![]() Our Heat Pumps Have Been Very Good This Year All over California, I hear skepticism about switching from gas to heat pumps.
So, I decided to do it myself. 2024 was the first full year when our 3-bedroom 2,000 square foot home in Long Beach was All-Electric. Let’s see what our utility usage says about electrification. ![]() While on gas, our house used 5,750 kWh of electricity and 250 therms of gas with the most efficient gas systems money could buy: a 95% efficient tankless gas water heater and a 95% efficient 2-stage gas furnace. As an energy consultant, I knew that heat pumps were more efficient than gas appliances, with COPs above 3.0 (300% efficiency). My energy modeling software predicted the energy use for heat pumps in my climate zone, but you never really know until you try it and measure the results. With heat pumps replacing the last two gas appliances in my home, we used 6,415 kWh of electricity and no gas in 2024. That’s an increase of only 685 kWh (about 12%). We even had the utility come and remove the gas meter completely, which eliminated our gas bill. How could we switch all of our space and water heating from gas to electricity and see such a small increase in electricity usage? ![]() Heat Pumps Really Are That Efficient
With gas, I wasn’t able to determine the exact usage attributable to space heating versus water heating. Assuming that my hot water usage stayed relatively constant each month, looking at my summer gas usage gave me a good estimate of my monthly water heating usage, with the increase in monthly gas use during the winter attributable to space heating. So I estimated my gas usage to be 50 therms for water heating and 200 therms for space heating per year. In 2023, we installed a Rheem 50-gallon heat pump water heater to replace the tankless gas water heater. It’s installed in a well-ventilated closet on the side yard, so it pulls heat from the outside air. We chose a 120-volt unit, since there was already a 120-volt outlet in place from the gas tankless system. Note that most HPWH units installed in California are the 240-volt variety that come with backup electric resistance elements for really cold days or when the heat pump can’t keep up with the hot water demand. Installing a 240-volt unit would have required bringing out an electrician to run a new circuit. We calculated that 50 gallons would be enough hot water to supply up to 4 consecutive showers, since we have efficient shower heads (1.8 gallons per minute) and our climate never falls below the heat pump cutoff temperature (about 38 degrees). That has proven true. The data from my home energy monitoring system shows that in 2024, our family used 432 kWh to heat water, averaging 1.2 kWh per day or 36 kWh per month. Assuming an average electric rate of $0.35/kWh, I estimate we are paying ~$12 a month to run the heat pump water heater. In comparison, the 4-5 therms of gas we used with the tankless water heater cost us ~$10 per month (at ~$2.00-$2.50/therm), so let’s call water usage a push on utility costs. Plus, I can’t tell you the satisfaction taking a shower with hot water you know was produced without burning gas – a cleaner feeling all around! By scheduling the heat pump to avoid peak hours (4-9 pm) and using hot water during the day when solar panels are active, your showers can feel even cleaner. “Heat pump water heaters don’t have the same capacity as gas models”, true or false? Answer: False-ish. A 50-gallon tank water heater has the same capacity, whether it’s heat pump, electric, or gas. But the statement is true if we’re talking about “heat rate” – the speed at which the water heater can replenish hot water as it’s used. We’ve never run out of hot water, though for most of the year, it’s just my wife and I using it. The holidays gave us a chance to put the water heater to the test. The chart below shows daily electricity usage on our water heating circuit in December, 2024. Note that there are some other receptacles drawing power on this circuit, but it’s mostly water heating. The beginning of the month shows usage with just my wife and me at home, down around 1 kWh per day. Then our two daughters came home and we were making hot water for 4-6 showers a day instead of two, so our water heating usage went up to 3 kWh per day some days. That’s the holidays for you. I made it a point to shower last on the day when we needed six showers and that was the first time I noticed our hot water had cooled a bit. It was still a good hot shower, but our 50 gallon tank ran low at that point. That made me feel more confident recommending heat pump water heaters to my clients. Install a 240V model with back-up resistance elements and you’ll be better off than we are with our 120V unit with no back-up. ![]() 2. Space Heating My energy modeling runs over the years had shown there to be significant energy and utility bill savings possible by switching from gas furnaces to minisplit heat pumps. But the modeling world and the real world are two different things. Would my utility bills go up heating our home with an electric