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15
Indirect 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 permits localized exhaust of indoor air and uses the
existing forced air system to distribute fresh air.
Although independent room balancing of exhaust air can be achieved with the
indirect duct system, the distribution of fresh supply air cannot be balanced.
Where required by local codes, the HRV/ERV supply duct may be directly
connected to the furnace return air 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.
This method of installation requires that the forced air circulation fan be
operated when the HRV is in use.
Please refer to fig II. below.
fig. II
Stale Air
Exhaust
Fresh
Air In
Fresh Air
Supply
Minimum 36"
Stale
Air Out
Breathing "T"
