Therma-Stor Products Group UA-135H - Manual (Page 6)

Duct Sizing: For total duct lengths up to 25', use a minimum 10"
diameter round or equivalent rectangular. For longer lengths, use a
minimum 12" diameter or equivalent. Grills or diffusers on the duct
ends must not excessively restrict airflow.
Isolated Areas: Effective dehumidification may require that ducting
be branched to isolated, stagnant air flow areas. Use 8" or larger
diameter branch ducting to each of two or three areas, use 6" or
larger to each of four or more areas. Provisions must be made to
provide airflow from supply locations to central return location. Proper
air distribution is important to ensure even humidity control and heat
distribution throughout the structure.
Connecting to existing HVAC systems: An optional 10" check damper
is available from the factory to prevent reverse flow through the
UA-135H. If the UA-135H is ducted to the supply of a high static air
handler the check damper may be placed in the UA-135H supply duct.
Contact the factory when connecting to a static pressure of greater
than or equal to +.5" WG.
4.5D Ducting for Fresh Air — Option
Fresh air can be brought into the structure by connecting an
insulated duct from outside the structure to the 6" inlet of the
optional filter box and by turning on the fan switch or activating
the humidity control (on units with the humidity control panel).
Activate the ventilation timer on units with the ventilating & humidity
control panel to bring in fresh air. Refer to section “Programming
Instructions” for the ventilation timer. Advantages of this form of
ventilation include:
1. Outside air is filtered before entering the building.
2. Outside air will be dehumidified before entering if the UA-135H
is running in dehumidification mode.
3. Drawing air from outside and blowing inside aids in slightly
pressurizing the structure. This helps prevent dirty and humid
air from entering elsewhere. It also reduces the potential for
carcinogenic radon gas to enter and provides make-up air for
open combustion and exhaust devices like the clothes drier,
fireplace, and water heater.
4. Exhaust fans are recommended in the bath rooms and kitchen.
In cold climates or areas where the outdoor dew point is low
at times, ventilation can be used to dehumidify the structure.
This is accomplished by bringing the dry, low dew point air into
the structure during these times. This approach is often more
economical than running the dehumidifier to remove excess
moisture from the structure. In cold climates, it is critical to
adequately ventilate to reduce the inside moisture content to
avoid moisture accumulating in the wall cavities. For example; in a
house that experiences condensation on the interior surface of the
windows during the winter, increasing the amount of ventilation will
often cure the problem.
An insulated 6" diameter duct is generally sufficient to provide up
to 125 CFM of outside air. Large quantities of outside air will impact
UA-135H performance positively or negatively, depending upon the
inside and outside air conditions.
The outside air duct should be connected to the 6" round collar on
the filter enclosure of the unit. The amount of fresh air should be
based on the size and occupancy of the residence. If you are unsure
of your ventilation air requirements or have need for higher air flows,
consult the factory by calling 1-800-533-7533 for assistance.
4.5E Installation in a Basement or Crawlspace
with an Existing Forced Air HVAC System.
Basement Installation: Install a separate 10" return for the UA-135H
in a central area of the structure. Duct the supply of the Ultra-Aire
to a 10" x 10" x 10"tee/damper, adjusted to 20% open to the
basement. Duct the other side of the tee to the air supply of the
existing HVAC system. Connect a duct from outside to the 6" collar of
the Ultra-Aire if you wish to provide fresh make-up air. See Figure 6.
Crawlspace Installation: Install a separate return for the UA-135H
in a central area of the structure. Duct the supply of the UA-135H
to a 10" x 10" x 10" tee/damper that is 20% open to the crawl
space if desired. Duct the other side of the tee to the air supply of
the existing HVAC system. Connect an insulated duct from outside
to the 6" collar of the UA-135H if you wish to provide optional fresh
make-up air.
If the existing system has multiple returns, select one to disconnect
from the existing forced air system and use it for the dedicated
FOR HVAC INSTALLER ONLY
6 Ultra-Aire 135H Installer’s & Owner’s Manual