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Duct Leakage TestingPaul W. Francisco, University of Illinois

Why Test?

• Many duct locations are unpleasant

• Many duct systems do not leak very much

• Those that do can cost a lot of energy

• 10% supply leak corresponds to about 15-20% energy

penalty



What is the question?

• Are the ducts tight enough for certification (e.g. HERS,

Energy Star)?

• Should air sealing be done by a program (e.g. utility,

weatherization)?

• Where are the leaks?

• Has enough sealing been done?

• How much did we save?



Very Important…

How often does the test give the

correct feedback?

Duct Leakage Diagnostics

• Pressure Pans

• Duct Blaster

• Delta-Q

Duct Leakage Diagnostics

•What test should be used?

• When should that test be used?

• Why should that test be used?



Test Comparison

AccessRegisters

Automation Leakage tooutside

TotalLeakage

Leakage atOperating

Conditions

Pressure

Pan √ √

Duct Blaster √ √ √

Delta-Q √ √ √

Nulling Test for Comparison

• Use a Duct Blaster as envelope fan to “null out” change in

envelope pressure caused by unbalanced duct leakage

• First with normal operation – unbalanced leakage

• Second with return isolated and a Duct Blaster assisting the

AH fan so there is no return leakage – supply leakage

• Difference is return leakage

• Measures leakage directly – thought to be accurate

• Very sensitive to wind

Nulling Test

-500

-400

-300

-200

-100

0

10:41:30 10:42:00 10:42:30 10:43:00 10:43:30 10:44:00 10:44:30 10:45:00 10:45:30 10:46:00 10:46:30 10:47:00 10:47:30 10:48:00 10:48:30 10:49:00 10:49:30

PoutBD Ps upplen Pnull



Nulling Test

- 1

- . 5

0

. 5

1

0 20 40 60 80(mean) meanqenv

95% CI Fitted values

Site 4 Unbalanced

Pressure Pan Test

• Essentially a zone pressure diagnostic for the ducts

• Depressurize house with blower door

• Cover registers, one at a time, with pressure pan andmeasure pressure

• Elevated readings indicate holes in the ducts that areconnected to outdoors

Pressure Pan Test

• Simple to do

• Need to access all registers

• Identifies specific duct runs that have problems

• Robust/Repeatable



Pressure Pan Test

• Proximity of holes to register impacts reading – closer means higher

• Implication – LOW pressure leaks give HIGHER pressure

pan readings

• Does not indicate actual flow leakage

• Rewards most for leaks that matter least

Pressure Pan Test Example #1

• 8 registers: 2 3 4 3 4 2 3 2

• Two possibilities:

• Modest leaks at boots

• Larger leak at plenum

• Boot leaks are not worth sealing, plenum leak is!

Pressure Pan Test Example #2

• 8 registers: 2 3 4 18 4 2 3 2

• Register 4 has a major leak

• May also be responsible for magnitude of other readings



Pressure Pan Test – other considerations

• Many can’t be covered by a pressure pan – use anythingthat can fully cover the register/grille, e.g.

• Duct mask tape

• Sweatshirt

• Pillow

Pressure Pan Test – other considerations

• Some ducts lead to registers through each side of a wall

• Seal one off

• Pressure pan the other one

• Failure to seal one off is like leaving half of the register

uncovered

Duct Blaster Test

• Leakage to Outside?

• Seal all registers

• Pressurize house with blower door

• Pressurize ducts with Duct Blaster

until duct-to-house pressure is zero

• Duct Blaster flow is leakage number



Duct Blaster Test

• More difficult to do than pressure pan• Sealing registers can be time-consuming

• Registers may be inaccessible

• For energy concerns, supply is moreimportant

• To assess supply and return separately,need to isolate the two sides and testthem individually

Duct Blaster Test

• Also does not indicate actual leakage

• Is actually a measure of airtightness

• Counts holes equally regardless of location

• Robust/Repeatable*

* If leakage to inside is low – see next slide

Effect of Interior Leakage and Imprecise House-Duct Pressure Balance

Source: Pigg and Francisco 2008

0

5 0

1 0 0

1 5 0

2 0 0

S u p p l y C F M @ 2

5 E r r o r R e l a t i v e t o

E x a c t M a t c h i n g

0 500 1000 1500Total Supply Leakage, CFM @ 25

0.2 Pa mismatch

0.5 Pa mismatch

1.0 Pa mismatch



Duct Blaster Test

• Total leakage?

• Don’t need blower door

• Includes leakage to inside – not focused on energy

concerns

• If low total leakage, then certainly low leakage to outside

Delta-Q Test

• Preferably automated

• Do 4 multi-point blower door tests

• Depressurization, air handler off

• Depressurization, air handler on

• Pressurization, air handler off

• Pressurization, air handler on

• Use software to calculate leakage estimates from flow

differences

Delta-Q Test

• Estimates actual leakage

• Requires only a blower door (and a computer)

• Do not need to access registers

• Leakage to outside only



Delta-Q – “When Last We Met”

• Completed field study performed in conjunction withMidwest weatherization agencies

• Looked at:

• Ramping sampling protocol

• Analysis methods – non-negative least squares (NNLS) and

“scanning”

• Bin size for data processing

• Possibility of using one ring instead of two

Delta-Q – “When Last We Met”

• Conclusions

• NNLS and scanning gave similar results, NNLS ok

• NNLS since dropped for variety of reasons

• Bin size of 5 Pa good, 1 Pa too small

• Possibility of using one ring instead of two was promising,

but not conclusive and needed protocol for choosing ring

• Wind was a significant problem

• How to best minimize impacts

Since then…

• Study on new Wisconsin homes completed (funding Focus

on Energy)

• 19 homes, most for Energy Star or EPACT

• User repeatability experiment conducted (C. Olson)

• 7 homes by volunteers

• Follow-up study in Illinois (funding DOE and ODOD)

• 14 homes with ducts outside conditioned space



Follow-up Project (concluded March 2009)

• Various options for testing

• Ramping vs. stations

• Two rings vs. one ring

• Feasibility / protocol

• Location of outdoor pressure hose

• To reduce wind noise

• How to put a number on uncertainty?

