Multi-Family Case Studies
"The Proof is in the Pudding!"
A few of the following properties have participated in their local utility's multi-family rebate program that focuses on using building science principles by using high performance diagnostic equipment to measure and verify existing and improved conditions. This equipment (Blower Door and Duct Blaster) measures initial CFM loss and post CFM improvements, (CFM stands for Cubic Feet per Minute of Air Flow). A few of the following communities also participated in a grant program partially funded by the Department of Energy (DOE) that focused on comprehensive energy efficiency measures in partnership with their local utility's Multi-Family Program. The data reflects comprehensive duct sealing and thermal boundary air sealing improvements, mostly verified by a 3rd party RESNET rater. "Kudos" to your local utility company that recognize the importance of measuring and verifying proper air sealing techniques in reducing CFM loss!
ACH50 stands for Air Changes per Hour at 50 Pascals with the Blower Door. We do not get ACH50 in multi-family too tight, or below 5 ACH50. We also try to achieve between .35 and .45 ACHn (natural air changes per hour) at test-out. We also strive to achieve ACH50 test-out between 5 to 8 ACH50, which is ideal for an apartment in our climate zone. This is dependent on the agreed upon work scope, age of the community, construction, sizing of the mechanical components, gas appliances, etc...as we do not want an apartment too tight to where mechanical ventilation is needed.
Congratulations !
Joseph on Huebner
San Antonio
Click Here to see the Final Air Test Report with Blower Door
Pre Test
Conditioned Square Footage=846
Average Ceiling Height=8
Total House Volume=6,768
CFM at -50 Pa Pressure=1424
CFM50 * 60 / Volume=12.62411348
n = 20 * H * S * L=19.2
ACH50 / n=0.6575059102
ACHn=0.66
ACHn
Post Test
Conditioned Square Footage=846
Average Ceiling Height=8
Total House Volume=6,768
CFM at -50 Pa Pressure=1070
CFM50 * 60 / Volume=9.485815603
n = 20 * H * S * L=19.2
ACH50 / n=0.494052896
ACHn=0.49
BLOWER DOOR - AIR SEALING with Test In/Test Out
Square Footage: 162,496
Year Built: 1983
# of Units: 192
Avg apartment size - 846 sq. ft.
Work Scope: Seal upflow return air if needed, new jamb up front door weatherstripping, seal registers, seal penetrations. and any other holes/leaks inside the thermal boundary.
This work scope recaptured 354 CFM loss per apartment! Or, we reduced the previous loss by 25% We far exceeded the utilities goal of a 10% reduction in CFM loss!
Blower Door Test-In Avg ACH50 Leakage = 1,424 CFM
Blower Door Test-Out Avg ACH50 Leakage = 1,070 CFM
The ACHn came in at a respectable .49 ACHn.
We could have sealed the thermal boundary tighter through the duct system, other measures, etc... but the work scope did not provide for such a measure. The ACH50 came in at 9.48, a bit higher than the 5 to 8 ACH50 that we like to achieve in multi-family dependent on construction, work scope and other factors.
NOTE: On the top floor units, a few months later, we did replace the grey flex duct work and added R30 insulation. Therefore, the ACH numbers will be lower with much improved energy efficiency and comfort!
Town Lake - Austin
Measures: Furrdown Duct Seal*, Attic Insulation, Tune Up "On Steroids", Honeywell Lyric T6 Smart Thermostats, Water Saving Devices
Square Footage: 239,264
Year Built: 1995
Number of Units: 256
Total Projected kW Savings: 343.58
Total Projected kWh Savings: 836,611
* Note: The furrdown furnace/air handler unit is generally located above your shower or above your washer and dryer.
These results are very typical to the importance of furrdown duct seal and it's significant contribution ranging from 64% to 80% to overall kW and kWh savings to any given Mulit-Family community!
The local utility projected kW savings of 343.58 and kWh savings of 836,611 at the conclusion of the project in the Spring of 2025. The furrdown duct seal measure portion contributes 65% of total kW savings and 54% of total kWh savings!
Furrdown Duct Seal
kW Savings 223.15
kWh Savings 450,042
Smart Thermostats
kW Savings 21.95
kWh Savings 125,752
Insulation
kW Savings 57.26
kWH Savings 27,321
Water Saving Devices
kW Savings 10.74
kWh Savings 114,929
HVAC Tune Ups
kW Savings 30.48
kWh Savings 118,566
"The Math" each measure as a % to total kW Savings
Furrrdown Duct Seal 64.95%
Insulation 16.67%
Tune Ups 8.87%
Thermostats 6.39%
Water Saving Devices 3.13%
South Congress Commons
Square Footage: 41,099
Year Built: 1979
# of Units: 68
Test-In Avg Total Duct Leakage: 500 CFM = 63% leakage
Test-Out Avg Total Duct Leakage: 38 CFM = 5% leakage
Test-In Avg Duct Leakage To Outside: 338 CFM = 42% leakage
Test-Out Avg Duct Leakage To Outside: 24 CFM = 3% leakage
Blower Door
Test-In Avg ACH: 11
Test-Out Avg ACH: 6
Austin Gardens
Square Footage: 75,000
Year Built: 1979
# of Units: 150
Test-In Avg Total Duct Leakage: 334 CFM = 55% leakage
Test-Out Avg Total Duct Leakage: 78 CFM = 12% leakage
Test-In Avg Duct Leakage To Outside: 199 CFM = 31% leakage
Test-Out Avg Duct Leakage To Outside: 57 CFM = 9% leakage
Blower Door
Test-In Avg ACH: 14
Test-Out Avg ACH: 7
Since 2018, it is estimated that we have......
SAVED kW- 20,443.00
SAVED kWh- 60,878,880.00
Whisper Hollow
Square Footage: 150,160
Year Built: 1983
# of Units: 220
Test-In Avg Total Duct Leakage: 348 CFM = 41% leakage
Test-Out Avg Total Duct Leakage: 46 CFM = 6% leakage
Test-In Avg Duct Leakage To Outside: 254 CFM = 30% leakage
Test-Out Avg Duct Leakage To Outside: 27 CFM = 3% leakage
Blower Door
Test-In Avg ACH: 11
Test-Out Avg ACH: 8
The Enclave
Square Footage: 48,842
Year Built: 1982
# of Units: 90
Test-In Avg Total Duct Leakage: 171 CFM = 28% leakage
Test-Out Avg Total Duct Leakage: 50 CFM = 8% leakage
Test-In Avg Duct Leakage To Outside: 107 CFM = 18% leakage
Test-Out Avg Duct Leakage To Outside: 28 CFM = 5% leakage
Blower Door
Test-In Avg ACH: 10
Test-Out Avg ACH: 8