HVAC Refrigerant Charging Card
One page. Superheat, subcooling and PT for four refrigerants.
$3.99
BuyOversized vs Undersized AC
Short-cycling and humidity problems vs never reaching set point — how to tell which sizing mistake you have
The cooling load calculator is a starting estimate. This page is the symptom checklist when the equipment you already have (or were quoted) feels wrong.
What a ton means: guide. Why Manual J matters: comparison. Heating-side symptoms: furnace sizing problems. Heating ROT: furnace sizing calculator.
Re-check the ballpark tonnage before you authorize a rip-and-replace.
Open Calculator →Jump to what you need
Signs of an Oversized Unit
- Short-cycling — runs a few minutes, satisfies the thermostat, shuts off, repeats
- Humidity problems — cool but clammy; moldy smell; windows sweat
- Uneven rooms — some spaces overshoot while others never settle
- Higher bills than expected for the runtime pattern you observe
Oversizing is the classic failure mode of aggressive sq-ft-per-ton rules on tight modern homes.
HVAC
Complete HVAC Charging Guide
15 pages. Full superheat grid, PT tables, A2L safety and diagnosis.
$12.99
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HVAC Job Estimator
Quote HVAC work and catch a refrigerant mismatch before you order.
Excel or Google Sheets. Best on a computer.
$29.00
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HVAC Complete Bundle
Card, 15-page guide and the estimator workbook. All six files.
Excel or Google Sheets. Best on a computer.
$34.99
$45.98 if bought separately — save $10.99
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Cooling Comfort & Diagnosis Gear
A tonnage estimate is only a starting point. After install (or when a system misbehaves), confirm airflow and air-side split before you chase the wrong problem. These are tools already on the TestTalkHQ HVAC affiliate list.
ecobee Smart Thermostat Premium
Stable setpoints and sensor feedback help you see whether the system short-cycles or never reaches set point — classic oversize vs undersize symptoms.
View on Amazon →
BTMETER BT-100 Anemometer
Rule-of-thumb tonnage does not prove duct CFM. Measure face velocity, then convert with the duct CFM calculator.
View on Amazon →
Fieldpiece SM380V SMAN Manifold
When the air split looks wrong, verify charge with superheat/subcooling — not with square footage.
View on Amazon →
Run the Cooling Estimate
Sq ft, climate band, ceiling height, insulation quality → rough tons and BTU/hr with Manual J disclaimer.
Open Cooling Load Calculator →
Check Air-Side Delta-T
After the system is running, return-vs-supply split is a quick air-side health check.
Open Delta-T Calculator →
What a Ton Means
Why sq-ft-per-ton varies, and why this tool is not ACCA Manual J.
Read the Cooling Load Guide →As an Amazon Associate, TestTalkHQ earns from qualifying purchases.
Signs of an Undersized Unit
- Never reaches set point on design-hot afternoons
- Runs constantly for hours without satisfying the thermostat
- Hot upstairs / west rooms while the thermostat location looks OK
- Delta-T may look “normal” while the house still cannot reject the load
How to Tell Which
- Watch cycle length on a hot afternoon with a clean filter.
- Measure return-vs-supply split: delta-T calculator.
- Confirm airflow and static before blaming charge or tonnage.
- Compare nameplate tons to a Manual J — not only to a sq-ft rule.
FAQ
Can low refrigerant look like undersizing?
Yes. Charge diagnostics belong on gauges: superheat / subcooling.
Should I upsize to “fix” humidity?
Usually the opposite — oversized equipment often worsens humidity by short-cycling. Fix runtime and latent removal with correct sizing and airflow.