I am building a new page on our website www.retrotec.com, to help those looking for information on duct testing and adhering to duct testing codes.  If anyone out there has tips or tricks that relate to duct testing or duct testing code compliance, please share.  Any submission posted on the site will be cited with company name and contact information.


You can email them to: silvie@retrotec.com


Thanks everyone.

Tags: Code, Duct, Energy, HVAC, Testing

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SMACNA is typically the universal standard for sheet metal practices of course, but also have the standards for leak testing of any duct system.


There are various degrees depending on duct pressure glass, but most residences are not over 2.0" pressure class and most are 1.0" or less. (They would tend to operate at no more than 0.50" WG in any case.)




SMACNA - HVAC Air Duct Leakage Test Manual

Item #: 210-1143-85
Author: SMACNA
Publisher: SMACNA
Format: Manual

Your Price: $90.00

I have a few tricks none of which are probably not new or original

One of my tricks is a manifold for the tester. The plastic interface for the return is too small. The manifold allows me to use less tape for sealing and speeds up the process.I use mdf 1/4 inch. It broke recently I am contemplating what product to use next.


Ceiling returns have caused more time and problems than any other facet of duct testing for me. I am still in search of the perfect solution.

On ceiling returns i wedge a a paint pole pole to wedge the manifold up against the return to hold it in place. the weight of the hose tends to make this connection difficult. It reduces the loss of bond from tape when powering up. I will use  duct tape at times to improve the bond. If it really becomes problematic I run a screw into the ceiling and patch it with caulk before I leave.

I carry red rosin paper for large gaps.

I bring a rag and cleaner for areas tape does not stick.

In problem areas where tape does not want to stick I will lay on strip on the wall first and then tape to that strip

I recently purchased a product for vents. Here in California we can seal against the drywall. Title 24 requires the return register box be sealed to the wall.

The product called a vent cap. The cost was too high but the complaints I have received over time from my green customers made me bite the bullet. Having used it only a handful of times I am impressed. it improves speed and works well and no more tape.

I always power up the fan speed slow and check all my connections before running to a full 25 pascal looking for loose tape and missed registers.


There are several methods for duct testing that are allowed here in California.  For existing duct residential testing, California allows a duct leakage to outside test. The maximum allowed flow for this test is 10% of the nominal blower capacity.  The advantage of this test is that no supply or return registers need to be sealed or taped.  You pressurize the duct system at the furnace/ air handler relative to the outside to 25 Pa.  This is easy if the furnace/ air handler is in the garage, for example.  Then, using a blower door, you pressurize the house to 25 Pa. Since there is no pressure difference across the air supply/ return registers located in the house, none of these need be sealed.  The total leakage you read at the duct blaster is duct to outside leakage only.  


If you don't have access to a blower door, then a total duct leakage test may be done.  In this case all supply and return registers need to be sealed.  There is a product called duc-bloc that I have used that can speed up the time required to seal the registers.  The product creates a seal using a rubber gasket on the sheet rock wall or ceiling around the register.  This product is great for hard to reach ceiling or wall registers.  I still use painter's tape for floor registers.

There are some rules of thumb for the size of duct leaks.  Sealing the boots on all registers can reduce duct leakage by as much as 5-10 cfm per boot.  Small 2-3 inch x 1/2 inch leaks in the return plenum can leak 75-100 cfm.  In the supply plenum near the blower, very small holes or gaps can cause major leaks (> 100 cfm).  


If you have excess leakage and need to find out where the leaks are then one method is to cut a small hole in the tape of each sealed supply/return register and verify that that duct is pressurized to 25 Pa using another manometer.  If it is significantly less, then you have a problem with the duct that feeds that register.  I have found completely disconnected ducts using this method.  


For duct registers in commercial buildings, I plan on making a 2 ft x 2 ft duct "cover" made from the plastic carpet protector product one can find at Lowe's.  

Thanks everyone, I'll keep you posted on the new page on our site!
I'd like to find out what folks thing about using theatrical smoke during duct testing.  We've done it once when we were trying to get leakage below 6%.  It turned out that the biggest culprit was the new 95% effic. FAU!  The smoke made it very easy to find the leakage locations and we'd do it more but I'm concerned that the smoke will damage our duct blaster.  We have a Retrotec Q32 - Have I already voided the warrenty?

Theatrical smoke is typically made up of diethylene glycol, dipropylene glycol, propylene glycol, or triethylene glycol and glycerin with distilled water.  After sustained use you will see a residue build up that can be wiped up.  It's up to the manufacturer whether to void a warranty.

Hi Troy,


In regards to theatrical smoke with the Q32, I caution you to make sure not to inject the smoke directly into the fan motor, but instead into the edge of the fan housing.  Also, make sure to clean up any residue from the flow sensors, motor and fan housing when the show is over.

Thanks Silvie - Any warranty issues?
What I've done for ceiling returns is had my sheet metal shop make a 16"x25" hemed cover(the most common return size here) with a 10.25" hole in the center for the duct blaster coller.  I have two 2" pieces of thin all-thread through two holes at each end of the cover& two wingnuts on each.  I insert the upper wingnuts through the register & turn them ninety degrees so they catch on the register vanes & then tighten the lower wingnuts.  This holds the cover to the register & supports all the weight.

What about the Dominant Side Duct Leakage Test?

When you set your BD up; you run a routine to set the baseline pressure adjustment.  Then before removing the rings, turn on the AH and watch the change in the pressure differential WRT outside.

A negative change of any size indicates a depressurization, thus the supply side is more leaky then the return side.  A positive change of any size indicates a pressurization, thus the return side is more leaky.  

It doesn't indicate anything about the difference other than it exists.  No change is inconclusive.  It could be both sides are equally leaky, or almost anything else.

Useful if you have one side outside the envelope.


Right now, I'm using the Zip Wall poles and custom made pans to seal the registers.  Very quiick to seal registers and equipment tear down afterwards.  If you plan on doing a lot of duct testing, it makes sense to invest in the set up.

I carry the poles in a ski bag which is much cheaper (on Ebay) than buying the Zip Wall bag.  Be sure to have at least two 20" poles for those house with registers in the vaulted ceilings.

For houses with floor registers, I still use the poles and pans, I just put a new shoe cover over the end to keep from marking up the ceiling.

If you're still using blue painter's tape to seal the registers, here's a simple trick.  Get a couple of cheap plastic tape dispensers that come with the clear packaging tape.  The advantage is that the dispenser has a cutting edge for the tape.  It makes taping registers very quick since you use one motion to pull the tape off of the roll and cut it.

If the registers are on the ceiling or upper wall, I leave a "tail" on the tape so I can pull off the tape in one piece with a reach extension.  It saves having to climb up and down a ladder or step stool.

For return registers, I use painter's 12" wide paper to cover the area not covered by the DB hose adapter.  It's cheap and easy to cut with a utility knife.

For the DB register probe, I use a Dwyer A-303 static pressure probe that has a magnet.  I cut the tip off of the probe and bend it at about a 45 degrees to that it slips in between the register blades.  No more problems with the probe slipping out.

Lastly, if you haven't swapped out your DB duffel bag for one with wheels, you should.

good stuff


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