Measuring duct leakage with a DUCT BLASTER
Air duct
leakage can increase heating and cooling costs over 30%.
The EPA
reported that most American houses have uncontrolled leakage that
varies wildly from one day to another, but on-the-average have 70%
to 100% of an air change per hour.
This “natural” air leakage averages 100% to 200% more
than the 35% of an air change per hour recommended for homes by
ASHRAE Standard #62-1989 “Ventilation for Acceptable Indoor Air
Quality”.
The Duct
Blaster is a device that uses pressure testing to find the amount
and location of air leakage in a duct system. To do the test, we seal
all the outlets except for one on the return side of the system (the
side that returns stale air to be reconditioned). The Duct Blaster
is connected to that last one and then turned on to blow air into the
ducts. The air goes through the return ducts to the air handler and then
through the supply ducts. If the whole system is very tight, it doesn't
take much airflow through the fan to pressurize the ducts. If you have a
big leak, like a disconnected plenum or duct, it will be impossible to
pressurize the ducts adequately.
The
process yields quantitative results because testing requires two
pressure measurements: one inside the ducts and the other inside the
fan. The first allows the tester to compare results from different
systems by always pressurizing to the same level. The second measures
the airflow in the fan when that level is reached. As mentioned above,
tight ducts mean low airflow, and leaky ducts require lots of airflow.
Pressurizing
only the ducts determines the total leakage. That includes the air that
escapes into the conditioned space and the air that leaks to outside of
the building envelope (i.e., the attic or crawl space). The latter is
the most important part because you derive no benefit from it. To
separate it from the total leakage, we will pressurize the house to same
level as the ducts with the Blower Door. Then, when the Duct Blaster
brings the ducts up to the required pressure, none will leak to the
inside of the house because it's at the same pressure as the ducts. The
fan only has to blow enough air in to make up for the leakage to the
outside, and that's the amount that's important.
In
a tight air distribution system, the leakage to the outside (in cubic
feet per minute, or cfm) will be 5% or less of the square footage of the
house. Most new installations start at about 15 to 20%...and go downhill
from there. At those rates, a third of the heating and cooling bills
could be a direct result of duct leakage.
Measuring house air leakage with a BLOWER DOOR
Air leakage
can increase heating and cooling costs over 30% and contribute to
comfort, health and safety problems. Finding hidden air leakage
sites, called
bypasses,
can be difficult without the use of a blower door. This diagnostic
equipment uses a fan to pressurize (force air into) or de-pressurize
(force air out of) a building. When the fan operates, it is easy to feel
the effects of
infiltration
– air
leaking through cracks in the building envelope. Blower doors have
gauges which can measure the relative leakiness of a building.
Call Today for
more information!
713 645-4611
or
800-564-0743
For your
Blower Door Testing and Duct
Blaster Testing Services in Houston and
the surrounding area, the phone is answered 24 hours a day.
