Best MD8T Installation Guide

OUTSIDE AIR INTAKE LOCATION
Proper design and location of the outside air intake location is critical in

ensuring that the Damper can safely and reliably provide an opening for

fresh air to enter the home. The following requirements for the location

of the outside air intake must be met:
•  Outside air intake is located a minimum of 10’ from combustion ap-

pliance vents, chimneys, plumbing stacks, and bathroom or kitchen

exhaust vents. If local codes have more stringent separation re-

quirements, they shall apply.

Installations will vary according to the location in the home where the unit is installed and which model Damper is used. Use the following

illustrations and notes as guidance for your own installation. Always comply with local code requirements and in any instance where a detail

shown below conflicts with local code, the local code provision shall apply.

•  Outside air intake is placed high enough above grade to prevent

blockage from snow or other debris such as leaves, and at a mini-

mum of 1’ above grade.

•  Make-up  air  damper  should  not  draw  air  from  crawlspaces,  ga-

rages, attics, adjacent dwelling units, or any enclosed part of the

building. The Damper should be installed to draw air directly from

outdoors.

OUTSIDE AIR INTAKE OPENING PROTECTION
Because the Damper, together with the end cap and outside air duct

which are installed with it, will allow outdoor air into the indoor environ-

ment, it is important to meet the following requirements:
•  Model 641FA (6”) and 643FA (8”) fresh air inlet wall caps include

protective  bird  screens  to  keep  out  animals  and  outside  debris.

Clean screens often and do not remove.

•  If a protective bird screen other than the screen provided is used, it

must cover the entire opening of the outside air duct. This screen

must also have openings of at least ¼” but no larger than ½”.

•  The outdoor air intake opening should meet local code provisions

for the protection of openings in exterior walls, including steps to

prevent moisture intrusion around the opening.

Note that the screen over the outside air opening is not a filter. It is

intended to prevent the intake of leaves, animals, or debris into the out-

side air duct. A downstream filter is necessary to remove pollen, dust,

and other airborne particles. Potential filter locations are shown below

in the Typical Installations section.

MINIMUM RETURN AIR TEMPERATURE REQUIREMENTS
HVAC equipment manufacturers may have minimum requirements for

the air temperature in the return air plenum. Introducing outdoor air to

the return side of the central duct system may impact this temperature.

The installer should adjust both the size of the outside air duct and the

location of its connection to the return side of the central duct system in

a manner so that minimum air temperature requirements are satisfied

under design conditions.

AIR HANDLER UNIT

COOLING APPARATUS

AIR DISTRIBUTION FAN

HEATING APPARATUS

THERMOSTAT

CENTRAL SYSTEM SUPPLY AIR

REGISTER BOX ADAPTED

WITH SLIDE-IN FILTER (optional)

AUTO. MAKE-UP AIR DAMPER

FIELD MEASUREMENT OF OUTSIDE

AIR DUCT PRESSURE. (See “Install The

Damper” section on page 3 for damper

balancing instructions.)

FRESH AIR INLET WALL CAP

WITH BIRD SCREEN

INSULATED OUTSIDE

AIR DUCT (slope toward wall cap)

EXTERIOR WALL

VENTILATION AIR INTAKE

(locate away from pollutant sources)

CENTRAL SYSTEM RETURN AIR

FURNACE FILTER

Planning  the  installation  first  requires  selecting  the  most  appropriate

installation approach. The chart below offers suggestions for the most

effective installation approach by considering a few important factors.

Further details on the two main types of installations are provided below.

 

Yes

• House has central duct work?

Yes

• Return-air side of duct work is 

accessible -either the return-air trunk 

or return- air plenum?

Damper connected to 

return side of central 

duct system

No

No

Damper  ducted directly 

to a ceiling, floor, or wall 

register