Miller M3 90+ Installation Tips

The M3RL furnace series are condensing gas furnaces and must be vented with PVC or equivalent pipe to prevent vent corrosion. Using the replacement vent caps in the kit, you may easily install the vent and combustion air intake pipes for the new furnace utilizing an existing roof jack as a chase. Before installing, verify the structural integrity of the roof flashing and upper and lower combustion air pipes. Note: do not use this kit with existing roof jacks that are not sound. When replacing the existing furnace with the new M-3 furnace, remove unnecessary parts from the old roof jack. Disassemble the top from the roof jack by removing the screws.

Larger Diagram
After removing the top assembly, remove any braces or supports which secure the inner liner pipe, remove the inner liner pipe. To install vent and combustion air intake pipe, install 2 rubber couplings on the furnace pipes and assemble 90 long radius ells. Place the bottom and top replacement caps on the roof jack, do not screw the caps down at this time. Cut 2 plastic pipes and route the vent and combustion air intake pipes through the replacement caps as shown in figure2. Note: The maximum height from the top of the furnace to the top of the flue pipe must be no longer than 13 feet. Join all the pipes and elbows using appropriate plastic solvent cement. Screw the top and the bottom replacement caps to the outer pipes. Note: At least two screws must be used on each cap. Tighten the upper hose clamps on the 2 rubber couplings. Secure the combustion air intake pipe to the lower combustion air intake pipe at the bottom of the upper pipe using at least two screws. Seal around the two pipes on the top and bottom replacement caps with silicone sealant.