Tool
Prepare for your AC sizing visit
This tool does not size your AC. It builds a one-page prep sheet with the facts a contractor's Manual J load calculation needs, so every quote is sized from the same information.
Build your prep sheet
The tool itself sends nothing to us; your entries stay in this tab. Site analytics are described in the privacy policy.
How to use the sheet
- Give the same sheet to every contractor who visits.
- Ask each to run a Manual J and give you the result in writing: the heat gain in Btu/h and the size they chose.
- If two quotes differ by a ton or more, ask each to explain the difference.
ACCA Manual J (ANSI/ACCA 2, 8th edition) is the American National Standard for residential heating and cooling load calculation. Dallas enforces the 2021 International Residential Code and 2021 IECC with Dallas amendments, effective 12 May 2023. The IRC requires equipment to be sized from a load calculation (ACCA Manual J) rather than a rule of thumb.
Why each question matters
A load calculation estimates how much heat enters the house on a design day, room by room. The questions on the sheet are the inputs that move that number most, so a contractor who receives them can spend the visit checking rather than guessing.
| Input | Why it matters for cooling load |
|---|---|
| Floor area | The starting point, but only one input. Two houses of the same size can need different systems. |
| Ceiling height | Taller and vaulted ceilings add volume and wall area exposed to heat. |
| Air handler location | Equipment and ducts in a Texas attic sit in very hot air, so duct gains and losses matter more. |
| Attic insulation | The ceiling is a large heat path in a single-story house; thin insulation raises the load. |
| Windows and their direction | Sun through glass is a major gain. West-facing glass takes the late-afternoon sun, when outdoor temperatures peak. |
| Year built | A rough guide to the construction, insulation and duct practice of the period. |
| Problem rooms | Point to duct or room-level issues that a bigger unit will not fix. |
Dallas heat raises the stakes. DFW averages 20 days a year at or above 100 °F on the 1991–2020 normals, two more than on the 1981–2010 normals. A system has to keep up on those days while still running long enough on ordinary summer days to pull moisture out of the air.
How to find the answers in twenty minutes
- Floor area: use the appraisal district record, a recent appraisal or the listing from when you bought. Count only the space the system cools.
- Ceiling height: measure one room with a tape. Note any vaulted living room separately.
- Air handler: follow the return grille or the thermostat wiring; it is usually in the attic, a hall closet or the garage.
- Insulation: from the attic hatch, look at the depth of loose fill or batts between the joists. If you can see the tops of the joists, choose "little or none".
- Windows: look for two panes and a spacer at the edge of the glass. Mixed is common after partial replacements.
- Sun: note which wall has the most glass and whether trees or a porch shade it in the afternoon.
- Problem rooms: write the room and the time of day, such as "back bedroom hot after 3 pm".
"Don't know" is a valid answer. It tells the contractor what to check, which is more useful than a guess.
Worked examples
Hypothetical houses, to show how the sheet reads. The ton figure is the budgeting rule of thumb only.
Same floor area, different houses
Say two 1,800 square foot homes. At 600 square feet per ton, both show "about 3 tons" on the sheet. The first, built in 1978, has single-pane windows, thin attic insulation, a big west-facing window wall and ducts in the attic. The second, built in 2015, has double-pane windows, deeper insulation and most glass facing north.
A load calculation would treat these differently even though the floor area matches. The rule of thumb cannot, which is exactly why the sheet records the other inputs and why the ton figure is for budgeting.
A hot room that is not a sizing problem
Say a back bedroom is hot every afternoon while the rest of the house is comfortable. Writing that on the sheet lets the contractor check that room's supply duct, its windows and its return path. Upsizing the whole system to fix one room usually overcools the rest of the house.
How to read what the contractors give back
Ask each contractor for a short written summary: the total cooling load in Btu/h, the equipment size chosen, and the key inputs they used. One ton equals 12,000 Btu/h, so you can convert the load into tons yourself and see how close the chosen size is.
- Sizes agree: good sign. Compare the quotes on equipment, scope and warranty instead.
- One quote is a ton larger: ask what input drove it. A clear reason, such as a vaulted room or a sunroom, is fine; "to be safe" is not.
- No load figure at all: ask for one before signing. If the contractor sized from floor area or the old unit's label, the quote is not on the same footing as the others.
What this tool does not do
The tool does not calculate a load or recommend a size. The "about X tons" line on the sheet uses a 600 square feet per ton pairing, a common budgeting rule of thumb. That is a rule of thumb for budgeting, not a sizing method; we label it as such.
It also does not check duct sizing, airflow or the equipment's rated capacity at Dallas temperatures; those are parts of a full design that the contractor handles. It does not store your sheet: close the tab and the entries are gone, so print or save it first.
What to do next
- Save the sheet as a PDF and send it ahead of each estimate visit.
- Pick the system type with the system comparison tool if you have not decided.
- Check the price range for the size the load calculation lands on in the DFW cost guide.
- Verify each contractor with the TDLR license check, and confirm the permit with the permit guide.
- Compare the quotes in the quote comparison tool, with the load figure in each column.
Sources
- City of Dallas, "Current City Code" (retrieved 2026-09-23) — verify before relying on it
- NWS Fort Worth, "1991–2020 Normals" (retrieved 2026-10-20)
- ACCA, Manual J (retrieved 2026-10-20)
Questions
Can this tool tell me what size AC I need?
No. It gathers the facts a contractor needs for a Manual J load calculation, which is what sets the size. Floor area alone misses insulation, windows, sun and ceiling height.
Why does Dallas heat matter for sizing?
DFW averages 20 days a year at or above 100 °F on the 1991–2020 normals. A system sized by rule of thumb can struggle on those days or be oversized the rest of the summer, which leaves the house clammy. A load calculation balances both.
Why do the contractors give me different sizes?
Usually because they used different inputs or none. One may have run a load calculation and another applied a square-foot rule. Ask each for the heat gain in Btu/h and the main inputs they used; the same sheet makes differences easy to trace.
Is a bigger AC better in Dallas heat?
Not automatically. An oversized system cools the air quickly and shuts off before it removes much moisture, so rooms can feel clammy, and frequent starts add wear. The right size comes from the load calculation, not from adding a ton for safety.
Do I need a new load calculation if I am replacing like for like?
It is worth asking for one. Insulation, windows and occupancy may have changed since the old unit went in, and the original may never have been sized properly. Dallas enforces a code that calls for sizing from a load calculation.
What should I do with the prep sheet?
Print it or save it as a PDF and hand it to each contractor at the estimate visit. Ask each to show their Manual J result and explain any difference from the others.
Next step
Free quote request
Get a quote to check against these numbers
- Tell us about the job. Service, ZIP, property and timing. The form says right away if your ZIP is outside the area.
- We check the license first. Requests go only to contractors whose TDLR air conditioning license we have matched on the state register. None is signed yet: if no checked contractor covers your ZIP, we email you and say so.
- Compare what comes back. Line the written quotes up in the quote-comparison tool.
No cost and no obligation. We are a publisher, not a contractor. Partner contractors will pay us for introductions; none is signed yet. How that works.
Request AC installation quotes
Free and no obligation. We pass a request on only to a contractor whose TDLR license we have checked and who covers your ZIP.