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Direct Duct System
Safety Warning
Some Building Code and Combustion Appliance Installation Codes do not allow
location of return air grills or any opening such as a breather ‘T’ in an enclosed
room with spillage susceptible combustion appliances. If combustion appliances
are used, and not yet enclosed in a room, locate the grill or breathing ‘T’ outside
any future wall locations and a minimum distance of 6 feet from the combustion
appliance.
This method of installation is used primarily when it is not reasonable to install
dedicated duct runs from the HRV to the various rooms of the dwelling. In this
installation the warm exhaust and warm supply duct runs from the HRV are
connected directly to the forced air heating system ductwork.
This method of installation does not permit source capture of the indoor air nor
does it permit room balancing.
Where required by local codes, the HRV/ERV supply duct may be directly
connected to the furnace return air duct. Where both the exhaust and the supply
duct are installed into the return air duct the exhaust air duct shall be positioned
upstream at a distance of not less than 1 meter (or 3 feet) from the supply duct.
The supply duct shall be positioned as shown on the attached drawing. In this
application no opening such as a breather ‘T’ is used.
Also, where permitted by local codes, the HRV/ERV supply duct may be
indirectly connected to the furnace return air duct using a breather ‘T’. In this
application, the breather ‘T’ in installed into the HRV/ERV supply duct before
the connection to the return air duct. Leaving a gap in the ventilation supply
duct in place of the breather ‘T’ is acceptable but not recommended. In this
installation, a grill is placed in the furnace return air duct and the HRV/ERV
supply duct is pointed at this
grill at a minimum distance
of 100mm (4”) but not greater
than 300mm (12”). The free
area of the grill shall not
be less than the free area of
the supply duct. Call backs
have occurred because it was
thought that something had
been accidently left out of the
installation.
The Direct Duct System
method of installation requires
that the forced air system
circulation fan be operated
when the HRV is in use.
Please refer to fig. III.
Stale Air
Exhaust
Fresh
Air In
Fresh Air
Supply
Minimum 36"
Stale
Air Out
Breathing "T"
fig. III