In Vermont, the honest answer is: briefly, and only in June. That’s the single month when the state’s combined heating and cooling demand drops low enough for both systems to sit idle at once, according to 30 years of NOAA climate data. It’s a short window, bracketed by a heating season that starts building again by September. Here’s when to shut one system down, when to start the other, and what to do with the weeks that ask for both.
The quietest month in Vermont
June is the quietest month in Vermont’s heating and cooling year, with a combined total of about 172 degree days. That figure needs a quick explanation: a degree day isn’t a temperature, it’s a measure of demand, calculated by comparing the day’s average temperature against a 65-degree baseline. The higher the number, the harder a furnace or an air conditioner has had to work that month.
Placed against the rest of the country, 172 sits closer to the middle of the national range than to either edge. The mildest states see a quiet month drop as low as about 70 degree days; the busiest still run around 246 in their calmest stretch. Vermont’s June lands well above that low end, which means this isn’t the dead calm found in a coastal climate that rarely gets extreme, but it’s still a real dip compared to the months on either side of it.
That makes June a genuine pause, not just a changeover with a different name. There’s enough slack in demand for both a furnace and an air conditioner to sit idle for stretches at a time, which is exactly the window the rest of this page is built around. Vermont’s year has a long cold shoulder on one side and a short, sharp cooling season on the other, and the demand curve follows that shape: heating dominates most months, cooling shows up as a brief mid-summer spike, and the two overlap only briefly in the transition months.
For a homeowner, that translates into a narrow but usable opportunity. June is the best month to handle maintenance on both systems without worrying about a sudden swing catching the house off guard, not because nothing ever runs in June, but because demand is lower here than at any other point on record. It’s the moment the furnace has almost certainly finished its work for the year and the air conditioner hasn’t yet been asked to do much of its own, which is a different situation from a state where the quiet stretch runs for weeks with almost nothing running at all.
Shutting the heat down for the year
Vermont’s heating season runs roughly nine months, September through May, so by the time June arrives the risk of a cold snap catching an empty house has passed. This is a part of the country where shutting the heating system down completely for a few months carries no frozen-pipe risk, unlike doing the same thing in the middle of winter.
- Turn the thermostat down so it stops calling for heat, rather than cutting power at the breaker or switch, so controls power down in the order they’re designed for.
- Let the system finish its current cycle instead of interrupting it mid-run.
- If the system burns oil, natural gas or propane, leave the shutoff valve and pilot assembly alone. Follow the manufacturer’s guidance for that specific unit rather than treating it as a routine seasonal step.
- Shut down any humidifier mounted on the ductwork. It’s tied to the heating system and almost always forgotten once the furnace stops, left sitting with standing water for months.
- Replace or clean the air filter before closing up. ENERGY STAR’s guidance is direct: “Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump.” A fresh filter at shutdown means one less thing to remember in the fall.
- Clear the area around the unit, vacuum registers, wipe down the cabinet, and move anything stored too close to a boiler or furnace over the summer.
None of this touches the fuel supply itself. Thermostat, filter, humidifier and housekeeping are fair game for a homeowner; anything involving the gas line, oil line or a standing pilot follows whatever the manufacturer’s manual says, full stop.
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 earlier, when a dead capacitor or a clogged line is an inconvenience instead of an emergency. Fixing a problem on a cool spring day means one trip to sort it out. Finding the same problem during the first heat wave means living with a hot house while parts get sorted.
What to check first
- Clear at least two feet around any outdoor unit, central condenser or mini-split, so leaves and mulch aren’t blocking airflow.
- Check that the condensate line drains freely, a blocked line is a common cause of a system that runs but doesn’t cool.
- Change or wash the filter, whether it’s a central return filter or a slide-in filter on a window unit.
- Run the system in COOL for a full cycle on a mild day, not a hot one, long enough to reach the set temperature.
- Feel the air at a register or vent farthest from the unit, not the closest one, weak airflow shows up there first.
ENERGY STAR puts a number on why the filter step matters: “Airflow problems can reduce your system’s efficiency by up to 15 percent.” That’s true whether the air is pushed through ductwork or blown straight out of a window unit’s own housing.
What’s actually installed here
Vermont’s numbers point in a clear direction. Statewide, 67% of homes use some form of air conditioning, but only 7% run a central unit with ductwork and an outdoor condenser. The other 60% run individual equipment, a ductless mini-split, a window unit, a wall unit or a portable — and 58% of homes also run ceiling fans, often alongside or instead of mechanical cooling. In a house with a window or wall unit, there’s no condenser pad to clear and no ductwork to inspect; the filter and drain path carry most of the weight. Central air, the minority setup here, is the one case where the full five-step list applies as written.
The days that ask for both
Anyone who’s turned the thermostat up in the morning because the house felt chilly, then switched it to cooling by mid-afternoon because the same house had gone stuffy, has lived through what the degree-day numbers call a month that asks for both. In Vermont, that’s September: 134 heating degree days and 66 cooling degree days in the same 30 days, by the 1991-2020 normals.
The convention behind that label is worth stating plainly, since it isn’t a category NOAA publishes: a month counts as asking for both, here, when it reaches at least 50 heating degree days and at least 50 cooling degree days at the same time. September clears both. It isn’t a contradiction in the data, it’s a month where cool nights push heating demand up while warm afternoons keep cooling demand alive.
| Approach | What it does | What it costs |
|---|---|---|
| AUTO changeover mode | Switches between heating and cooling automatically as indoor temperature drifts | Convenient, but a narrow gap between setpoints lets the system heat in the morning and then cool that same air by afternoon |
| Wide deadband between setpoints | Sets the heating point several degrees below the cooling point, leaving a buffer where neither runs | Some hours feel less than ideal, but avoids paying to heat air the system is about to cool |
| Open windows | Uses outside air directly when it falls between the two setpoints | Free, but only works without much humidity or wind |
The mistake worth naming is the narrow gap. Set the heating point to 68 and the cooling point to 70, and a September morning heated to 68 can get pushed to 71 by afternoon sun, triggering cooling and throwing away the heat just paid for. Widening that gap, say a 66-degree heating point and a 74-degree cooling point, lets the house drift with the outdoor temperature before either system has to run, on the mildest September days, that gap alone can mean neither one turns on.
And the changeover in the other direction
The reverse changeover doesn’t wait long. Heating demand starts building again in September, the first month whose average temperature normally dips below the 65-degree mark NOAA uses to count heating degree days. From there it climbs fast, through 459 degree days in October and 773 in November, peaking in January, before easing back down and slipping under that 65-degree line again in June.
That makes the cooling window in Vermont genuinely short, compressed compared to much of the country. The autumn checklist, shutting down the air conditioner and prepping the heating system, belongs on this site’s dedicated heating-season guide, but the timing worth flagging here is that in Vermont, that guide is worth reading closer to Labor Day than to Halloween.
What that guide should focus on locally follows from what’s actually installed. In Vermont, 51% of homes heat with a furnace and 25% with a steam or hot-water boiler, a larger boiler share than most states carry. On fuel, 46% of homes run on fuel oil or kerosene, more than the 21% on natural gas, with propane at 13% and electricity at 6%; the state’s central heat pump share wasn’t published, a suppressed estimate rather than a sign that none exist. A furnace-heavy fall checklist centers on filters and ductwork, while the quarter of Vermont homes running a boiler need theirs built around venting, bleeding radiators and the oil or propane supply instead.