Concerning duct testing in crawlspaces (this is for new houses for Energy Star, but will be the same for existing houses):

I have a house on a conditioned crawl with ducts in that crawl.  There is an exterior hatchway into the crawl, and no intentional connection between the house and the crawl.  When performing a total duct leakage test, no problem, just open the hatch before the test.  When performing a duct leakage to outside test, the crawlspace ducts never experience the effect of the blower door, so the test is inaccurate, with leakage to outside numbers that are too high.

We know the numbers are too high in a case like this, and we have been able to simulate the problem in a house with a basement by taping the basement door while doing the leakage to outside test.  Just today, we tested 2 identical houses that we had sealed while under construction.  The 2 identical houses - 1400 ft2 on a basement making them 2800 ft2 of conditioned space - had building leakage of 620 CFM50 and 650 CFM 50.  Duct systems are entirely within the shell.  Both had a leakage to outside numbers of 20 and 26 CFM25 range.  We then taped the doors to the basements and got numbers of 82 and 92 CFM25 as leakage to the outside.  In these cases, off by a large factor from the real 20-25 number.

Without cutting a hole in the floor or installing a second blower door in the crawlspace, do you have any ideas?

Ed Minch

Tags: conditioned, crawl, duct, testing

Views: 923

Reply to This

Replies to This Discussion

Ed, if you have a conditioned crawler you are implying conditioned air to that area.  Why then would you care about leakage to the outside? If, however you are saying that what you have is a thermal boundary (only) there and you want to quantify the leakage to that area you could pressurize the crawl space, and equalize that pressure in the ducts.  This would give you leakage to the house.  You could then subtract that amount of CFM from total leakage.  Just a thought.


Energy Star V 3.0 requires a duct leakage to outside AND a total duct leakage test - the code (2009 + 2012 IECC) says test only if ducts are outside.  So for Energy Star we are testing all systems whether or not they are inside, with exceptions for very tight houses.  So the question is, how would you do the test without cutting a hole between the house and the crawl or installing another blower door in the crawl.


Ed Minch 

Ok, I must be missing something here or my memory is going - if the crawl is part of the conditioned space & all the duct runs are visible, no test is required if memory serves me correctly or did I possibly miss an update somewhere?

Next for a crawl to be conditioned / sealed it should have a vent running in there which should be sealed

As for still doing a leakage to the outside test, seeing the crawl is now considered part of the inside, you only have to worry about setting up the blower door in one exterior doorway & making sure all the other ones - including the crawl sace door are closed while any interior doors are opened.

No matter what you do, you will always have a CFM figure as the duct testers we use need so much to maintain the pressure past the fan


As I mentioned, the new Energy Star 3.0 requires BOTH a total duct leakage and leakage to outside test (not the code - 2009 IECC for new homes). However, the code states in its definition of Conditioned Space, that any space with an uninsulated duct is considered conditioned - it does not have to have an register.  So if the crawl space in question is conditioned (maybe a register, maybe not) but there is no connection to the interior of the house above, how do I get an accurate leakage to outside test?  As I mentioned, I can only think of 2 ways to do it - cutting a hole between the house and the crawl or installing another blower door in the crawl.  I don;t want to do either of those.  So my question was, can anyone think of anther way to do the test?

Ed Minch

If you really don't want to get a second blower door, get a length of flex duct and rig up a shunt from a window to the crawl space door.... cardboard panels, lots of tape, etc. 

You have an interesting scenario there.  I'm wondering how the ducts you're working with can meet the requirement of being within the pressure boundary of the home?  If there is no direct connection between the crawler and the living space I would say they aren't.  Maybe I'm over looking something.


I have found this disconnect before - between existing home "standards" and what the building codes say.  We have worked in both existing homes doing instrumented audits since 1981, and in new homes air sealing and testing then delivering certifications since 1982, so are familiar with both scenarios and we take the best of each world and applyit to the other.  We find that the recent retrofit standards don't match the new home building codes in many areas, and those trained in one area are not often conversant in the other.

I was not thinking I was going to get questions along these lines when I posed the problem and am surprised that I am.  So translating this into a retrofit scenario, if you had a house with a heater and ductwork in the crawl space, but that crawl space only had an exterior hatch with no connection to the house, what would you do? Where would the envelope be and under what circumstances would you test the ducts?

And thanks to David - that is a solution we will think about - lack of blower doors is not the issue, but a solution that we can imrovise quickly IS -  quick equals affordable.

Ed Minch

Bear with me here while I lay out some background that should clarify the field-testing decision Ed has presented.  I, too, have struggled with this scenario.

I think part of the problem is conflicting definitions.  In the new construction ENERGY STAR context, you have to consider both the IECC 2009 definition Ed cited for Conditioned Space, and also the RESNET definition (see Appendix A page A-2 of the RESNET Standard).  Under the RESNET definition, Ed's crawlspace is "Conditioned, indirectly", and not the same as a "Conditioned, directly" crawlspace, which is held at the thermostat setpoint.

