In Permanent Load Reduction Plan Case Study #1, we revealed what I call the Hidden Comfort Thief — building defects quietly stealing HVAC performance.
But once you know the thief exists, the next step is the hunt.
This Permanent Load Reduction Plan Case Study #2 focuses on the investigation phase. Instead of assuming the HVAC system was the problem, we tracked where the load was actually coming from.
This type of investigation aligns with Home Performance diagnostics, where the house is treated as a system rather than focusing only on HVAC equipment.
The trail quickly led to the attic.
There we discovered two issues working together to increase system demand:
- attic duct leakage
- uncontrolled air infiltration
These hidden problems were forcing the HVAC system to work far harder than the design intended.
Key Findings From Permanent Load Reduction Plan Case Study #2
During the investigation phase of this Permanent Load Reduction Plan, two major sources of hidden load were identified.
Primary Load Drivers
- attic duct leakage allowing conditioned air to escape into the attic
- air infiltration pathways pulling outdoor air into the building
- increased heating and cooling loads caused by the interaction of these two issues
- reduced HVAC system effectiveness because conditioned air never reached the living space
These findings are common in Home Performance assessments, but the Permanent Load Reduction Plan approach translates these discoveries directly into measurable load reduction.
The Homeowner Complaint
Like many homes that eventually require a Permanent Load Reduction Plan, the homeowner reported classic comfort problems:
- uneven room temperatures
- HVAC system running longer than expected
- difficulty maintaining temperature during extreme weather
These symptoms often lead homeowners to believe the HVAC system needs replacement.
However, Permanent Load Reduction investigations start with the building.
The Investigation: Hunting the Load
During the inspection, attention quickly shifted to the attic.
In both Home Performance investigations and Permanent Load Reduction Plan assessments, the attic is one of the most common locations where hidden loads originate.
This is where the duct system and building envelope intersect.
The inspection revealed two critical defects.
Attic Duct Leakage
Supply ducts were leaking conditioned air directly into the attic
and crawlspace.
When this happens, the system is effectively heating or cooling the attic rather than the living space.
This reduces delivered airflow while increasing system load.
https://www.energy.gov/energysaver/minimizing-energy-losses-ducts
Air Infiltration Pathways
The building envelope also allowed outside air to enter through several attic bypasses, including:
- attic top plates
- wiring penetrations
- plumbing penetrations
- recessed lighting
- attic access points
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.energystar.gov/ia/home_improvement/home_sealing/AirSealingFS_2005.pdf
Together, these defects created a cycle where conditioned air escaped while outside air was continuously pulled into the home.
Load Reduction Results
The goal of a Permanent Load Reduction Plan is not simply identifying defects — it is quantifying how much load those defects create.
Initial blower door testing measured:
9,471 CFM50 (27 ACH50)
After modeling improvements including air sealing and duct leakage reduction:
Projected infiltration dropped to 5,953 CFM50
Heating Load Reduction
Before PLR Plan
| Area | Heating Load |
|---|---|
| 1st Floor + Basement | 92,354 BTUh |
| 2nd Floor | 70,462 BTUh |
| Total | 162,816 BTUh |
After PLR Plan
| Area | Heating Load |
|---|---|
| 1st Floor + Basement | 73,376 BTUh |
| 2nd Floor | 46,006 BTUh |
| Total | 119,382 BTUh |
Heating Load Reduction
162,816 BTUh → 119,382 BTUh
Total Reduction
43,434 BTUh
≈ 27% reduction in heating load
Cooling Load Reduction
Before PLR Plan
| Area | Cooling Load |
|---|---|
| 1st Floor + Basement | 38,365 BTUh |
| 2nd Floor | 51,995 BTUh |
| Total | 90,360 BTUh |
After PLR Plan
| Area | Cooling Load |
|---|---|
| 1st Floor + Basement | 35,842 BTUh |
| 2nd Floor | 33,770 BTUh |
| Total | 69,612 BTUh |
Cooling Load Reduction
90,360 BTUh → 69,612 BTUh
Total Reduction
20,748 BTUh
≈ 23% reduction in cooling load
Where the Load Was Coming From
The Manual J load breakdown revealed the real drivers behind the system demand.
First Floor Heating Load Breakdown
| Source | BTUh |
|---|---|
| Walls | 10,429 |
| Windows | 6,402 |
| Doors | 1,728 |
| Ceiling | 6,010 |
| Floors | 4,955 |
| Air Infiltration | 50,208 |
| Duct Losses | 12,621 |
Air infiltration alone accounted for over half of the heating load.
Second Floor Cooling Load Breakdown
| Source | BTUh |
|---|---|
| Windows | 17,949 |
| Walls | 2,443 |
| Ceiling | 2,633 |
| Floors | 5,785 |
| Infiltration Sensible | 1,866 |
| Infiltration Latent | 5,260 |
| Duct Losses | 16,059 |
Duct losses created more than 16,000 BTUh of cooling load.
Why Permanent Load Reduction Should Come Before HVAC Replacement
One of the biggest mistakes in residential HVAC projects is replacing equipment before understanding the building load.
When infiltration and duct leakage increase system demand:
- systems appear undersized
- contractors install larger equipment
- comfort problems continue
A Permanent Load Reduction Plan reverses that process.
Instead of sizing equipment to overcome building defects, the defects themselves are corrected.
This reduces the load placed on the HVAC system permanently.
Permanent Load Reduction Case Study Lesson
This case study reinforces a core principle:
Most HVAC problems are actually building problems.
In this home:
- severe air infiltration drove heating demand
- attic duct leakage drove cooling losses
- correcting those issues reduced load by more than 40,000 BTUh
This is the goal of a Permanent Load Reduction Plan — reducing the loads that force HVAC systems to work harder than necessary.
Video Case Study
This video walks through Permanent Load Reduction Plan Case Study #2 and documents the investigation phase—what we call the hunt for attic load driver
