September is the closest New Jersey gets to a break, but “closest” isn’t the same as “off.” The state’s quietest month still totals about 193 combined heating and cooling degree days, so the honest answer is timing, not silence: shut heating down as spring settles in, bring cooling up on a mild day before the first real heat wave, and expect a stretch in between where the house asks for both.
The quietest month in New Jersey
Degree days aren’t a temperature reading. They measure how far the daily average strays from 65 F, added up over the month, which is why a “quiet” month can still carry real demand if the days swing wide even when the average looks mild. In New Jersey, that quietest month is September, at roughly 193 combined heating and cooling degree days.
Set against the rest of the country, that number sits well toward the demanding end. The lowest quietest-month total anywhere in the fifty states runs around 70; the highest runs around 246. New Jersey’s 193 lands closer to the high side of that range than the low one.
What that means in practice: there is no month here when the house asks for nothing. A state with a quietest month near 70 gets stretches where the thermostat can sit untouched for weeks. New Jersey doesn’t get that. September is calmer than January or July, but it’s a changeover month, not a true pause, with mornings cool enough to call for heat and afternoons warm enough to call for cooling on the same day. Plan around that instead of waiting for a window that the numbers don’t support.
Shutting the heat down for the year
Do the shutdown in stages rather than in one motion, and start at the thermostat, not the breaker or the fuel line.
- Turn the thermostat down (or to a non-heat mode) so the system stops calling for heat, rather than cutting power outright.
- Let the current cycle finish so the blower or circulator pump completes its run instead of stopping mid-cycle.
- Leave any fuel-burning components, gas valves, pilot assemblies, and igniters, to the manufacturer’s guidance rather than servicing them yourself.
- Inspect, clean, or change the filter. ENERGY STAR’s standing advice is to “inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump,” and the shutdown is a natural checkpoint even if it’s not the calendar month.
- Shut down and drain any humidifier fitted to the ductwork. It’s the one step almost everyone forgets, and a stagnant, undrained humidifier over the summer is how odors and scale build up.
- Clear registers, vents, and the area around the furnace or boiler of anything stacked against them over the winter.
New Jersey’s heating season runs about eight months, October through May, based on the point where the monthly average temperature crosses back above the 65 F baseline. By the time this shutdown makes sense, overnight lows are safely clear of freezing, so powering the system fully down carries no risk of frozen plumbing. That would not be true in January or February.
The first run of the cooling season
Do this on a mild day, not the first 90-degree afternoon. A failed capacitor or a clogged condensate line found in advance is an annoyance; the same fault discovered during a heat wave is a wait for a callback with no relief in the meantime.
- Clear debris, leaves, and overgrown plantings from around the outdoor condenser unit.
- Check the condensate drain line for clogs before the system runs under real load.
- Change or wash the filter, following the same ENERGY STAR guidance used at shutdown.
- Run the system in COOL for a full cycle on a mild day, watching for it to reach the set temperature and shut off normally.
- Feel the airflow at a register farthest from the unit, not the closest one, to catch weak duct delivery early.
ENERGY STAR also notes that “airflow problems can reduce your system’s efficiency by up to 15 percent,” which is the case for the filter check even when nothing sounds or looks wrong.
What applies locally depends on the equipment. Statewide, 96 percent of New Jersey homes run some form of air conditioning, but only 61 percent run a central system with an outdoor condenser to clear. The rest, a sizable 35-point gap, run window, wall, portable, or Mini-Split units, where the outdoor-unit check still applies to mini-splits but not to window or wall units, and the filter step matters for all of them. Sixty-three percent of homes also use ceiling fans, which don’t replace this checklist but do stretch the comfort a central or individual system provides.
The days that ask for both
This is the week the thermostat earns its keep: heat calling at six in the morning, cooling calling by mid-afternoon, same house, same day. In New Jersey, that’s May, the one month that crosses a working threshold of at least 50 heating degree days and at least 50 cooling degree days in the same 30-day stretch (124 and 69, respectively). That threshold isn’t a NOAA category; it’s a line drawn here to describe exactly this pattern, and May clears it comfortably.
| Situation | What to do |
|---|---|
| Cold mornings, warm afternoons | Use a wide deadband between the heating and cooling setpoints, so neither system fires to close a gap of a degree or two. |
| Thermostat set to AUTO changeover | Convenient, but it can flip modes more often than needed if the deadband is narrow, running both systems more than the day requires. |
| Mild, low-humidity afternoons | Open the windows instead of switching to cooling; it costs nothing and often does the job in May. |
| Narrow gap between setpoints | Avoid it. It’s the expensive mistake: the house heats in the morning, then cools that same air a few hours later. |
The fix isn’t a smarter thermostat, it’s a wider gap between the two setpoints and a willingness to let the house drift a degree or two before either system responds.
And the changeover in the other direction
Heating demand in New Jersey builds back once the monthly average temperature drops below that same 65 F line, which happens in October, and it climbs fast, October’s degree days are already several times September’s before peaking in January. That’s the window to reverse this whole checklist, not the first frost.
What to check first depends on what the house actually runs. Sixty-one percent of New Jersey homes heat with a furnace, but a notable 25 percent run a steam or hot-water boiler, a much higher share than most states, and only 3 percent run a central heat pump. Natural gas fuels 75 percent of homes, electricity 16 percent, fuel oil or kerosene 7 percent; propane wasn’t published as a reliable state estimate, which means suppressed data, not zero. A furnace household is mainly a filter-and-igniter check. A boiler household needs the radiators bled and system pressure checked, a step furnace guides don’t cover and boiler owners often skip. That fall changeover, with its own order of operations, is the subject for the heating-season guide on this site.