Holding one temperature all day isn't cheaper — but if you have a heat pump, there's a catch almost no one tells you about.
Published by Fairfax Mechanical · fairfaxmechanical.co · August 2026
Should you leave the thermostat at one steady temperature, or turn it back when you're at work and asleep? Plenty of people insist holding constant is cheaper — that making the system "work harder to catch up" costs more than you saved. For most homes, that's simply not true. But there's a genuine heat-pump exception that generic advice never mentions, and getting it wrong can quietly inflate your bill.
Why Setbacks Save (The Myth, Debunked)
A house loses heat in winter (or gains it in summer) in proportion to the temperature difference between inside and outside. Set the thermostat back — let it drift to 62° while you're at work instead of holding 70° — and you shrink that gap for those hours, so the home loses less heat and the system runs less.
The energy to reheat when you return is always less than what you saved, because you avoided hours of fighting a bigger gap. That's why "it costs more to recover than you saved" is a myth: recovery is real, but it never outweighs the savings.
How Much, and How Big a Setback?
The U.S. Department of Energy's rule of thumb: ~1% savings per degree of setback, sustained over about 8 hours. A practical target for a standard furnace or AC is 7–10°F for 8+ hours while away or asleep. Bigger and longer setbacks save more — so the wins come from long daily stretches, not small frequent tweaks.
Winter: set it DOWN while away/asleep
Summer: set it UP while away — same physics, reversed
The Heat Pump Exception (Read Before Deep Setbacks)
Here's the caveat almost nobody mentions. A heat pump heats efficiently by moving heat — but within a range. Set it back deeply, then ask it to recover several degrees fast, and the thermostat often kicks on auxiliary heat: electric resistance strips that cost far more than the heat pump itself. That pricey backup can cancel — or exceed — your setback savings.
The physics still favors saving; the problem is how a heat pump recovers. Fixes:
Use smaller setbacks (a few degrees, not a deep drop)
Avoid demanding rapid recovery
Best: a heat-pump-aware thermostat with "adaptive recovery" that climbs back gradually on the heat pump alone, no aux heat
Let a Smart Thermostat Do It
A programmable/smart thermostat schedules setbacks automatically and — on good models — uses adaptive recovery to dodge the aux-heat trap. Many qualify for a Dominion Energy rebate.
Not sure how to set back a heat pump without triggering expensive backup heat? Fairfax Mechanical helps you choose and configure the right thermostat across Northern Virginia. Schedule at fairfaxmechanical.co/contact.
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