2012 was the first year the International Energy Conservation Code required residential construction to pass an air leakage rate test, better known as a blower door test. My area of the country requires the test to be at or below 3 air changes per hour at the test pressure of 50 pascals (ACH50). (Other areas, typically warmer climates require 5 ACH50.) Most new construction in my market has no problem passing the test, but I have had a handful of houses fail, usually the failed tests are by a builder having their first blower door test or the project is a very small home.
My current fee for the typical code required blower door test is $250 (price increases for large and complex homes). If the home does not pass, I begin looking for the causes at a per hour rate of $100. Once the issues are found, someone, usually the general contractor or insulating contractor will have to perform air sealing to correct the deficiencies and the home will be required to have a second test. My rate for a second test is $150 (the fee is reduced because I’ve already calculated the volume of the home which greatly reduces the time on site). This process repeats until the home passes. Without a passing test, most jurisdictions will not issue an occupancy certificate. It’s beneficial to pass a test the first time.
Passing a test
There are a few ways to almost guarantee a passing test. The best way is to understand where houses leak air and design an air sealing strategy with that in mind. There are a lot of great ideas and method to perform air sealing during construction, nothing is overly difficult, a lot of information can be found on GBA and other publication on air sealing.
A way to catch an issue early is to have a mid-build blower door test. This test is typically performed after Mechanical, electrical and plumbing (MEP) systems are installed, windows and doors are in place, but before insulating. The biggest difficulty with this test is how to address a vented attic or roof which is often open to the outside. A method I’ve used is to install polyethylene sheeting on the ceiling, sealed to the wall framing. (I live in a very cold climate; polyethylene is common in my market.) Other areas might use drywall or a smart vapor control product. I’ve also tested with closed cell spray foam installed in unvented roofs and conditioned attics. Problems can be identified with a test and corrections made before insulation and finishing materials are installed.
Another option is to use a third-party air sealing technology, such as Aerobarrier. This process is typically performed at the same point in the building process as the mid-build blower door test, after MEP systems are in place but before insulation and finishing. The Aerobarrier process includes pressurizing the home and then releasing an aerosol sealant fog that is suspended in the air. The sealant floats until it is caught in an air current. This current will lead to a penetration to the exterior where it will build up around the opening until it is sealed. A couple advantages to this method of air sealing is time savings, the process usually only takes a few hours, and the level of air tightness is chosen, you get to pick, the tighter the home, the more time the sealing process takes and the higher the cost.
The Failed Test
As I said earlier, I have blower door tested a few houses that have failed. There can be many reasons for a failed test, sometimes the choice of a product is the reason. I had several failures in a group of duplexes that were built over the course of three years, they failed in part because of the water heater that was selected. The water heater was a natural venting gas unit installed in a small mechanical room. The water heater used interior air for combustion and required a
combustion air vent to the outside. Per the ANSI/RESNET/ICC 380 testing standard, these vents, and the flue for the water heater must remain open during a code compliant blower door test. Simply moving to an electric or some type of sealed combustion water heater would eliminate the required combustion air vent and the homes would have passed.
Another product I still see on occasion is the standard recessed light fixture. You would
think by now builders would know not to use this product in an area where it penetrates the air barrier and displaces insulation. A new home I recently tested failed partially because this type of lighting was chosen. This same home also had an unsealed attic hatch. These two conditions combined with the home being small, 8,000 cubic feet, contributed to the new home failing the test, even though the home was only leaking a little
more than 500 CFM at 50 Pascals. The attic hatch was an easy fix, simply caulk the drywall access panel shut, air sealing the recessed cans, especially in a cathedral ceiling is much more difficult. This contractor caulked the recessed fixture housing to the drywall, which helped some. A better choice is to eliminate the traditional recessed cans and move to the recessed light “look” that uses a thin LED light fixture and a standard flanged air sealing electrical box that can be sealed to the drywall.
As a side note, the 2021 International Energy Code has an option for blower door testing small structures using the cubic feet per minute of air flow per square foot of surface area (CFM50/Ft² of surface area). The structure needs to be 1,500 square feet or smaller and must achieve a leakage rate of no more than 0.30 CFM50/Ft² of surface area. The home above that failed the standard ACH blower door test achieved 0.15 CFM50/Ft² of surface area. If tested to the 2021 code allowing the CFM50/Ft² of surface area, this home would have passed.
