Montana never fully powers down. June comes closest to a quiet month, but it still adds up to roughly 170 combined heating and cooling degree days, not zero. The real question isn’t whether to shut the system off entirely, it’s knowing the order of steps for shutting the furnace down, starting the air conditioner, and surviving the weeks when the house wants both.
The quietest month in Montana
June is the calmest stretch of the year here, and even then the house racks up about 170 heating and cooling degree days combined. Degree days measure demand, not temperature: they tally how far the daily average strays from a 65 F baseline, added up over the month. A high number means the equipment worked hard; a low one means the house barely noticed the weather at all. For scale, the calmest month anywhere in the fifty states runs about 70 degree days, and the highest calmest-month figure tops out near 246. Montana’s June sits well above that low end, closer to the middle of the national range.
That placement matters. A month with a total near 70 is a genuine lull, weeks where the thermostat sits untouched and nobody thinks about the vents. A month near 170, on the other hand, is a house still working, just less than it does in January or July. There is no month on Montana’s calendar where the system asks for nothing.
What the shape of the year actually looks like
Winter here runs long and heavy. The cold season stretches from early fall through late spring, with a hard core of deep demand in the dead of winter. Summer, by contrast, is short and sharp: a compressed handful of weeks where the heat load builds fast, peaks, and falls off again almost as quickly as it arrived. There’s no long, gentle plateau in either direction. The furnace runs for months on end, the air conditioner runs hard for a shorter stretch, and the space between the two is thin rather than restful.
Summer heat, when it shows up, isn’t mild. The reference station in this state averages about 28.3 days a year at 90 F or hotter, enough to stress plants, push water demand, and make an undersized or poorly maintained cooling system show its limits. That’s the backdrop against which June’s modest degree-day total should be read: it’s a brief calm before a short, intense push, not a season unto itself.
Shutting the heat down for the year
Given how long Montana’s heating season runs, the shutdown deserves to be done in order, not just flipped off at the breaker. Doing it out of sequence is how a fuel-burning appliance gets left in a half-checked state, or a filter gets forgotten until the first cold morning of fall.
- Stop calling for heat at the thermostat first. Set it above the current indoor temperature, or switch it to COOL or OFF, rather than cutting power to the furnace directly.
- Let the system finish its current cycle and shut down naturally, rather than interrupting a blower or a burner mid-run.
- For any fuel-burning furnace or boiler, leave the shutdown and inspection of burners, pilot systems, and gas connections to the manufacturer’s guidance and, where called for, a qualified technician. This is not a routine do-it-yourself step.
- Change or clean the filter before the system sits idle for months. 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, not just the furnace, which matters if the house also runs a heat pump.
- Shut down any humidifier mounted to the ductwork. It’s the step almost everyone forgets, and a humidifier left running dry or unattended over the summer is a common source of mid-season repair calls.
- Vacuum registers, clear anything stacked in front of vents, and check that nothing was pushed against the furnace or boiler over the winter that would block airflow when it starts up again.
One thing this state’s climate rules out: turning the heat off entirely as a way to save money over the summer. Montana’s heating season stretches across roughly ten months of the year, and freeze risk to plumbing is a real concern well outside the deep-winter months. The shutdown above is about stopping the system from cycling unnecessarily, not about leaving a house with no heat source available if a cold snap arrives early.
The first run of the cooling season
Start the air conditioner on a mild day, well before the first genuinely hot one. That’s the whole point of doing it early: if a capacitor is weak, a filter is clogged, or a condensate line is blocked, you find out on a 70-degree afternoon instead of during a 95-degree emergency, and there’s time to get it fixed before it matters.
- Clear leaves, grass clippings, and anything else piled against the outdoor unit, and give it a couple of feet of open space on every side.
- Check the condensate drain line for clogs. A blocked line is one of the most common reasons a cooling system trips off or leaks indoors on its first run.
- Change or wash the filter, whether that’s a central system’s return filter or the washable filter in a window or ductless unit.
- Run the system in COOL for a full cycle on a mild day and listen for anything unusual before the heat arrives.
- Feel the air at a register farthest from the unit, not the nearest one, to confirm airflow is reaching the whole house and not just the closest room.
Montana’s cooling equipment is a mixed picture. Statewide, about 65% of homes have some form of air conditioning, but only 40% run a central system. The remaining 30% rely on individual equipment: ductless mini-splits, window units, wall units, or portables. That gap matters for this checklist. A window or Mini-Split household skips the outdoor-unit-and-ductwork steps almost entirely and instead focuses on the unit’s own filter, a secure mount, and a clean seal around the frame. A central-air household needs the full list above, including the condensate line and the airflow check at a distant register.
Whichever setup a house runs, the filter step earns its keep. As ENERGY STAR notes: “Airflow problems can reduce your system’s efficiency by up to 15 percent.” A system that starts, cools, and seems fine can still be quietly underperforming if the filter was never addressed at the start of the season.
The days that ask for both
Anyone who has felt a Montana house call for heat at six in the morning and for cooling by three in the afternoon in the same week isn’t imagining it. Two months on this state’s calendar genuinely ask for both: June and September. Using a threshold of at least 50 heating degree days and at least 50 cooling degree days in the same month, a convention stated here rather than a category NOAA publishes, June (90 heating, 81 cooling) and September (168 heating, 62 cooling) both clear that bar. It isn’t a contradiction. It’s a house that needs a little warmth before sunrise and a little cooling in the afternoon, in the same 24 hours.
How the thermostat is set during those weeks decides whether that swing costs money or barely registers.
| Setting | What it does | What it costs or saves |
|---|---|---|
| AUTO changeover, narrow gap between setpoints | Switches between heat and cool automatically whenever the temperature drifts past either setpoint | Can heat the house in the morning, then spend energy cooling that same warm air by afternoon |
| AUTO changeover, wide deadband (several degrees between heat and cool setpoints) | Lets the house drift naturally within a comfortable range before either system kicks on | Cuts down on the back-to-back heat-then-cool cycle that wastes energy |
| Windows open, systems off | Uses outdoor air directly instead of either system | Free, and often the better answer on the mild days both June and September tend to produce |
The mistake worth avoiding is a narrow gap between the heating and cooling setpoints during these transitional months. Set them too close together, and the furnace warms the house early in the day, only for the air conditioner to spend energy cooling that same air a few hours later. Widening the gap, or simply opening windows on the mild afternoons these two months tend to produce, avoids paying twice for the same few degrees.
And the changeover in the other direction
Montana’s heating season begins in September, the first month whose 30-year average temperature (61.4 F) drops below the 65 F baseline NOAA uses to count heating degree days. Demand climbs fast from there and peaks in January, at 1,180 degree days, before easing back through spring and finally dropping below that baseline again in July. In practical terms, that means the reverse changeover, air conditioner down, furnace up, tends to land in the September to October window, right around the same weeks the house is still occasionally asking for a little cooling on a warm afternoon.
What that pre-season check should focus on depends on what’s actually installed. Furnaces run in about 65% of Montana homes, making the furnace the equipment most readers here will be prepping, with natural gas as the leading fuel at 59% of households and electricity at 24%. But a meaningful slice, about 10%, run a steam or hot-water boiler instead, and that’s a different pre-season routine entirely, involving bleeding radiators and checking circulator pumps rather than furnace filters and ductwork. Propane heats another 9% of homes, mostly in areas without natural gas service. The detailed step-by-step for that transition, including what changes for boiler households versus furnace households, belongs in the heating-season guide for this state, which is the natural next stop once the cooling season starts winding down.