Switching a home between heating and cooling seasons

Changing a home from cooling mode to heating mode, or back again, is mostly a matter of getting the equipment that is about to run ready and switching off the parts that belong to the other season. A planned changeover avoids two common surprises: a furnace that has never had its filter changed turning on for the first cold morning, or an air conditioner that cannot breathe because leaves have packed around its outdoor unit.

The work runs in a sensible order. Start with the system that is about to take over, then clean and clear the equipment outside, then set the thermostat and confirm that the air coming from the vents is the right temperature. Finish with the smaller pieces that belong to one season or the other, such as window units, ceiling fan direction and a whole-house humidifier. Most of it can be done in an afternoon.

Check the system that is about to run

Before the first heating run of the season, replace or inspect the air filter and look at the furnace or heat pump for anything that seems out of place. A furnace that has sat idle for months may give off a dusty smell during its first few runs as settled dust burns off, and that is normal. A smell that is sharp, lingers or resembles scorched plastic is different. Switch the system off at the thermostat and have a qualified technician look at it. Any smell of gas, or a hissing sound near a gas appliance, means leaving the building and calling the gas utility or emergency services from outside.

Test each carbon monoxide and smoke alarm before the first heating run, and replace batteries or any unit past its manufacturer's service life. A gas or oil furnace or boiler should also get a yearly professional inspection and cleaning, so schedule that visit before the heating season rather than during the first cold snap.

Before the cooling season, book a service visit for a central air conditioner or heat pump if one has not happened in the past year. A technician can check the electrical connections, the refrigerant charge and the condensate drain. The drain matters because a clogged line can back up and leak water near the indoor unit, and a blockage is a quick fix when it is caught early.

Clean and clear the outdoor unit

The outdoor unit of a central air conditioner or heat pump moves a large volume of air, so leaves, grass clippings, seed pods and dirt can restrict it quickly. Before switching to cooling, look for debris packed between the fins and around the base. Keep a clear space of at least two feet on the sides and more above the unit, following the manufacturer's manual, and do not stack boxes, firewood or bicycles against it.

Before any water is used, turn off the outdoor disconnect switch or the breaker that serves the unit, and turn it back on only when you are finished. Then clean the fins with a garden hose at a gentle pressure, spraying from the inside of the unit outward where you can reach. Do not use a pressure washer, which can bend the fins. Bent fins are best straightened by a technician during the service visit.

A heat pump needs the same clearance in winter because it works in heating mode by pulling heat out of outdoor air. Clear snow away from the sides and top after a storm, and watch for ice building up on the coil. A short defrost cycle, when the unit briefly reverses to melt frost, is normal. Ice that keeps building up despite that is a sign that a technician should check the system.

Set the thermostat and confirm the airflow

Change the thermostat's mode only after the system has been checked. Choose heat or cool, then give the system a few minutes to start. Hold a hand near a supply vent in the room farthest from the thermostat. When cooling, the air should feel clearly cool. When heating with a furnace, it should feel clearly warm within several minutes. A heat pump in heating mode is different: its supply air normally feels only mildly warm, cooler than furnace air. Judge a heat pump by whether rooms reach and hold the set temperature, and call a technician if they do not. If a furnace gives only lukewarm air, or either system switches on and off in short bursts, note that and ask a technician to look at it instead of adjusting settings to compensate.

Then update the programmable schedule. A programmable or smart thermostat keeps the program from the last season, so check the wake and return times and the target for each period against how the household uses the home now. Clear any temporary hold left over from the summer, since it can keep the system working toward a target that no longer fits.

Handle the seasonal extras

Ceiling fans need their direction changed as well. In cooling season, run the fan counterclockwise when viewed from below, so the air pushes down in a steady breeze. In heating season, reverse it to run clockwise at a low speed. That draws cool air up along the ceiling and pushes warm air that has risen back down toward the floor. Switch the fan off before you change its direction, and wipe the blades, because dust on them spreads through the room when the fan runs.

Window air conditioners need attention when the cooling season ends. Remove the unit if you can and store it somewhere dry, or at least cover it with a cover made for that purpose, which keeps out rain, snow and insects. An uncovered unit left in an open window lets cold air in and warm air out all winter. Then check the weatherstripping around the window or the panel that fills the opening.

Keep the vents clear too. Furniture, curtains and rugs placed over a register block airflow in either season. Check that supply and return grilles are open and clean.

A whole-house humidifier on the furnace or air handler needs its own changeover step. Many households run one only in winter, so turn it off at the start of cooling season, closing its water supply if the manual calls for that. When heating season returns, restart it and replace the pad or water panel at the interval in the manual, which is often once each heating season.

Keep a short note of the date of each changeover, the filter you installed and anything you cleaned or repaired. The next changeover goes faster when you can see what was done last time, and if a problem appears in the first week of a new season, a technician will find it easier to diagnose when you can say when it started.