Another common area of air leakage is between the foundation and framing. The new home in the upper photo had a very low blower door test, 1.04 ACH50, but this air leak at the floor was easy to see with thermal imaging. This home will experience very cold wintertime temperatures, there’s a good chance this small area in the master bedroom will have damp drywall in this corner. The lower photo is a home that just passed at 2.74 ACH50. There were several areas around the home where leakage under the bottom plate was evident. Traditionally we are using a sill seal or some other type of gasket to seal the bottom plate to the floor or foundation. I also suggest sealing the exterior sheathing to the foundation using a tape, sealant, or fluid applied membrane to further reduce air movement in these areas.
These two images are of the same new home. Two of the wall mounted mini-split heads are leaking air during the blower door test, I see this all the time. The air is moving around the line set, condensate drain and electrical wire penetration (though some of the air may also be moving through a condensate line that is open outside). Feeding solid copper piping through a wall and making the connection to the head, often after the home is finished makes air sealing tough. In new projects I’m involved with, I try to move the heads to an interior wall, right next to an exterior wall and run the line set before finishing whenever possible. A small amount of slack can be provided in the tubing to allow for some movement and adjustment to the line set without breaking the air seal.
The biggest area of deficiency in air sealing I see in both old and new construction is properly addressing the ceiling or roof. Even a simple roof, which I rarely see in new construction, can be a challenge to air seal. A good air sealing connection between the wall and roof is often missing. There are interior wall intersects that prevent continuous air control. We then poke a bunch of holes in the air barrier with plumbing pipes and electrical wiring and boxes. Add a forced air heating system with ducts in the attic space, now there’s a whole bunch more holes. Change the simple roof to one with multiple roof lines, dormers and cathedral ceilings, air sealing just became a nightmare for even the best at building very tight structures. With that said, the ceiling is the most critical area to get right.
The second most important area to address is low, connecting the foundation to the
framing. Tying dissimilar materials together to form an effective air seal can be tough. Concrete foundations and slabs rarely end up perfectly flat. The dips and humps can create a pathway for air to move into the structure. This is where I prefer to see a belt and suspenders approach, gaskets with the addition of tapes or sealants.
I see less issues with air sealing walls, but there are still some. There are several good options on how to air seal a window or door. We punch several holes that connect the inside to the outside with electrical wires, vents and outside water spigots. These need to be made both water and airtight.
Blower door testing is not going away, I wouldn’t be surprised if in future energy codes, the requirements for building tightness become more stringent. With a basic understanding of where a home leaks air, a strategy can be designed, and a code compliant blower door test can be passed the first time.
This is what I thought today, I am installing Mini Splits here in Germany and thought how the condensate tube will pass the blower door test. Any suggestions on this. I thought of, a siphon could work, before moving the drain line outside. The siphon should be inside in cold climate zone to prevent from freezing. Otherwise I have no clou. The line set and wiring should be easier, seal it with a hybrid grout should work. Thanks in advance for an advice. Carsten from Germany
Hi Carsten,
I believe what you refer to as a siphon in Germany we call a trap across the pond. A way to keep a little water in the pipe so that the open drain line does not allow air to enter the home. Yes, the trap or siphon will need to be located inside the home in a cold climate to keep from freezing. You might want to refer to the manufacturer’s instructions when it comes to adding a trap or siphon, I have seen someone place a loop in a plastic drain tube for this purpose, the loop must have air locked and caused the condensate drain in the heat pump to overflow, resulting in some water damage to the home. A little air leaking into the home is better than water damage. That being said, if you can block the flow of air without causing the condensate to overflow, you can improve the air tightness of the home.
As far as the rest of the piping and electrical, if it is possible to run the pipes separately, through their own hole instead of grouping them together, you can see a reduction in air leaks. Sealing a hole with one pipe is easier than trying to seal a hole with several pipes. I do see a lot of air leaking around these pipes during blower door testing, especially in existing homes where it’s more difficult to install the line set and electrical. We can do a much better job in new construction.
Thanks for the question!
Randy
We fail our test because our house is too well insulated, so we are below building air standard. What do we do now, remove some insulation? Our house was built in the 60’s, but we recently did an addition. We had this energy test done, due to solar insulation. We called a couple of HVAC companies to see if there is a ventilation system to installed and no one does this. We currently just have a few windows cracked to hopefully help with the issue.
Hi Nancy,
If I understand you correctly, you had a blower door test completed which suggested you should have a mechanically ventilated system added to your home. The system that is code required in my state of Minnesota for every new home is called balanced mechanical ventilation, sometimes referred to as an air exchanger or energy ventilator recovery (ERV). We install a lot of these systems that are manufactured by Broan. I might be able to help but need a little more information. Where are you located, city and state?
Randy
Some good stuff in this article. Great visual examples with all the thermal imaging.
