Why
is it so important to have my ducts sealed?
The most energy consuming appliance in a home, by far, is the
Heating/Ventilation/Air Conditioning (HVAC) system. Ductwork,
whether under the floor, or above the ceiling, is designed to
deliver conditioned air to the rooms through the ceiling or floor
vents which are referred to as supplies. HVAC systems
also have returns which suck the air out of the rooms at the
same time the system is supplying the air. All of this
positive and negative airflow is contained and insulated in ducts.
If those ducts have leaks in them, you are literally blowing your
money outdoors.
What
is the difference between supply side leakage, and return side
leakage?
As explained in the previous faq, an HVAC system has a center.
The center would be where the air is handled, and changed from a
negative air flow (suction) to a positive airflow (blowing).
When there is a leak on the supply side of a duct system, the air
you are paying to be conditioned is leaking to spaces you don't
occupy- like the attic. Should the leak be on the return side
of the HVAC system, air from the unconditioned space where the
return ducts are located, is being vacuumed in and mixing with the
air you are breathing. This scenario puts your health at risk
and costs you money!
How much air leakage in CFM can my change-out or alteration job
have?
In short answer, there are 4 ways to obtain passing results- 3
ways that deal with actual calculated air flow and leakage in CFM.
Those 3 ways are A) 15% of calculated airflow can leak using the 400
CFM per ton formula as explained in the the following question.
B) 60% reduction achieved in comparison to the initial leakage test
performed before the change-out. C) Measure the amount of leakage to
the outside, and make sure it's less than 10%. Measuring
leakage to the outside requires the use of a blower door, and ducts
supplies still have to be taped off. D) Finally, if 1 of the
above 3 passing methods can't be achieved, passing results can be
obtained so long as the contractor seals all accessible visual leaks
and that has been visually verified with smoke by a HERS rater.
How do you calculate the amount of air that is leaking from my duct
system?
In order to calculate the allotted amount of air your ducts can
leak, you must go to 1 of 2 places- the furnace or the condenser.
When looking on the condenser, you'll generally find a model number.
Within the model number will be a number that when divided by 12
will yield the size of the unit it tons. Calculations are
performed with 400 CFM per ton. So a 4.5 ton unit has 1800
CFM. Another way to calculate the air load, is from the output
BTU's of a furnace. If the output BTU's were specified on the
model sticker as 89,000, we would multiply 89 x 21.7 and get 1931.
Since we want the house to be guaranteed in the passing zone, we
will use the smaller of the two numbers to calculate the target
leakage in CFM. To calculate the target leakage, multiply 1800
(total air load) by 15% (allotted leakage for change-outs) and we
get 270. We seal all of the supply registers in every room,
pressurize the duct system with a duct blaster. Sensors are
attached to the duct system, and duct blaster and then channeled
into a manometer (measures static pressure). The system is
pressurized to 25 Pascal (the typical amount of air pressure in a
fully functioning duct system), the manometer reads the amount of
air leaking in CFM.
How much air should leak from my duct work?
For brand newly installed duct systems in which the entire
system is new, the allotted leakage rate is 6%. For all new
construction, the allotted leakage rate is 4% if tested at rough-in,
and 6% if tested at final. For alterations and change-outs,
there are 4 options for a system to pass which are outlined in
question 3 of this page- How much air leakage in CFM can my
change-out or alteration job have?
What is the difference between 100% testing & sampling?
The building codes state that the building owner or the agent of
the building owner, has the option to have the 3rd party
verification performed on their house/building (100% testing), or
they can choose to be part of a sample, in which the installing
contractor makes groups of no more than 7 jobs in which duct sealing
was required, the HERS rater selects 1 job at random, and tests its.
Should it pass the first test attempt, every other house in the
sample group will pass. Should it fail the first test, a
second test must be administered to another random job within the
sample group. Should the second house pass the first attempt,
the first house will be revisited, re-tested till pass. Should
the second job fail the first attempt, the entire sample group must
receive 100% testing.
What is used to test the ductwork?
A calibrated manometer that works with a duct blaster. We
use the Minneapolis Duct Blaster and DG-700 Manometer.
How long does a tight duct test usually take?
Depending on the size of your building, a test can take anywhere
from 30 minutes - 2 hours.
Are there any alternatives to avoid the need of a HERS rater?
Yes there are, regardless of what climate zone you are in, you
have the option to install an EER 12 with either a refrigerant
charge measurement or TXV, plus 0.82 or 0.92 AFUE plus increased
duct insulation.
Is it my option as to whether or not I want to be sampled or 100%
tested?
Yes...this option rightfully so, lays at the option of the
building owner. If they want to be included in a sample, they
must be notified of this, and they have to be informed of their
option to have the 100% testing performed.
What is the benefit of having 100% testing?
Having your building tested is the only true way to guarantee
compliance and minimal leakage. A properly functioning HVAC
system benefits the homeowner in many ways- saves money, provides a
more healthy living environment, conserves fossil fuels, and further
protects our atmosphere.
What is considered 'typical leakage' compared to
other homes?
According to studies, the typical home in California has more
than 30% of air flow leaking from the ducts alone. |