heat pump? Do they even work, as the skeptics have been asking? There was only one way to find out… We had a ducted gas furnace in the attic and an air conditioner, often called a split system because the furnace was used for heating and the air conditioner for cooling. The simplest change-out for a ducted split system like this is to replace the furnace and air handler with a heat pump, keeping the existing ductwork, supply, and return registers. We installed a Mitsubishi “multi-position air handler” with similar dimensions to the old unit. This connected to a new outdoor unit (see earlier photo captioned “My Heat Pumps Have Been Very Good This Year”) with refrigerant lines. The 240-volt, 30 amp circuit that served the old air conditioner now serves both the new indoor and outdoor units, freeing up the 120-volt circuit previously used by the old air handler in the attic, reducing panel space usage. The old system used energy in three different ways: gas for the furnace, electricity for the air conditioner, and electricity for the air handler. My energy monitoring system counted 1,434 kWh and our gas bill showed 200 therms to run all three pieces of the HVAC system. The air conditioner was about 1,000 kWh in summer and the air handler was about 430 kWh running all year for heating and cooling. The heat pump uses a single circuit, but how much higher would its energy use be handling heating and cooling year-round, compared to the 1,434 kWh with the old system not providing heating — Double? Triple? Based on my energy models, I knewthat heating use in Long Beach is higher than people think, but I expected HVAC electricity use to double, even with the efficient variable capacity inverter driven heat pump we installed. These are able to purr along at low-load throughout much of the year, which is a big part of where they get their high efficiency from. The answer at the end of the year shocked me – the electricity usage for HVAC went up only 31%, and the old system was efficient, how was this possible? Was the weather different in 2024 from the year I collected the data on the old gas furnace split system? Some digging was in order… 3. The Digging Confirms that Minisplits are Very Efficient Question #1: “Was the weather different and does that explain why electricity usage only went up 31% with the heat pump?” Answer: Nope. Daily average temperatures are shown in the chart below; they were very similar for the two data collection periods. The mean was 1.2 degrees cooler in 2023 with the gas furnace. Measured in total heating and cooling degree-days, 2023 was 2,525 and 2024 was 2,252. The weather certainly doesn’t explain why the heat pump was able to do the same job as the old gas system without using much more electricity. As a side note, we also installed a ductless minisplit heat pump system in our all-electric ADU, which we completed in 2023. It used only 544 kWh to heat and cool the ADU last year, which is 576 square foot and 1 bedroom. So both our heat pumps have been very good this year. Question #2: “Was the heat pump’s higher efficiency the reason? Was it more efficient at heating or cooling?” Answer: Yes, YES, and Yes. To evaluate this, we looked at cooling energy use per cooling degree-day. This accounts for weather variations and allows us to measure efficiency across different conditions. Heat pump cooling electricity usage per cooling degree-day: 1.00 Old air conditioner cooling electricity usage per cooling degree-day: 1.47 The old air conditioner had two stages, one for mild days and the second one kicked in when needed for hotter days. It had a 16 SEER rating, better than code minimum. However I was shocked to learn it used 47% more electricity to cool our house than the heat pump! In fact, 2024 had 20% more cooling degree-days than 2023, meaning that equivalent weather years would have shown the heat pump outperforming the air conditioner by well over 50%, maybe even 60%. Heating is tougher to compare since the furnace used gas and the heat pump uses electricity. However. analysis of the old system shows it used 200 therms of gas plus 242 kWh of electricity for air movement during the heating season. If we convert the 200 therms to theoretical kWh using a factor of 29.3 kWh per therm, we can compare the heating energy use of both systems. The new heat pump used only 911 kWh of electricity in heating season. Heat pump heating electricity usage per heating degree-day: 0.71 Old furnace heating energy usage per heating degree-day: 3.57 This comparison highlights the heat pump’s efficiency and the real-world meaning of its 300% efficiency. The furnace was using 5X more energy to heat our house than the heat pump! Perhaps that 300% efficiency figure was an underestimate. The year we measured the gas furnace had 34% more heating degree-days than the year with the heat pump. But we’ve accounted for that in the metrics above. Perhaps our heat pump would have used ~1,200 kWh in heating mode if it were to go through another year like 2023. Even so, we would still be very satisfied with that, especially