My ConEd bill hit $340 last August. This was not a surprise the way a car accident is a surprise — I’d been running two window units through a heatwave week and I knew it was going to hurt. But it clarified something I’d been vaguely aware of for years without acting on: I had no idea what I was doing.
I’d read the summer cooling articles. Keep the thermostat at 78°F or above. Use ceiling fans to extend the cool air. Close the blinds. All fine advice. Also, almost useless for the situation I was in: a Greenpoint apartment, two window units, and a utility that charges substantially more for electricity in the afternoon than at night.
The standard cooling advice is written for homeowners with central HVAC and programmable thermostats. It does not address the question that matters if you live in an apartment with window units — when are you running them?
Summer pricing starts June 1 and most people don’t plan around it
ConEd’s residential rates go up every June 1. From June through September, rates are higher across the board, regardless of which rate plan you’re on. On top of that baseline, ConEd’s Time-of-Use plan puts super-peak hours at 2–6 PM on weekdays, June through September — roughly 2.5 times the off-peak rate, which runs from 10 PM to 8 AM on weekdays and all day on weekends.
I wasn’t on the Time-of-Use plan last summer. I didn’t need to be for the lesson to apply. Standard rates still cost more during summer months, and the hottest part of the day tends to overlap with the most expensive part of the day for most US utilities, not just ConEd. Check your utility’s rate schedule and you’ll usually find the same structure: afternoon is expensive, early morning is cheap.
Running a standard 8,000 BTU window unit eight hours a day costs roughly $30–40 per month at the national average electricity rate of $0.16/kWh. In New York, rates are closer to $0.25–0.30/kWh, pushing that number to $50–70 per month per unit. Run both units primarily during peak afternoon hours and you’re paying a premium on top of that.
I had two units. I was running both of them from roughly noon to midnight — almost perfectly calibrated to maximize cost.
My sister’s electric bill versus mine
My sister lives in a studio in Astoria. Same utility as me. Her July bill last year was $78. Mine was $210.
She was not suffering through August to achieve this. She pre-cools.
Her routine: run the AC from 7 AM until about 1 PM, pull the room down to 70°F, close all curtains facing south and west before noon, then turn the unit off. Her apartment holds that temperature until at least 4 PM on most days. She turns the unit back on in the early evening if needed, by which point outside temperatures have dropped enough that the unit runs less to get back to comfortable.
I thought this sounded miserable. I was wrong. I tried a version of it in September 2024 — late in the season, with temperatures already dropping — and still cut $45 off my bill compared to September 2023 on similar-temperature weeks. That got my attention.
Why pre-cooling works when thermostat advice doesn’t
The 78°F recommendation from the Department of Energy makes sense for central air. The logic: a higher setpoint means your HVAC cycles less frequently and uses less energy over the full day. The system is managing a whole home’s thermal mass.
Window units work differently. They cool one room aggressively and then cycle off. There’s no whole-house thermal mass to regulate, no ductwork distributing conditioned air to equalize temperatures. When a window unit is told to maintain 78°F in a room that’s been heating up since noon, it runs continuously and still can’t get ahead.
Pre-cooling inverts the logic. You run the unit hard during cheap-rate morning hours when outside temperatures are still manageable — say, 65°F at 7 AM — and pull the room down to 68–70°F. Heat transfer through walls and windows is slow. A room pre-cooled to 70°F at 11 AM will stay below 76°F until at least 3 PM in most apartments, without the AC running at all.
Some apartments hold cold better than others. Top-floor units, west-facing windows, thin 1960s construction — these all shorten how long a pre-cool holds. Conditions vary. But even in harder-to-cool spaces, the strategy reduces how many hours you’re running the unit during expensive afternoon hours.
Window unit sizing and the panic-buy problem
Summer is when people buy air conditioners badly. They walk into Home Depot in July, sweating through their shirt, and buy the biggest unit on the shelf.
This backfires. An oversized window unit cools the air too quickly, doesn’t run long enough to remove humidity, then cycles off — leaving the room cold but clammy. Humidity is what makes a hot room feel unbearable in the first place. A properly-sized unit that runs for longer cycles removes substantially more moisture from the air.
For a standard 10×12 bedroom, 5,000 BTU is enough. For a 250–300 square foot studio or open living area, 8,000 BTU. The rule of thumb is roughly 20 BTU per square foot; you can find proper charts on energystar.gov that account for ceiling height, sun exposure, and whether the room is a kitchen.
I ran a 10,000 BTU unit in my 150-square-foot bedroom for three years. Replaced it last summer with a 5,000 BTU unit that cost $130 at Target. My bedroom is more comfortable and my bill dropped about $18 per month on that room alone. Three years of wasted money is a frustrating thing to calculate.
The fan math and what it buys you
Ceiling fans cost about a penny an hour to run. Window units cost $0.10–0.20 per hour. The DOE’s figure is that running a fan alongside AC lets you raise the thermostat setting by about 4°F with equivalent perceived comfort — moving air feels cooler on skin than still air at the same temperature.
For window units in an apartment, the most useful application isn’t during the AC run itself. The fan helps extend how long you stay comfortable after turning the unit off. Post-pre-cool, with the room at 70°F, a fan in the hallway circulating air between rooms can push back the point where you need to turn the AC on again by an hour or more.
I have a box fan in my hallway set up for exactly this, moving air between the bedroom and the living room. I couldn’t tell you if my airflow setup is aerodynamically optimal. What I know is my second unit runs noticeably less since I started doing it — probably 30–40% fewer hours per day.
The fan costs less than $1 per month to run. The tradeoff is worth it.
What I’m doing this summer
The plan for 2026: run both units from 7–11 AM on weekdays when the electricity rate is at its lowest and outside temperatures are still manageable. Close south- and west-facing curtains before noon. Use the box fan to circulate air through the afternoon. Run the AC again in the evening if the apartment climbs above 76°F, which happens less often than you’d expect if you’ve done the morning pre-cool properly.
My July 2025 bill was $187 on this approximate schedule, versus $210 in July 2024. My goal this summer is to stay under $160, which means being more consistent about starting the pre-cool before 8 AM rather than drifting to 9 or 10.
The $340 August was costing me roughly $150 more than it needed to. The air conditioning wasn’t the problem. Running it at 2 PM instead of 7 AM was the problem.
One thing I haven’t figured out: whether to run a dehumidifier alongside the AC on moderately humid days, or instead of it. Both draw electricity. The math is murkier and I haven’t landed on an answer. If you’ve worked this out in a New York apartment, I’d like to hear it.