Calculation method
Ask whether the proposed capacity is supported by a home-specific Manual J calculation, and identify the method or software used.
Phoenix HVAC sizing evidence
Does the quoted HVAC capacity have a home-specific load calculation behind it?
A capacity number is easier to compare when the proposal shows what home facts and design conditions support it. Use the quote to separate the load calculation from the later equipment choice.
General information only · Not a load calculation, equipment-sizing, engineering, or code opinion
Keep the decisions separate
Load calculation first. Equipment selection second.
ACCA describes Manual J as its residential load-calculation standard. A quote review can verify whether a home-specific calculation is documented and whether the proposed capacity is connected to it; it cannot recreate or certify the calculation.
Home inputs
Record the measurements and envelope assumptions used, including windows, insulation, orientation, infiltration, and other relevant property facts.
Design conditions
Ask for the indoor and outdoor design conditions and both sensible and latent cooling loads shown in the output.
Calculation scope
Clarify whether the work is a whole-home block load or room-by-room calculation and what parts of the home were included.
Equipment selection
Keep the load result separate from the later equipment-selection decision. The quote should explain how proposed capacity follows from the calculation.
Quote fields
Ask for the evidence that makes capacity comparable.
A complete response can use the contractor's own format, but it should resolve these decision fields.
| Field | Decision-ready answer | Reason to clarify |
|---|---|---|
| Method | Calculation method or software and date | Only square footage or old tonnage is cited |
| Property inputs | Measurements and relevant envelope assumptions | Generic or unknown assumptions |
| Conditions and loads | Design conditions plus sensible and latent loads | Only a final tonnage appears |
| Scope | Block or room-by-room and included areas | The calculation boundary is unclear |
| Selection basis | How the proposed capacity and later model selection use the result | The output and equipment do not connect |
Read the result
Clarify, verify, or compare.
No home-specific evidence is named.
Ask what method, inputs, and design conditions support the capacity.
A calculation exists but the bridge is incomplete.
Reconcile the output with the proposed capacity and model-selection basis.
Both proposals document their sizing basis.
Compare assumptions and differences before treating either tonnage as equivalent.
Primary sources
Use the standard owner's guidance.
ACCA Manual J
ACCA's residential load-calculation standard and technical overview.
ACCA Manual J Residential Load Calculation ↗ACCA homeowner guidance
Homeowner-oriented context for quality HVAC design and installation.
ACCA Homeowner Guidance ↗Sources reviewed August 25, 2026. Confirm project-specific calculations and commitments with the responsible licensed contractor.
Common questions
Know what the calculation can—and cannot—settle.
Is replacing the old unit with the same tonnage enough?+
Existing tonnage is a useful fact, but it is not a home-specific load calculation. Ask what current property inputs support keeping or changing that capacity.
Does Manual J select the exact model number?+
No. Manual J estimates heating and cooling loads. Equipment selection is a later step, commonly associated with Manual S, that considers the load and the performance of a specific system.
Should the contractor provide the calculation output?+
Ask for enough written output to understand the inputs, design conditions, calculated loads, and connection to the proposed capacity. The contractor can explain the form and level of detail it supplies.
Already holding a written quote?
Make the sizing basis part of the market bar.
SecondLook preserves the capacity and documented sizing assumptions before comparing a lower option.
- No deposit
- No contractor visit without your approval
- 15% of verified savings only if you use a lower comparable option