HVAC Troubleshooting - AC Performance Measurement

Impact: Very High

Phase 1: Measure Temperature Drop (Supply vs. Return)

Is the AC coil producing enough cooling? Tools needed: Two digital thermometers (~$20–40)

What to look for: 16–22°F difference = good | Under 15°F = investigate | Over 23°F = airflow too low

Measurement steps:

Measure return air temp at large grille nearest furnace

Measure supply air temp at first vent from furnace

Calculate difference: Return Temp – Supply Temp

Recording measurements:

Morning Reading

—

Afternoon (5 PM)

—

Evening Reading

—

Differences automatically calculated as you enter data

Impact: Very High

Phase 2: Map Airflow at Every Vent

Tools: Vane anemometer (~$30–50)

What you're looking for: Large differences (e.g., 450 ft/min in one room, 80 ft/min in another) indicate balancing or duct issues.

Measurement steps:

Go to every vent/register in the home

Measure air speed (ft/min) with anemometer

Record room name and reading

Identify rooms with significantly lower/higher airflow

Record airflow readings:

Room	Air Speed (ft/min)	Notes

Impact: Very High

Phase 3: Measure Temperature by Room

On a hot day (5–6 PM), record room temps and compare to supply air temp at each register.

Key insight: If all registers supply 58–60°F but some rooms are still hot, the problem is airflow or heat gain, not the AC coil.

Measurement steps:

Record room temperature at each major room

Measure supply air temp at register in each room

Compare readings to identify problem areas

Record room temperatures:

Room	Room Temp (°F)	Supply Temp (°F)	Notes

Impact: Very High

Phase 4: Evaluate Heat Gain Sources

Tools: Infrared thermometer (~$25)

Example readings: Door 108°F, Adjacent wall 96°F, Interior wall 77°F → Door is major heat source.

What to measure:

Interior wall surface temperature (west-facing)

Ceiling temperature (especially west/south side)

Door surface temperature (metal/exterior)

Window glass temperature

Floor near windows/doors

Record heat gain readings:

West-Facing Door Surface

West-Facing Wall (interior)

Ceiling Temperature

Window Glass Temperature

Impact: High

Attic Inspection Checklist

Best done on a cool morning. Bring a ruler for measuring insulation depth.

Insulation checks:

Measure insulation depth (target: 16–20 inches for R-49 to R-60)

Check for dark, compressed insulation (poor effectiveness)

Identify bare drywall areas (missing insulation)

Check for insulation blown away from soffits (wind washing)

Identify wiring penetrations

Identify plumbing penetrations

Check attic hatch for gaps and poor sealing

Impact: Very High

Furnace Measurements (Technician)

Have an HVAC technician measure these critical parameters.

Required measurements:

Total External Static Pressure (TESP)

Return static pressure

Supply static pressure

Delivered airflow (CFM)

Record measurements:

Total External Static Pressure (TESP, in. H2O)

Delivered Airflow (CFM)

Impact: High

Filter Experiment (Easy & Inexpensive)

If high static pressure found: Test airflow with different filter types.

Warning: Only test without filter briefly! Never run system filter-less for extended periods.

Test procedure:

Install MERV 11–13 filter (upgrade from current)

Measure vent airflow (ft/min)

Measure supply/return temp difference

Note time to cool house (if improvement observed)

Comparison results:

Current Filter

Current Airflow (ft/min)

New Airflow (ft/min)

Impact: Moderate

Outdoor Unit Visual Inspection

Simple indicators that refrigeration cycle is operating normally.

What to check (with AC running):

Large copper line is cold and sweating (condensation)

Small copper line is warm

Outdoor fan is running and producing strong upward air flow

Condenser fins are clean (no dust/debris blockage)

Impact: High

Window & Door Solar Orientation Survey

Identify which windows receive direct afternoon sun.

Survey steps:

Draw simple floor plan of home

Mark orientation of each major window (N/S/E/W)

Identify which windows get afternoon sun (3–7 PM)

Note glass area of west-facing windows/doors

Identify opportunities for shading (awnings, shutters, film)

AC Performance Troubleshooting Guide

Measurement steps:

Recording measurements:

Measurement steps:

Record airflow readings:

Measurement steps:

Record room temperatures:

What to measure:

Record heat gain readings:

Insulation checks:

Required measurements:

Record measurements:

Test procedure:

Comparison results:

What to check (with AC running):

Survey steps: