AC Size Calculator Project Checklist

Introduction

Before you buy an air conditioner — or sign a contractor’s proposal — run through this checklist. It covers measurement, inputs, equipment selection, contractor vetting, and installation verification, in the order you’ll actually do them. Each item links to the guide with the full explanation. Start by getting your number from the AC Size Calculator, then check it here.

1. Measurements

• Conditioned floor area measured room by room (sq ft or m²) — garages and unconditioned spaces excluded.
• Ceiling heights recorded for each distinct area — not assumed at 8 ft (2.4 m).
• For mini-splits: each zone measured separately, not divided from a whole-home total.
• Large window areas noted with orientation (south/west glass is the load driver in the northern hemisphere).
• Units consistent throughout — no mixing sq ft and m² in the same calculation.
• Two-story homes: each floor measured separately, with a note that upstairs loads run higher (heat rises; roof adds gain).
• Sketch or photo record of the measurements kept — you’ll need them again when the contractor asks how you got your number.
• Room usage noted (bedroom vs. home office vs. rarely used guest room) — usage affects both load priorities and zoning decisions.
• Existing supply and return vent locations mapped — the duct layout constrains what a central replacement can actually deliver.

Technique details: estimating guide.

2. Load Inputs

• Climate band selected honestly (mild / moderate / hot) — borderline cases run both ways.
• Insulation rated by evidence (attic depth, window type, drafts), not optimism — the field checklist is in the estimating guide.
• Each adjustment factor applied exactly once — no stacked “safety” margins on top of conservative inputs.
• Internal gains added for home offices, server equipment, or heavy-cooking kitchens.
• Result converted to tons (BTU/h ÷ 12,000) and cross-checked in metric (m² × 215 BTU/h per m²).

Math reference: formula guide. Full process: complete guide.

3. Envelope First

• Attic insulation assessed — topping up is usually the cheapest load reduction available.
• Air sealing opportunities noted (outlets, window frames, attic penetrations).
• West/south glass shading considered (awnings, film, trees) before finalizing size.
• Load re-run after planned envelope improvements — size to the house as it will be.
• Sequencing confirmed: envelope work scheduled before the final load calculation, not after the equipment is ordered.
• Attic access and ventilation checked — insulation without ventilation traps moisture; both matter.

4. Equipment Selection

• System type matched to the situation: central (good ducts), mini-split (no ducts / zoning), window/portable (single rooms).
• Tonnage rounded to the nearest standard size — not rounded up “just in case.”
• Variable-speed / two-stage equipment considered for borderline estimates.
• SEER2/EER2 ratings compared at your electricity rate using the operating-cost formula (cost guide).
• Indoor and outdoor units matched — the SEER2 rating applies to the combination.
• Refrigerant type noted (R-32/R-454B in current equipment vs. phased-down R-410A).

Comparison: equipment guide.

5. Contractor Vetting

• Three quotes obtained, each based on a load calculation — not the old unit’s size.
• Manual J numbers provided in writing; total within ~15% of your own estimate.
• Manual S equipment selection shown — proposed capacity close to the calculated load.
• License and insurance verified; manufacturer certification checked for warranty purposes.
• Scope itemized: ductwork, electrical, permits, old-equipment disposal, commissioning.
• No red flags: no same-day pressure, no permit-skipping, no “biggest unit so you’ll never be hot.”

Full vetting process: DIY vs pro guide. Traps to avoid: common mistakes.

6. Installation and Handover

• Mechanical permit pulled (where required) and inspections scheduled — code compliance guide.
• Ductwork tested and sealed; leakage verified below 10% where ducts were part of the project.
• Refrigerant charge verified by a certified technician (subcooling/superheat readings).
• Airflow verified against manufacturer specs (static pressure check).
• Condensate drain tested and terminating in an approved location.
• Thermostat commissioned and homeowner walkthrough completed.
• Warranty registered (equipment + labor) and documentation filed.
• Load calculation, Manual J summary, equipment model numbers, and commissioning readings filed together — the next contractor or buyer will thank you.
• Permit finaled and inspection sign-off confirmed in writing — unclosed permits surface at sale time.

One final principle behind the whole list: sizing is the one part of the project where precision is free. An hour with a tape measure and honest inputs beats a decade of wrong-sized equipment. The common mistakes guide shows what happens when any of these steps get skipped.

7. First-Year Ownership

• Filters on a replacement schedule — monthly in heavy-use seasons, dated on the filter frame so you can tell at a glance.
• Outdoor coil rinsed each spring; vegetation kept 2 ft (60 cm) clear on all sides for airflow.
• Condensate drain checked each cooling season — algae tablets or a vinegar flush prevent the most common service call in the industry.
• First-summer performance noted: does the system hold the setpoint on the hottest afternoons with long, steady cycles? Short cycling or lost ground in year one is a warranty conversation, not a “wait and see.”
• Energy bills compared against the pre-purchase operating-cost estimate — large discrepancies are worth a commissioning re-check.

Ongoing maintenance is mostly filter changes and coil cleanliness — the unglamorous work that protects the sizing investment. A right-sized system that’s never maintained slowly becomes a wrong-performing one.

Related Guides

• Complete Guide — how AC sizing works, adjustment factors, and a fully worked example.
• Common Mistakes — the errors that produce wrong-sized systems, and how to avoid each one.
• Estimating Guide — how to measure rooms and assess insulation, windows, and exposure.
• FAQ — quick answers to the most asked sizing questions.
• Pro Tips — trade wisdom for getting the sizing right the first time.

Get Your Number

A checklist is only useful against a real project — run your home through the AC Size Calculator, then work this list top to bottom before you spend anything.

Disclaimer: Calculator results are planning estimates, not a substitute for a professional load calculation. Proper equipment sizing should be based on a Manual J load calculation performed by a licensed HVAC contractor; verify requirements with a local professional and your local building code.