Thread by @DanEspo14

A month ago, I shared how my electric heat pump kept my house warm during temps as low as -15°F, dispelling myths that newer models can't manage the cold. With my utility bill in hand, I now have more good news: I likely saved ~$100 vs. a gas furnace! 1/

https://twitter.com/DanEspo14/status/1606005868079636480?s=20&t=ZlDHHpJpLGaV5jD5ANom6Q

What does "likely" mean here? Well, you can't easily compare bills year-over-year to estimate the impact of moving from a gas furnace to an electric heat pump. You need a counterfactual--what would my bill have been last month (Dec-Jan) if I still had my gas furnace? 2/

For example, if gas and electricity prices rose significantly from the prior year, even energy-saving actions could appear to be more expensive when directly comparing bills. But using a counterfactual can reveal what you would have paid if you took no action. 3/

Ostensibly, I paid $51 more this cycle than last year. But after estimating an appropriate counterfactual, I look to have saved $104! I'll walk through it all & encourage anyone to interject if they think I made any *material* errors (noting some simplification is necessary). 4/

There are 4 major factors I considered: 1) diffs in gas and electricity prices; 2) diffs in number of days included in my billing cycles; 3) diffs in average temperatures; and 4) a very clear, explainable outlier in this year's electricity use. I'll address these in turn. 5/

1) While my average $/kWh elec rate barely changed year-over-year (+7%), my average $/therm gas rate skyrocketed (+57%). Applying this year's rates (plus fixed fees & tax rates) to last year's usage (when I had a gas furnace) moves me from a $51 loss to $25 savings! 6/

But, also this year, my gas cycle included one more day than last year; my elec cycle included two more days than last year (both days w/ on-peak pricing); temps were 4-5°F colder; and I had an 11-day period marked by an usual electricity-using event (more on that later). 7/

2) To account for this year's extra billing cycle days, I calculated average gas and elec usages per day from last year and applied those factors to the number of days in this year's cycles. This drives an extra $14 in savings relative to if I still had and used a gas furnace. 8/

3) To account for this year being 4-5°F colder (for gas and elec cycles--which don't line up--respectively), I decided to use usage data from Feb-Mar 2022 (when I still had a furnace and average temps were equal to this cycle at 32°F) instead of Dec '21 - Jan '22. 9/

Again, I applied that gas and elec usage data (adjusted for differences in the number of days in the billing cycles) to the price structures for Dec '22 - Jan '23. This led to an extra $35 in savings, now at a total of $74 relative to owning a gas furnace. 10/

4) So, what was this big outlier event? Unfortunately, a burst pipe flooded my crawl space on Christmas morning. (The space was warm + water dripped from faucets, but a pipe feeding an isolated hose bib wasn't properly winterized despite us paying for that work...) 11/

From this daily electric usage data, the rightmost red circle shows the days when we were running pumps (removing >1,500 gallons), fans, and dehumidifiers around the clock--something we obviously don't do every year. (Leftmost circle shows elec usage during the cold snap.) 12/

Here's the graph again with temperature data. By pulling this data to Excel, I was able to estimate the impact of the water removal + drying processes and add it to the counterfactual--about $30. I was careful to account for temperature and peak/off-peak pricing differences. 13/

In sum: when you put it all together, I likely *saved* over $100 this billing cycle with my electric heat pump vs. if I still had a gas furnace! Sure, I paid 2x my daily average on Dec 22 and 23 vs the rest of the cycle to heat my home, but that impact was dwarfed by savings. 14/

So, today's heat pumps can keep your house just as warm in sub-zero temps as a gas furnace (and cool during the summer!), do so at lower operating costs, and cut GHG emissions. Better yet, #InflationReductionAct funds, can help you install your own! 15/

rewiringamerica.org/circuit-breake…

Now, what Qs do you have about heat pumps, my experience, or my calcs? Did my best w/ the data I had, but am I missing anything? Let me know--we're all learning together en route to a climate-safe future (while improving our quality of life across all other facets as well)! 16/16

FYI, some real-world/Denver-based heat pump operating cost analysis in this thread if interested. @DenverCASR @rewiringamerica @samcalisch @RMIBuildings @ChazTeplin @ACEEEdc @drvolts @carbonswitch @curious_founder @meganschrader @CorbinHiar @Shemkus @elephant_energy