The heat can safely come off in Virginia by mid-to-late May for most homes, and the air conditioner usually needs to run by June. But state weather data shows that gap is tighter than people expect: the mildest month on record here still carries real heating and cooling demand, so plenty of houses end up calling for both systems in the same week, once in spring and again in fall.
The quietest month in Virginia
May is the calmest stretch of the year at the reference station used for this state, Oceana Naval Air Station in Virginia Beach. Combined heating and cooling degree days for May come to about 198. That number needs context to mean anything: nationally, the lowest quietest-month figure found anywhere in the fifty states is around 70, and the highest is around 246. Virginia’s 198 sits well into the upper half of that range, closer to the states that never really stop asking for climate control than to the ones with a genuine dead zone in the calendar.
A degree day isn’t a temperature reading. It’s a measure of demand, a running tally of how far the outside air strayed from a comfort baseline over the course of a day, added up across the month. A month can average a pleasant afternoon temperature and still rack up a high degree-day total if mornings run cold and evenings run warm, because the system reacts to both ends of the day, not the average.
That’s exactly what’s happening in May here. A total of 198 is far from zero, and it rules out any idea of a full stop. There is no month on Virginia’s calendar where the house asks for nothing. May isn’t a pause, it’s a changeover, a stretch where the furnace or heat pump is winding down while the air conditioner is just beginning to wind up, with the two often overlapping in the same week rather than handing off cleanly. That’s a different situation from states with a true shoulder season, where the number drops toward that 70 floor and the mechanical systems can sit idle for weeks at a stretch. Virginia doesn’t get that luxury. The practical result: treat May and the surrounding weeks as a period of watchfulness rather than a vacation from thermostat decisions, because the next cool morning or warm afternoon is rarely more than a few days away.
Shutting the heat down for the year
Once the mornings stop dropping into furnace territory, most homeowners want to close out the heating system for the season. the Order Matters more than people assume, because doing it out of sequence can leave a system half-shut-down and confused when the first cold snap of fall arrives.
- Stop calling for heat at the thermostat rather than cutting power at the breaker or the switch. Letting the system respond to the setting, rather than yanking electricity, avoids leaving a blower or a valve mid-cycle.
- Let the system complete whatever cycle it’s already running before you touch anything else. A furnace or heat pump interrupted mid-cycle is more likely to need attention later.
- For any gas or oil-fired equipment, leave the fuel supply and pilot alone. Whether and how those get shut down for the season is governed by the manufacturer’s own guidance for that specific unit, not a generic seasonal habit.
- Inspect, clean, or change the air filter now, while the system is idle and the task is easy to remember. As U.S. ENERGY STAR puts it: “Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump.” That guidance covers all three pieces of equipment together, which matters if you run A Heat Pump and have been treating filter care as a furnace-only chore.
- Shut down the humidifier attached to the ductwork, if the house has one. It’s the single step almost everyone skips, because it isn’t part of the furnace itself and rarely gets a reminder.
- Clear anything stored against the furnace, vents, or return grilles over the summer, and vacuum out the registers while they’re easy to reach.
- Resist the urge to power the system down completely for the season. Virginia’s heating demand runs from October through May, roughly seven months of the year, and a late cold snap in early May or an early one in September is well within the normal range here. Keep the thermostat able to call for heat if needed, rather than leaving the house with no working line of defense against a sudden freeze.
The first run of the cooling season
The best day to test the air conditioner isn’t the first 90-degree afternoon of the year. It’s a mild day weeks before that, when a failed capacitor or a clogged drain line is an inconvenience rather than an emergency. Virginia averages about 26 days a year that hit 90 degrees or higher, and every one of those days is a bad time to discover a problem you could have caught earlier.
- Clear leaves, mulch, and overgrown plants away from the outdoor condenser unit, giving it open air on all sides.
- Check the condensate drain line and pan for clogs or standing water before the system runs for hours at a stretch.
- Change or wash the filter. As ENERGY STAR notes, “Airflow problems can reduce your system’s efficiency by up to 15 percent,” which means a system in perfect mechanical health can still underperform badly on a dirty filter alone.
- Run the system in COOL for a full cycle on a mild day, not a scorching one, so you can watch for short-cycling or weak airflow without discomfort forcing a rushed fix.
- Feel the air coming out of a register farthest from the unit, not the closest one. Weak airflow at the far end often shows up before it shows up anywhere else.
Most of that list applies directly here: 95% of Virginia homes run some form of air conditioning, and 83% run a central system, so the outdoor-unit and filter checks cover the large majority of houses. The remaining 17% rely on individual equipment, window units, wall units, mini-splits, or portables, where the equivalent check is simpler: clean or replace the unit’s own filter and make sure nothing blocks its intake or exhaust. Three out of four Virginia homes also run ceiling fans, which don’t replace any of this but do stretch the air conditioner’s reach on the mild days when a full cooling cycle isn’t needed yet.
The days that ask for both
May isn’t the only month that splits the difference. October does too. Using a plain convention stated here, not a published NOAA category, a month “asks for both” when it carries at least 50 heating degree days and at least 50 cooling degree days in the same thirty days. May, with about 85 heating degree days and 113 cooling degree days, clears both marks easily. October, with about 152 heating degree days and 57 cooling degree days, does the same. Those two months are when a house is most likely to call for heat at six in the morning and for cooling by mid-afternoon, in the same week and sometimes the same day.
The thermostat settings that make sense during those weeks aren’t the same ones that make sense in the dead of summer or winter.
| Approach | What it does | When it makes sense |
|---|---|---|
| Manual mode switching | You flip between HEAT and COOL by hand as the week’s weather shifts | When temperature swings are occasional, not daily |
| AUTO changeover | The thermostat switches modes on its own between a low and high setpoint | During May and October, when swings happen within the same day |
| Wide deadband | A gap of several degrees between the heating and cooling setpoints | Always, to stop the system from fighting itself |
| Open windows | No mechanical system running at all | Mild, low-humidity days when outdoor air alone keeps the house comfortable |
The expensive mistake shows up when the gap between the two setpoints is too narrow. If the heating setpoint is 68 and the cooling setpoint is 70, the furnace runs at dawn to hit 68, and by early afternoon the air conditioner kicks in to cool that same air back down to 70. The house pays twice for the same few degrees. A wider deadband, something closer to a five- or six-degree spread, gives the house room to drift naturally with the outdoor temperature before either system has to fire.
And the changeover in the other direction
The reverse happens on schedule. Virginia’s heating season begins in October, the first month whose average temperature drops below the 65-degree baseline used to count heating degree days, and demand peaks in January before the average climbs back above that line in May. That’s roughly seven months where the furnace or heat pump is the primary system in the house, bookended by the two changeover months already covered.
What matters locally is what’s actually installed. Furnaces are the main heating equipment in 56% of Virginia homes, and central heat pumps run another 27%, so most of the pre-season checklist here is furnace and heat-pump specific: filters, ignition components, and for heat pumps, the outdoor coil and refrigerant lines rather than a chimney or a boiler. Steam or hot-water boilers make up just 4% of homes, a real but small share, so radiator bleeding and boiler-specific prep apply to a minority rather than the majority. By fuel, electricity powers half of Virginia’s heating (50%), natural gas comes in at 36%, with propane and fuel oil filling in smaller shares.
The detail for that seasonal handoff, what to check before the first cold snap, how long to let a heat pump run before assuming it’s working, belongs in the heating-season guide on this site. This page’s job was narrower: to say plainly that in Virginia, the calendar never really stops, and the two weeks worth watching are the ones in May and October when the thermostat has to do double duty.