Field Study

• 14 homes

• Chosen to have ducts outside conditioned space

• Average 1816 ft2 (range 1144 – 3332)

• Average 10.6 ACH50 (range 6.7 – 15.6)

Tests Performed

• At least 5 repeats of each of ramping and stations

• Also 1-3 one-ring, two-ramp tests per home• “Control” tests done when time permitted

• Duct Blaster and pressure pans

• Nulling



Ramping vs. Stations


• Collect data in 5 Pa bins

• Difference between AH on and

AH off

• Software calculates leakage

estimates from best fit –

“scanning”

Delta-Q Accuracy – Wisconsin project



Ramping Accuracy – follow-up project


• Stations provided estimates slightly higher than ramping on

average, about 10 cfm on both supply and return

• Stations takes longer under windy conditions

• Stations more sensitive to sampling rate

- 5 0

0

5 0

1 0 0

1 5 0

D i f f e r e n c e b e t w e e n F u l l a n d R e d u c e d S a m p l i n g , c f m

Ramping, Supply

Ramping Return

Stations, Supply

Stations, Return





CONCLUSION

Prefer Ramping

Outdoor Pressure Location

• Three options considered

• Leeward side (expected best)

• 4-side manifold

• Blower door side (sometimes

same as leeward)

• Question: Do you get enough

benefit by running additional

hoses?


- 2 0 0

0

2 0 0

4 0 0

6 0 0

R a m p i n g - S u p p l y E s t i m a t e s , c f m

0 100 200 300 400Nulling Test Supply Leakage, cfm

one-one l ine Leeward

Manifold Blower Door




0

2 0

4 0

6 0

8 0

1 0

0

S t d . D e v . o f S u p p l y L e a k a g e E s t i m a t e s , c f m

LeewardManifold

Blower Door

Outdoor Pressure Location - Leeward

- 4 0 0 0

- 2 0 0 0

0

2 0 0 0

4 0 0 0

B l o w e r D o o r F l o w , c f m

-50 0 50Leeward Pressure, Pa

AH off

AH on


CONCLUSION

Blower Door Side



One-Ring vs. Two-Ring

• If one ring was used, choose smallest ring that gets to 30Pa

• One ring tests with only one ramp extracted from normal

test data

• One ring tests with two ramps done as additional tests –

usually only one per house


1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

A v e r a g e O n e - R i n g S u p p l y E s t i m a t e , c f m

0 100 200 300 400 500Average Two-Ring Supply Estimate, cfm


0

2 0

4 0

6 0

8 0

S t a n d a r d D e v i a t i o n o f L e a k a g e E s t i m

a t e , c f m

S up pl y, t wo ri ng s R et ur n, tw o ri ngs

Supply, one ring Return, one ring




• No statistical difference between one-ring and two-ring testaverages

• Primary benefit of two-ring tests is additional data from two

ramps

• When conditions warrant can do two ramps for a single ring

One Ring vs. Two Rings

CONCLUSION

Can Use One RingUse Smallest Ring that gets to 30 Pa

Use Two Ramps unless calm winds

Uncertainty Estimation for Delta-Q

• Would allow user to determine whether leakage estimate

could be relied upon

• Use variability among repeated tests compared to

individual Delta-Q test data standard error to obtain

multiplier (to standard error) that covers 95% of estimates

• Wisconsin, user repeatability experiment, and Illinois

studies all suggested multiplier between 2 and 3

• Suggest use about 2.5



Delta-Q Final Recommendations

• Ramping protocol

• Outdoor reference on blower door side of house

• One ring

• Smallest that can reach 30 Pa

• Two ramps unless calm conditions

• Use uncertainty estimate to be built into software

Comparisons to Other Tests

• Duct Blaster test at 25 Pa

• Pressure Pan

• Mean value for Wisconsin

• Mean and median values for Illinois

Comparison to Duct Blaster – Wisconsin project



Comparison to Duct Blaster – follow-up project

Comparison to Pressure Pan – Wisconsin study

Comparison to Pressure Pan – follow-up study



Comparison to Other Tests – Conclusions

• All tests show very low leakage or very high leakage

• Duct Blaster

• Tends to overestimate – leakage pressures lower than 25 Pa

• Pressure Pan

• Median tracks leakage reasonably well with regard to

indicating appropriateness of air sealing

Comparison to Other Tests – Conclusions

• Duct Blaster

• Most appropriate for new construction when ducts should be

tight in the first place

• Best done at rough-in when ducts are still easily accessible

• Pressure Pan

• Use median to indicate value of air sealing (suggest 4 Pa)

• Individual readings can highlight specific defects

Conclusions

• No one test appropriate for all conditions

•Use each as needed

• Delta-Q can be useful for weatherization

• Low or high leakage estimates often conclusive, simple test

• Pay attention to uncertainty!

• Pressure pan can also be useful

• Median for overall leakage assessment

• Individual readings to highlight major problems



Test Usage

• Can be used as screening tools for each other

• Do pressure pan, if sealing needed can do Delta-Q to get

leakage estimate for program-wide savings estimate

• Do Delta-Q (gets blower door CFM50 also), if indicates

possible need for sealing do pressure pan to target leakage

location