![Switched gas furnace → heat pump (July 2024): ~18% lower energy bill at the same outdoor temp [OC]](https://preview.redd.it/xzuydcboffbh1.png?auto=webp&s=3e50d0bfa4ee61ca8fa401a570b4135442e47bce)
Switched gas furnace → heat pump (July 2024): ~18% lower energy bill at the same outdoor temp [OC]
Converted our house from a gas furnace to a heat pump in July 2024 (Canada). We still have a gas stove, and we gained central AC for the first time as part of the install.
To compare apples-to-apples, I plotted total monthly energy cost (gas + electricity) against average daily outdoor temperature, and restricted both series to ≤10°C so the comparison stays within heating season for both — no AC cost muddying the "after" data.
Before (gas furnace): y = -8.08x + 230.16
After (heat pump): y = -5.60x + 188.54
At 0°C, that's $230/month before vs. $189/month after — about 18% lower, with the same gas stove cost baked into both, so the difference is attributable to the heating source itself.
The slopes are the other interesting bit: the heat pump line is noticeably flatter (-5.60 vs. -8.08), meaning our costs are less sensitive to how cold it gets outside. The gas furnace had to work (and cost) proportionally more as temps dropped; the heat pump's cost curve is comparatively steadier.
A few notes for the data purists:
- Data pulled directly from utility bills (Enbridge gas + electricity), anomalies normalized (estimated gas usage vs actual reading restatements), matched to average daily temp for each billing period.
- Restricted to ≤10°C specifically to exclude AC-driven costs, since AC is new post-heat-pump and would confound a straight before/after comparison at warmer temps.
- Sample size is modest (roughly 8-10 points per series), but each point represents a full billing cycle (~30 days) of actual metered usage, not a spot reading — so while there are few points, each one is already an aggregate/average over a month, not a noisy single-day sample.