Introduction
The difference between a trustworthy cooling load and a guess is rarely math — it is thoroughness. Miss the west windows, forget the home office, or leave infiltration at a software default, and the result quietly drifts by half a ton or more. This checklist walks through every input in the order a technician would capture it, so nothing gets skipped. Print it, work it with a tape measure using the techniques in our estimating guide, then enter the results into the cooling load calculator.
Building Geometry
- Conditioned floor area measured (sq ft) — garages and unconditioned spaces excluded
- Ceiling height per floor recorded (air volume = area × height)
- Number of stories and floor plan sketch completed
- Foundation type noted (slab, crawlspace, basement — conditioned or not)
Windows and Glazing
- Every window measured (width × height) and assigned to north, south, east, or west elevation
- Skylights measured and assigned to their roof-slope orientation
- Glass type identified per elevation (single, double clear, double low-E, triple) with SHGC noted
- Exterior shading recorded: overhangs, awnings, solar screens, mature trees per elevation
- Doors with significant glazing included in the window schedule
Envelope and Insulation
- Wall construction and R-value recorded (2×4 ≈ R-13, 2×6 ≈ R-19–R-21, masonry noted)
- Attic insulation type and depth measured; R-value calculated (see our materials guide for per-inch values)
- Roof color and material noted (dark roofs run significantly hotter)
- Floor/crawlspace/basement insulation status recorded
- Air sealing status assessed — known draft points, recessed lights, attic penetrations
Internal Gains
- Typical daytime occupancy counted (actual people, not bedrooms)
- Home-office equipment inventoried (computers, monitors — watts × 3.412 = BTU/hr)
- Lighting wattage summed room by room
- Kitchen equipment noted (gas vs. electric range, refrigerator duty cycle)
- Other heat sources listed: TVs, gaming, aquariums, dehumidifiers, workshop tools
- Realistic usage schedules applied — not everything runs at once
Infiltration and Ventilation
- Construction era and tightness assessed (or blower-door ACH50 used if available)
- Window/door replacement history factored into leakage assumptions
- Mechanical ventilation inventoried: bath fans, range hood CFM, ERV/HRV if present
- Assumption documented — and sensitivity checked one step tighter and looser
Design Conditions
- Local 1% summer design temperature looked up (not the record high)
- Indoor setpoint chosen (typically 75°F / 24°C)
- Temperature difference (ΔT) confirmed for conduction calculations
- Outdoor design humidity noted for the latent calculation
Calculation and Verification
- All five load components computed: envelope, solar, internal, latent, infiltration
- Total in BTU/hr divided by 12,000 for tons
- Metric cross-check: BTU/hr × 0.29307 ÷ 1,000 = kW, and tons × 3.51685 = kW — both agree
- Sensible heat ratio calculated (sensible ÷ total) for equipment matching
- Result sanity-checked against climate norms (see the complete guide table)
- Every assumption written down for the next person who revisits the number
- Result compared against contractor bids — deviations questioned, not accepted
Before You Buy Equipment
- Envelope upgrades evaluated first — re-calculate after improvements, not before
- Duct system assessed (Manual D) rather than upsizing to compensate for duct losses
- Equipment selected per Manual S: capacity at design conditions, sensible heat ratio matched
- Code/permit documentation confirmed with the local AHJ where required (see our code compliance guide)
- Final number reviewed against the common mistakes list — no rule-of-thumb sizing, no nameplate copying
Common Gaps This Checklist Catches
Run through this list and you will avoid the omissions that most often corrupt a calculation. The usual suspects, drawn from our mistakes guide: west and east glazing lumped in with north glass (worth 8,000+ BTU/hr of error in a typical home); the home office that never got counted (two workstations add ~1,500–2,000 BTU/hr); infiltration left at a software default after new windows were installed (overstates the load by thousands of BTU/hr); and the design temperature copied from a record heat wave instead of the 1% design value (bakes in phantom capacity). Each of these is a five-minute fix at the measuring stage and an expensive surprise at the equipment stage. The checklist also forces the metric cross-check — BTU/hr to kW and tons to kW must agree — which catches the decimal-point slips that no amount of careful measuring can prevent. Finally, the documentation line item matters more than it looks: loads are revisited at every equipment replacement and every addition, and an undocumented number from five years ago is indistinguishable from a guess.
Using the Checklist With a Contractor
Bring the completed checklist to bid meetings. A contractor who welcomes it — who walks through your window schedule, questions your infiltration assumption, and shows you their own Manual J inputs — is a contractor you can trust. One who waves it away and quotes from the old nameplate has told you everything you need to know. The checklist is also the natural companion to a professional engagement: hand your measurements to the Manual J provider as a starting point, and their site visit becomes a verification pass rather than a from-scratch survey, which some providers will reflect in a lower fee. Whether the final number comes from your calculator or theirs, the discipline is the same — every input captured, every assumption written down, every conversion cross-checked.
Related Guides
- Estimating Guide — measuring every input on this checklist.
- Complete Cooling Load Guide — the full overview with a worked example.
- Cooling Load Formulas Explained — the math behind each line item.
- Pro Tips — field-tested habits for accurate results.
- Cooling Load FAQ — twelve detailed answers to common sizing questions.
Get Your Number
A checked box is only useful once it becomes a number. Transfer your checklist results into the cooling load calculator and get the BTU/hr, tonnage, and kW figure your project deserves — a careful hour with this checklist beats a careless minute of guessing every time — and it gives every contractor bid a benchmark to meet.
This checklist is planning guidance for educational purposes. Actual cooling loads depend on site-specific construction, shading, occupancy, and climate data — verify your results with a licensed HVAC professional before purchasing equipment, and consult your local building authority for any code-related decisions.
