A decade old argument in our house relates to the right indoor temperature for our long, chilly, and wet Portland winters. It’s not just a matter of what temperature makes each of us most comfortable (a common household debate) but in our house, where energy savings reign king, it’s also a matter of what temperature is most efficient when it comes to carbon reductions. For years, Joe (husband and co-author of Decarbonize Your Life) has tried to covertly lower the temperature to save money and energy while Naomi (wife and co-author) not-so-covertly tried to increase it because, as our daughter often exclaims, “Mama’s fingers are like ice cubes!”
We’ve been proud ductless heat pump users for over ten years but only recently learned how they work best. Let us share our lessons so that you, too, can resolve household arguments and start enjoying the blissful comfort of consistent temperatures, energy savings, and no stress thermostat control. The takeaway: heat pumps work best when left at a consistent temperature. In other words, they are happiest, most efficient, and save more money when you set a comfortable temperature and don’t change it during the seasons when you use them.
Our humble living room heat pump head has been keeping our home warm and cool for over a decade.
How We Used to Control Our Heat Pumps
We could regale you with stories from our 15 years together when Joe went to herculean efforts to save energy. Here’s just one: for several months in 2011, he set his daily alarm to 4:30 am so he could turn on the water heater, which he had switched off the previous night, before our housemate got up to shower. (Joe doesn’t think it was that early or that much effort.) For the last decade in our current home, the first sound Naomi heard each morning was the beeps of Joe raising the temperature on the ductless heat pump remote, in our bedroom, so it was a balmy 64 when she got out of bed.
Then came 2021 and our first “aha” moment about our heat pumps. It came during Portland’s epic heat dome, when the city reached a record-breaking 114 degrees. We both have a high heat tolerance and think that AC is way overused in America. As proud AC nonconformists, we had only ever used the cooling function on our heat pumps a couple times and regularly maintained summer comfort with passive cooling and shading. (Portland’s cool summer nights mean that by opening windows in the evenings and closing up during daytime hours of peak heat, our house always stayed pretty comfortable.)
So when Portland’s temperatures creeped above 100 degrees multiple days in a row, and had a forecast of 115 Fahrenheit (46 Celsius), we figured it might be time to take advantage of the cooling cycle on our heat pumps. Once Joe finally gave the greenlight, around 2:00 pm, we closed the blinds and turned the heat pumps to cooling mode. We were excited to enjoy this AC amenity that’s still somewhat unusual in our part of the world. Three hours passed, and the continuously running heat pumps only lowered the temperature by a couple degrees. Naomi worried the cooling function was broken since we’d never really tested it. We continued to melt, and the house never cooled below 90, so we returned to our passive cooling techniques and switched off the heat pumps with forecasted temperature drops.
A few weeks later, trying to troubleshoot our “broken cooling function,” we learned from Joe’s contacts at the local Heat Pump Store that heat pumps don’t work the way we’d attempted to make them. They provide slow constant heat or cooling, and since we’d had our system off through that record setting stretch, it was a huge amount of work for them to lower from nearly 100 degrees during the hottest part of the day. These machines like to run marathons, not sprints.
“Awesome,” said Naomi, “now we can leave our house at a more comfortable temperature for more of the year.” “OK, that might be true when Portland exceeds 110,” insisted Joe, “but I still know better than the recognized Heat Pump experts and will continue to control the temperature based on what my gut tells me will make our house the most efficient ever.” (Joe doesn’t think he sounded this obnoxious.) Daily and hourly beeps on the heat pump remote continued as the soundtrack of our life.
How We Now Control Our Heat Pumps
Fast forward to fall 2022. Joe has worked closely with, and established a profound respect for, the great people at Efficiency Maine. In a webinar he hosted with them on cold climate heat pumps, he learned about research that made him see the error of his ways. Yes, this data convinced him Naomi’s approach to keeping a consistent temperature may have been right all along.
Long story short, by maintaining heat pumps at a constant operating temperature, they run more efficiently! Incredibly, and counterintuitively, heat pumps will save the most dollars, energy and carbon emissions when you don’t regularly change their temperature.
In the first case study below from the Department of Energy (see graphs below), heat pumps used significantly less energy when run at a constant temperature. Incidentally, the study looked at a home with first and second floor heat pumps (red bar in graph below), and the constant temperature essentially eliminated the need for the second floor system.
A bit more about how heat pumps work explains this phenomenon. Heat pumps provide a slow, steady heat, unlike the temperature blast most of us expect from a furnace. Heat pumps steadily draw temperatures from the surrounding air, little by little, to maintain a constant temperature. When turned off at night, energy usage drops, of course. But then the next morning, when the system kicks on, it has to work super hard to get back to comfort levels which you can see in the daily morning spike in the graph below (brown box). Nighttime (or any time) setbacks make heat pumps work hardest during the time of day when it’s most challenging for them to find heat in the air. The lesson for heat pumps: find a comfortable temperature and leave it there. If you want to reduce it a bit at night, you can drop a few degrees, but just don’t turn it way down or all the way off.
So this past fall, after some debate on the set points, we set the living room heat pump head to 66 degrees and the bedroom one to 63, and we stored the remote in the pantry. (Another perk is less clutter, as the remotes often floated around the house, became toys, or ran out of batteries.) We now get out of bed in the mornings and comfortably walk into the living room, which used to drop well below 60 at night when the heat was off. Even though our household set points are still relatively low, the constant nature of the heat means that the ambient temperature in our house always stays quite comfortable. Another big change is that we rarely turn on the backup electric heat in the rooms without heat pump heads because the warmer temperatures consistently permeate our home.
We now have several winter months of comparative data and found that we used 7% less energy this winter by leaving our heat pumps at a standard temperature, and this winter was colder! (4020 kWh in winter months of 2022–2023 compared to 4304 kWh in winter 2021–2022.)
Check out this Electrify Now presentation on Cold Climate Heat Pumps if you need further convincing (like Joe did) that the “set it and forget it” approach is best when it comes to carbon, energy and dollar savings. (Start at 48 minutes if you’re looking to understand more about improved performance with a steady set point.)
Our Wish for You
You may still argue with those in your home over the right set point for your heat pumps, but once you agree on a number, you can avoid daily (or hourly) arguments about adjustments. And based on our experience, this consistent temp, even if it’s on the low end of typical ranges, will bring a surprising level of comfort that makes your living space feel so much warmer and cozier than the major swings that come with the on-off operation of a gas fired heating system.
May your heat pumps bring you energy, carbon and dollar savings, household comfort, and marital bliss.
This article is part of a series called Decarbonize Your Life. With modest steps and a middle-class income, our family has dramatically reduced emissions and is sequestering what remains through a small reforestation project. Our life is better for it. If we can do it, you can too.
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