The only thing that concerns me is what you said about the attic hatch. Caulking it shut sounds more like a temporary fix than an actual fix, since the first time someone pushes it open to get into the attic, that caulking is ineffective from then on. Wouldn’t it be better to stick on some adhesive weather stripping around the hatch? Also an inexpensive and easy fix, but will actually have a shelf life before needing replaced.
Hi Mario,
I agree, weatherstripping is an option. Lately I’ve been seeing a lot of attic accesses in the finished areas, hallways are common with many being sealed by the drywall taper. When someone needs access later, they cut the drywall tape. Caulking will reseal the access with a cleaner look.
Thanks for the comment.
Randy
I had a house fire (2023) and since my house was taken down to studs I have to pass the door blower test. My standard is a 3 (house built in 2014) and the house tested at a 7.4. I understand what that means, but am doing everything they said and am not sure how to decrease so much. I have taken every outlet off, put in foam insulation in the box, a foam outlet on the face plate, and caulked the over 200 outlets and switches in the house. I recaulked all the windows, window trim, and air registers. I have gone as far as to buy a $450.00 Flir camera to see thermal, but while I think that helps with energy conservation efforts, I don’t know if it will help the blower test.
Is the number calculted by square footage of the house? Should the doors be open or closed during the test? Should I seal off the doors like the closets to improve my reading? Should I tape off the exhaust fans in the bathrooms and laundry room? These efforts seem as if they will be minimal to me, but I am trying to pass this test as I have to pay $250 every time they come.
If I had known about the air barrier spray I would have done that, but I now have furniture in the house and the house is painted with new flooring so not an option.
Do you have any suggestions for me or places that I can check to pass this test?
Hi Kelly,
Can you get me the test results from the person performing the test. I’d like to see the CFM50 number. If possible, the size of the home would also help. The volume is used to calculate the test results so I would need length, width and height. If you have an irregular shape or roofline, vaulted ceilings and or attic knee walls like you would find in a cape cod design, I’d also need those dimensions. If the home is less than 1500 square feet, there may be another metric that can be used, but that would be up to the building official to accept the new code language.
Randy
Hello! I have a duct and air leakage test form. It doesn’t have a CFM50 number. It does have a CFM25 number- for zone 1 it shows a 72 with a ring 3 used and for zone 2 it shows a 55 with a ring 3 used. My form says the cond. area is 3400 square feet which is based on the local appraisal district which shows it is 4 bedrooms and 2 baths, however, I have five bedrooms and four baths. I would say it is more likely that I have between 3900-4000 square feet. I don’t know if I can have that changed without some type of major headache and I am not sure how much of a difference that would even make???
Hold up!!! I see something on the form that says blower door reading CFM50 and it shows a target of 1360.0. The blower door reading ACH50 is a 7.4.
If I am reading it correctly the total duct leakage passed (and the duct leakage with respect to outside passed (total target 0.0 and total reading 0.0)
The house is pretty normal looking. It has no vaulted ceilings. The ceilings are nine feet except in the entry way (those are probably about 22 feet). It is a very open concept home. I will contact the builder for home dimensions. I had a house fire and don’t have that information since it burned. Thank you!
Hi Kelly,
CFM25 would be the test results for a duct leakage test. If the test is showing two zones, there would have been two tests completed. 72 would most likely mean 72 CFM for the first zone test and 55 would be 55 CFM for the second. I would say that the duct tightness test would pass (I don’t know where you live or which code version is in enforcement in your area). I come up with roughly 2.66 CFM/100 Ft² of conditioned space. The 2021 code requires less than 4 in most cases. You also mentioned total duct leakage to outside is 0.0. This is a different test than the standard duct leakage test. If none of your ductwork is located in an unconditioned attic or crawlspace, then duct leakage to outside would be 0.0. If any ducts are in a vented attic or vented crawlspace, which both are outside the building envelope, then 0.0 means the installer got the installation perfect. (Not common, but it could happen.)
As far as the blower door test, 7.4 ACH50 is above what would be allowed by code, again, I do not know where you are located. You would need to be under either 3 or 5 ACH50 to pass current codes. Your test results seem high based on the square footage of the home. A home with 3,400 square feet and 9′ ceilings would have a volume of 30,600 cubic feet. A blower door test result of 1360 cfm50 would have an ACH number of around 2.66 ACH50, a passing test (if the volume is indeed around 30,600 cubic feet). For the 7.4 ACH50 test result and 1360 CFM50 number to work out, the volume of your home would have to be closer to 11,000 cubic feet. I would have the person who performed the test double check their volume calculation.
If you can get me a copy of the actual test data, I can get a better idea of what might be going on. You can email me at: northernbuiltpro1969@gmail.com
Randy