever actually reach 66. I have it set for smart recovery so it is already heating to come up to the wake temp in the early morning hours. 68-70 is quite comfortable if the objects in the house are not cold.