How to Get Your HVAC Ready for a Texas Winter

In The Woodlands, the transition from cooling season to heating season happens fast. One week you are running the AC at 73, and the next you wake up to 38 degrees and switch to heat for the first time since March. That first call for heat is when most heating failures show up, because the system has been sitting idle for six or seven months and nobody checked it before flipping the switch.

Run the Heat Before You Need It

The single most useful thing you can do is turn the thermostat to HEAT on a mild day in October or November when it is 55 or 60 outside, set it to 72, and let it run for 20 minutes. You will probably smell a burning dust smell for the first few minutes. That is normal. Dust settles on the heat exchanger and the electric elements during the off season, and it burns off on first use. If the smell does not clear within ten minutes, or if it smells like rotten eggs (natural gas) or hot plastic (electrical insulation), shut the system off and call for service.

Running it on a mild day gives you time. If something is wrong, you find out when the outside temperature is 58, not 28. You can open windows. You are not in a crisis. A heating failure discovered in December when the forecast says 19 degrees puts you in line behind every other homeowner who also did not check.

Replace the Filter

If you have been running the AC all summer, the filter has five or six months of dust on it. A restricted filter on a gas furnace does the same thing it does on the AC side: it starves the system of airflow. But on a furnace, restricted airflow causes the heat exchanger to overheat, which trips the high-limit switch and shuts the burners off. The blower keeps running, blowing cold air. The homeowner thinks the furnace is broken. The furnace is protecting itself from a cracked heat exchanger, which is a $1,500 to $3,000 repair or a full replacement. The filter was $12.

Check the Flue and Combustion Air

Gas furnaces need two things from the outside world: combustion air to burn the fuel and a flue path to exhaust the combustion gases. High-efficiency furnaces (90% AFUE and above) use PVC flue pipes that exit through a side wall. Standard-efficiency furnaces (80% AFUE) vent through a metal flue pipe into a chimney or directly through the roof. In both cases, check that nothing is blocking the exhaust. Wasp nests in PVC terminations are common in Texas. Bird nests in metal flues happen regularly. A blocked flue is a carbon monoxide hazard, full stop.

Combustion air intakes deserve the same check. If the furnace is in a closet, that closet needs either louvered doors or dedicated combustion air ducts. Do not store boxes, cleaning supplies, or anything flammable in a furnace closet. This is not fussiness. It is fire code, and it exists because a furnace in a sealed closet will backdraft combustion gases into the living space when it runs out of air to burn.

Heat Pumps: A Different Checklist

If your home has a heat pump instead of a gas furnace, the outdoor unit runs year-round. In cooling mode it rejects heat outside. In heating mode it absorbs heat from the outdoor air and moves it inside. When outdoor temperatures drop below about 35 degrees, the coil frosts over and the unit goes into a defrost cycle, reversing briefly to melt the ice. This is normal. Steam or water dripping off the outdoor unit during defrost is not a problem.

• Clear leaves and debris from around the outdoor unit before heating season starts
• Make sure the defrost drain is clear so meltwater does not pool and refreeze at the base of the unit
• Check that the auxiliary heat strips are working. Set the thermostat to EMERGENCY HEAT for a few minutes and verify warm air at the registers. Switch it back to normal HEAT when done.
• If the unit runs in heat mode but the air at the registers is barely warm, the refrigerant charge may be low. Heat pumps lose heating capacity faster than cooling capacity when low on charge.
• A heat pump that never defrosts in cold weather has a failed defrost board or sensor. It will ice over completely and stop heating.

The Thermostat

If you have a programmable or smart thermostat, update the schedule for heating season. A schedule that made sense for cooling (pre-cool the house before you get home) does not apply in reverse. Most programmable thermostats have separate cooling and heating programs. Set the heating program to drop to 65 or 66 at night and recover to 70 in the morning, but give it lead time. A gas furnace heats fast. A heat pump heats slowly. If you set recovery for 6:00 AM with a heat pump, start the recovery at 5:00 AM.

Carbon Monoxide Detectors

If you have gas appliances (furnace, water heater, range, dryer), you should have at least one carbon monoxide detector on each level of the home and one within 15 feet of each sleeping area. CO detectors have a limited lifespan, typically five to seven years. Check the manufacture date on the back. If it is past its rated life, replace it before heating season. A CO detector is not optional equipment in a home with gas combustion appliances. It is the last line of defense against a cracked heat exchanger or a blocked flue that you did not catch.

AOT Mechanical handles heating repair and replacement for residential, commercial, and mobile home customers across The Woodlands. They have been at it since 2009, and they offer consumer and commercial financing for equipment replacements. Get the system checked before the first cold front. Call (281) 883-9972.