Sizing Guide
Through-the-Wall AC Sizing for NYC Apartments
Three things determine which through-wall unit you need: your wall sleeve dimensions, the room’s cooling load, and your electrical service. Get any one of these wrong and you’re returning equipment or, worse, paying for a unit that can’t do the job.
All GuidesStep 1
Measure Your Wall Sleeve
Grab a tape measure and get the inside dimensions of your wall opening — width and height. Not the grille on the outside. Not the unit currently sitting in there. The actual sleeve opening in the wall.
If there’s a unit installed, you can usually see the sleeve edges by looking at it from outside the building or by pulling the unit forward a few inches. If you can’t access it, check your building’s mechanical drawings or ask the super.
Common NYC Wall Sleeve Sizes
Step 2
Calculate Your BTU Requirement
The standard rule of thumb is 20 BTU per square foot of living space for cooling. But in NYC, that number needs adjusting based on real conditions that generic calculators ignore.
| Room Size | Base BTU | South/West Facing |
|---|---|---|
| 150–250 sq ft | 6,000–8,000 | 8,000–10,000 |
| 250–400 sq ft | 8,000–12,000 | 10,000–14,000 |
| 400–600 sq ft | 12,000–18,000 | 14,000–20,000 |
| 600–900 sq ft | 18,000–24,000 | 20,000–28,000 |
| 900–1,200 sq ft | 24,000–30,000 | 28,000–36,000 |
NYC-Specific Adjustments
- South and west-facing windows: Add 10-15% to the base BTU. Afternoon sun through NYC’s floor-to-ceiling glass walls turns a living room into a greenhouse.
- High ceilings: Pre-war apartments with 9-10 foot ceilings have 15-25% more volume than a standard 8-foot room. Size up accordingly.
- Top floor apartments: Add 10%. Roof heat load is real, especially in buildings without adequate roof insulation.
- Kitchen area: If the AC serves an open kitchen layout, add 4,000 BTU. Cooking generates serious heat that your living room unit has to overcome.
- Don’t oversize. An oversized unit short-cycles — it cools too fast, shuts off, and never dehumidifies properly. NYC summers are humid. A properly sized unit that runs longer will keep you more comfortable than an oversized one that blasts cold air and quits.
Step 3
Check Your Electrical Service
This is where NYC building replacements go sideways more than anywhere else. Every through-wall unit we carry runs on 208-230V/60Hz single-phase power. That matches the standard residential electrical service in NYC high-rises. But “standard” doesn’t mean “guaranteed.”
Electrical Checklist
- Verify your voltage. Most NYC residential buildings supply 208V or 230V to HVAC circuits. Check the breaker panel label or have an electrician verify. A unit rated for 208-230V handles both.
- Check the breaker amperage. A 1.5-ton condenser typically needs a 20-amp circuit with a Minimum Circuit Ampacity (MCA) of around 13 amps. A 2.5-ton unit may need 30 amps. The spec sheet for every unit lists MCA and Maximum Overcurrent Protection (MOP) — your breaker must match.
- Dedicated circuit required. Through-wall AC units must be on a dedicated circuit — nothing else on that breaker. If your apartment has the AC sharing a circuit with outlets, an electrician needs to fix that before installation.
- Wire gauge matters. 20-amp circuits use 12 AWG wire; 30-amp circuits use 10 AWG. If you’re upgrading from a smaller unit to a larger one, the existing wiring may not be adequate. A licensed electrician has to confirm this.
Common Sizing Mistakes in NYC Buildings
Mistake #1: Ordering by Ton Without Checking the Sleeve
“I need a 2-ton unit” is not enough information. A 2-ton PTAC chassis and a 2-ton through-wall condenser are completely different physical sizes. Know your sleeve first.
Mistake #2: Assuming All 208V Is the Same
Some older NYC buildings deliver true 208V from a three-phase panel, while others supply 230V from a single-phase service. The unit needs to be rated for the actual voltage at the outlet. All our units handle the 208-230V range, but if your building runs at 240V or 277V (some commercial conversions), you have a problem.
Mistake #3: Ignoring the Air Handler Side
For split systems, the outdoor condenser is only half the equation. You need a matching indoor air handler (fan coil unit) that’s properly sized and connected with the right refrigerant line set. Buying a condenser without planning the indoor side means you’ll be calling back for parts.
Mistake #4: Forgetting About Condensate Drainage
Every AC unit produces condensate water. In NYC apartments, that water has to go somewhere — usually a drain line to the building’s condensate riser or a condensate pump. If your building doesn’t have a condensate line near the unit, plan for that plumbing work during installation.
Matching Our Equipment to Your Needs
For buildings with 36″ x 19″ sleeves, here’s how our product lines map to room sizes:
For a detailed comparison of all Aerosys models, including specs and NYC sleeve compatibility, see our Aerosys TTWC Condenser Guide.
Need help figuring out which size is right? Use our sizing request form and we’ll match equipment to your space.
Send Us Your Sleeve Dimensions
Width, height, voltage, and room square footage. That’s all we need to tell you exactly which unit fits. We respond same-day.