Best heat pump thermostat settings for winter, and what to avoid

If you switched from a gas furnace to a heat pump, your old habit of turning the heat way down at night and cranking it up in the morning may now be costing you money. Heat pumps work differently, and the settings that saved energy with a furnace do not always carry over.

Why the old advice changes. With a furnace or electric baseboard heat, the Department of Energy says you can save as much as 10 percent a year on heating and cooling by turning the thermostat back 7 to 10 degrees for 8 hours a day. For heat pumps, the same DOE page says programmable thermostats are generally not recommended, because setting a heat pump back in heating mode can make it run inefficiently and cancel out the savings.

Settings that work well. The Northeast Energy Efficiency Partnerships (NEEP) consumer guide gives practical advice that applies in California too:

Step 1: Choose a comfortable temperature and leave it there. NEEP advises avoiding frequent adjustments and keeping indoor settings steady. Heat pumps are designed to run for long stretches at low speed, which is their most efficient way to operate.

Step 2: Use Heat mode, not Auto. NEEP recommends picking Heat or Cool on the thermostat or remote rather than Auto, so the system does not flip between heating and cooling on mild days.

Step 3: Leave the indoor fan on Auto most of the time so it runs as needed, and keep the vanes on ductless units open.

Step 4: Do not shut it off on cold nights. NEEP says turning it up a bit is better than turning it off, and to avoid cycling it on and off to control temperature.

Step 5: If you kept your old furnace as backup, set that thermostat 5 to 10 degrees lower than usual so the heat pump does most of the work, and use the backup only when needed.

Small maintenance with a big payoff. NEEP suggests cleaning or replacing indoor filters every 2 to 6 weeks, keeping the outdoor unit clear of debris, and never covering it. The DOE notes that dirty filters and coils restrict airflow, and that strong wind on the outdoor unit can cause defrost problems.

The noise that worries people. On cold, damp mornings the outdoor unit may pause, make a whooshing sound or release a little steam. That is usually the defrost cycle, when the system briefly reverses to melt frost off the outdoor coil. NEEP also lists gurgling or swishing from indoor ductless units during defrost as normal. If you see error lights or the house is not warming, check the owner's manual and call your installer.

A next step for today: check your thermostat's mode and schedule. If it is set to Auto or has a deep overnight setback, try a steady Heat setting for a week and compare your daily usage in your utility account.