compared to the old gas system. ![]() 4. What About Cooking and Laundry? Cooking electricity usage, 2024: 436 kWh Washer & Dryer electricity usage, 2024: 550 kWh We have a 4-circle (can’t call them burners) induction cooktop and electric oven for cooking. We cook most nights, using ~500 kWh per year. In late 2023, we added a countertop air fryer, which we use occasionally instead of the oven or cooktop, reducing our 2024 cooking usage by ~125 kWh. At an average cost of $0.40/kWh, 500 kWh costs about $200 per year for cooking electricity usage, not bad. Note that I used a higher per-kWh rate for cooking, as it’s typically done in the evening when electricity rates are highest and our solar panels are no longer producing. We have a stacked Miele washer and heat pump clothes dryer for laundry. They used about the same amount of electricity as our cooking: 484 kWh in 2023 and 550 kWh in 2024. When we had a gas dryer, electricity usage was 258 kWh, so the heat pump dryer added about 230 kWh per year. For an electric resistance dryer, it would have been 3X that amount. The difference in utility costs for laundry is that we can run it during the day on solar power from our roof. I bet that half of our laundry usage costs us nothing, thanks to solar power. 5. Actual Utility Bills You won’t believe this, but our utility bills were much lower all-electric. I’ll bottom-line it for you. 2024 utility bills (all-electric): $1,400*** 2023 utility bills (mixed fuel): $763 electric + $637 gas = $1,400 *** EV charging usage was 1,055 kWh higher in 2024 than 2023 If you exclude the extra ~1,000 kWh used to “fuel” our EVs, our 2024 all-electric utility bills were much lower than our utility bills with gas, probably about $400 lower per year! I say “probably about $400 lower” because calculating utility bills in California is really complicated these days. There are multiple layers of complexity:
We paid $1,400 in electricity bills this year, with our home converted to all-electric and a 4.4 kW solar system (now 9 years old) on the roof. For the first 4 years our total annual electric bill was $0, but since then we’ve added two electric vehicles which we charge at home, and we’ve faced rate increases in California. In addition to our home’s operating costs, the $1400 annual electricity bill also covered almost all of our transportation costs. We used 2,800 kWh of electricity to “fuel” our two EVs – a 2019 Chevy Bolt and a 2023 Kia Niro. That’s 11,200 miles worth of travel at 4 miles per kWh, covered by our $1,400 electric bill. We also charged occasionally at public stations during road trips, and probably drove 15,000 miles in total this year. To have a single bill cover the cost of operating your house and your cars is really convenient. I estimate we would have spent about $1,500 on gas for 11,200 miles of travel this year (30 mpg @ $4.00 per gallon), so our utility bills of $1,400 mostly covers transportation. Our house operates for next to nothing, thanks to efficient heat pumps, solar panels, and good building envelope. And we no longer have the gas bill coming to our email inbox, which cost us $637 in 2023, the last year we used gas. 6. Key Takeaways My family is very satisfied with our switch from gas to electric. The house operates trouble-free and keeps us comfortable. Here’s the executive summary of results:
![]() APPENDIX: For Energy Modeling Enthusiasts My business is energy modeling. We use computer models of buildings to optimize their energy efficiency and verify compliance with the California Energy Code, also known as Title 24. But we rarely get to compare actual energy usage to modeled. I modeled my actual house with every feature from insulation to windows and I modeled it before we electrified and after. Here's what I found. The modeling software (Energy Pro v9 for 2022 energy code compliance) overestimated energy use in the mixed fuel home by 18% on electricity and 26% on gas. The overestimate was much larger in the all-electric home: the modeling software estimated energy use would be 50% higher than it actually was! The table below shows the actual usage versus the modeled usage by end use. The biggest over-estimates by the model were in the all-electric heating (+163%), water heating (+102%), and cooling (+49%). In the mixed fuel model, the software also over-estimated water heating gas usage (+112%), but other estimates were much closer. Judging by our family’s actual usage, the modeling software gives over-estimates of energy use and larger over-estimates for all-electric homes. This suggests that the savings for electrification are larger than the software predicts, which makes electrification a more attractive proposition than we had assumed based on the software’s predictions. This is one home with one family and should not be assumed to be consistent across California, but it is one useful data point to try to understand electrification's benefits.
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AuthorsNick Brown, CEA Archives
January 2025
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