22
Add-On Furnace (Supplementary Heat installation)
To install the Magnum 7500 as an “add-on furnace” first set the unit along side the existing
primary forced-air up flow furnace and position so that all maintenance and operational functions
can be performed.
Attach the section of ducting that will have the fan-limit control installed in it and then install the
back draft damper (CF20). This prevents air from the existing furnace from blowing back into the
Magnum 7500 and causing damage to the electrical system when the Magnum 7500 is not in use.
Install the 12” round 26 gauge galvanized ducting, elbows, etc. up and into the existing supply
plenum. Next, connect the cold-air return ducting. A minimum of 12” round must be used for the
cold-air return. Determine the size required for this installation and attach to the back of the filter
panel.
Order part # CF28 to convert cold air return from rectangular to 12” round.
Return air is very important to the furnace operating properly. Adequate heat distribution will not
happen if the return air is not hooked up or adequate.
Failure to supply adequate return air will
void the warranty on the furnace.
Complete the venting, electrical and thermostat installation as per the instructions in this manual.
Back Draft
Damper
CF - 20
Optional 12”
round adaptor
plate CF-28
When installing into another
furnace system you must install
the CF29 high limit protection
thermostat into the supply
plenum on the existing central
furnace. The 200 degree high
limit control thermostat must
be located under the plenum
coming from the Model 7500
Corn furnace. Typical
installation would be directly
above where the supply
plenum starts on the central
furnace. Install the wiring as
directed on the wiring diagram.