Going a step farther, if you model this crawlspace in REM/Rate, it is best modeled as an "Enclosed Crawlspace" rather than a "Conditioned Crawlspace"  -- because in REM, a "conditioned" space is held the to the thermostat setpoint, while the temperature in other crawlspaces is calculated iteratively as part of the energy analysis.

Why make these points?  Because when I consider all these details, I consider Ed's crawlspace to be outside of the primary air and thermal barriers.  If that is the case, then the problem of somehow depressurizing the externally-accessed crawlspace goes away.  No cardboard-&-tape improvisation necessary!


Sorry for the delay.  There are 2 problems with your scenario.  First is that, in RemRate 12.96, if I call the crawlspace enclosed, then I have to insulate the ceiling of the crawl and insulate the ducts (for code and, therefore, EStar) and plumbing pipes for RESENT. Insulating these 3 items is much more expensive than insulating the walls of the crawlspace.  I can open a small duct in the crawlspace (we install a 5" for every 750 ft2) to satisfy RESENT. 

Second is that the HERS index goes up (gets worse) by either 2 or 3 points in the 2 houses I tried.  Many of my builders are now starting to market the HERS index, and the difference between a (say) 64 and 66 means something to them.

So "enclosing" the crawlspace costs more to build, and will result in a higher HERS index, forcing perhaps additional cost to make up the points to get to EStar or to a marketable number.  So I don't want to do this.

Which leaves me with my original question - how do I test duct leakage to the outside if the conditioned crawlspace is not connected to the house?

Thanks for the reply

Ed Minch

Hi Ed,

Enclosed crawlspaces can be modeled in REM without floor insulation;  indeed, one of the building files I created for testing REM's implementation of ESv3.0 has an enclosed crawl with no floor insulation, only crawl wall insulation -- and it passes ESv3.0, IECC2009, and all RESNET requirements.  The crawlspace in it is nothing special -- it looks just like many of the unvented crawlspaces I visited while doing HERS ratings in the mid-2000's.  It can even have a supply register and return path, as required by many building codes when the crawl is sealed from outside.

If the crawlspace temperature does not track the thermostat closely, it should not be modeled as a conditioned crawl.  Considering it a conditioned crawl for the sake of a better HERS Index is a slippery slope.  I'd recommend using your own expertise along with the modeling results of different scenarios to guide your builders to make different decisions.  An externally accessed crawlspace is very likely a leaky crawlspace -- not a good place for a supply register.  I still say the most representative measurement of duct leakage to outdoors will exclude this crawlspace from conditioned space.

Best wishes,

Brian Christensen



Thanks for the input - we will consider.

Ed Minch

It does, but even though:

"According to the RESNET Formal Interpretation mentioned above: The measured outside leakage shall be deemed to be 0  CFM25 for each system the meets the following criteria: 100% of ducts and air handler located in conditioned space boundary, 100% visible, and not located in an enclosed space such as a chaseway, interior or exterior wall or roof cavity or in an enclosed floor cavity."

EStar says you have to test BOTH total leakage and leakage-to-outside on every house, with a few exceptions some of which you mentioned.  I think V 3 has overreached on a lot of topics, this total leakage number being one of them.  

Here is another topic:  Next time you do a duct-leakage-to-outside test, when the test is done, leave the equipment running with the leakage number showing on your manometer.  Then pull the tape off the registers one at a time.  Check the leakage number on the gauge.  If the house is reasonably tight  (let's say 4 ACH50), the number won't change even with all registers open - you didn't have to tape!

Ed Minch


Latest Activity

Summer Reyes posted a blog post
39 minutes ago
Oliver Periman is now a member of Home Energy Pros Forum
8 hours ago
Bob Krell joined Tom White's group

Trainers and Mentors

Share your experience with different training and mentoring methods. Learn about new training…See More
Bob Krell replied to Bob Krell's discussion What Do You Do When You Find Suspected Mold? in the group Healthy Indoors (IAQ)
"Most of the moisture issues there can be attributed to failure to get the roof system completely…"
Bob Krell replied to Bob Krell's discussion What Do You Do When You Find Suspected Mold? in the group Healthy Indoors (IAQ)
"You are correct about it being multi-family.  It is, in fact, an assisted-living facility, so…"
Quinn Korzeniecki added a discussion to the group Building Performance Institute (BPI)

Weatherization Pros: Only 9 Days Left to Apply for Free BPI Certification Exams!

Are you a weatherization professional? Don't miss your chance to get the costs of your new 2018 BPI…See More
Quinn Korzeniecki posted a discussion

Weatherization Pros: Get BPI Certification Exam Costs Covered!

Are you a weatherization professional? Don't miss your chance to get the costs of your new 2018 BPI…See More
Diane Chojnowski replied to David Butler's discussion Beginners Guide: Managing Subscriptions on Home Energy Pros
"Great guide David! Thanks! We send two weekly emails to keep members in the loop about new blogs,…"


  • Add Photos
  • View All

© 2017   Created by Home Performance Coalition (HPC)   Powered by

Badges  |  Report an Issue  |  Terms of Service