Five Winter Energy Myths That Cost Arizona Homeowners Money
Advice written for cold climates does not transfer cleanly to a Valley winter, and some of it actively backfires here.
Common winter energy advice — deep thermostat setbacks, closing vents in unused rooms, covering the outdoor unit, cranking the thermostat for faster heating, and space heaters saving money — either does not apply in Phoenix or causes problems. Heat pump homes in particular need different strategies than the standard cold-climate advice assumes.
Myth one: always set back deeply at night
True for a gas furnace. Actively counterproductive for a heat pump.
A furnace produces heat at the same cost per unit regardless of how far the house has drifted, so recovering ten degrees simply takes longer. The setback genuinely saves.
A heat pump is different. When the thermostat sees a large gap between current temperature and setpoint, it engages auxiliary electric strip heat to recover faster — and strip heat costs roughly three times as much. The deep setback saves for eight hours and hands it all back in a forty-minute recovery.
With a heat pump, keep setbacks to two or three degrees.
Myth two: close vents in rooms you do not use
This is the most persistent HVAC myth there is, and it makes things worse in both seasons.
Your duct system was designed to deliver a specific total airflow. Closing registers does not reduce what the blower produces; it forces the same air through less duct, which raises static pressure.
On a furnace, that restricted airflow lets the heat exchanger overheat and trip the high-limit switch, which is one of the most common causes of winter short cycling. In cooling season the same restriction freezes the evaporator coil.
It also increases duct leakage, because higher pressure pushes more air out through every gap — in a Phoenix attic, straight into a space you are not trying to condition.
Keep at least 80 percent of registers fully open.
Myth three: cover the outdoor unit for winter
If you have a heat pump, this is genuinely harmful — the outdoor unit runs all winter and needs airflow. Covering it prevents it from working and can damage it.
Even on a cooling-only air conditioner, a full wrap-around cover traps moisture against the coil and creates an attractive nesting environment for rodents, which chew wiring. A top-only cover that keeps debris out while leaving the sides open is acceptable; a full cover is not.
In Phoenix specifically, there is very little reason to cover an outdoor unit at all. We do not have the snow load or the freeze-thaw cycling that motivates the practice elsewhere.
Myth four: cranking the thermostat heats the house faster
It does not. A furnace has one output, and a heat pump has at most a few stages. Setting the thermostat to 80 when you want 70 does not increase output; it just means the system runs past 70 and overshoots.
On a heat pump it is actively expensive, because the large gap triggers auxiliary strip heat that would not otherwise have run.
Set it where you want it and let it get there.
Myth five: space heaters save money
Sometimes, narrowly. A space heater in one room while the central system is set back can save money if you are genuinely occupying only that room for an extended period.
What does not save money is running several space heaters throughout the house. Electric resistance heat is the most expensive way to produce heat, and multiple units running simultaneously will cost more than the central system would have.
There is also a safety dimension. Space heaters are a leading cause of residential fires. If you use one, it needs tip-over protection, its own outlet rather than a power strip, clearance from anything flammable, and it should never run unattended or overnight.
What actually works in a Valley winter
- Set the auxiliary heat lockout on a heat pump — the single highest-value change
- Change the filter; a restricted filter makes a furnace trip on high limit
- Seal and insulate attic ductwork — it loses heat in winter exactly as it loses cooling in summer
- Open blinds on south-facing windows during the day for solar gain, close them at night
- Use ceiling fans in reverse at low speed to circulate warm air off high ceilings
- Keep the thermostat steady rather than chasing it
- Verify the heat pump is actually running rather than relying on strip heat
Frequently asked
Should I close vents in rooms I do not use?
No. Closing registers raises static pressure across the system, which reduces total airflow, can trip a furnace high-limit switch, freezes evaporator coils in cooling season, and increases duct leakage. Keep at least 80 percent of registers fully open.
Does turning the thermostat up higher heat the house faster?
No. Heating equipment has a fixed output, so a higher setpoint just means the system runs past your target and overshoots. On a heat pump it is actively expensive, because the large gap triggers auxiliary strip heat.
Should I cover my outdoor unit in winter in Phoenix?
No, especially not a heat pump, which runs all winter and needs airflow. Even on a cooling-only unit, a full cover traps moisture and attracts rodents that chew wiring. Phoenix has none of the conditions that motivate covering units elsewhere.