How to Connect an Outdoor Boiler to Preexisting Duct Work

Fitting the Heat Exchanger

• 1

  Locate the furnace supply plenum. The supply plenum is of a box-shaped passage made out of galvanized steel sheets. The passage sits on top of the burner combustion chamber and curves into the supply ducts that deliver warm air throughout the home. The heat exchanger for the outdoor boiler will insert into the top portion of the supply plenum just above the burner combustion chamber.

• 2

  Measure the dimensions of the outdoor boiler heat exchanger. Measure the width and the thickness or girth of the unit.

• 3

  Cut a hole in the supply plenum duct with a jigsaw. The hole’s dimensions should equal the width and thickness of the boiler’s heat exchanger.

Installing the Heat Exchanger

• 4

  Insert the boiler heat exchanger into the supply plenum hole to make sure it fits. The coil surface of the heat exchanger delivers the boiler's heat to the supply plenum, so this area must fit completely inside the supply plenum opening. The exchanger also has a header area and tubes, which can protrude outside the plenum opening. The tubes and header area carry hot water alongside the coil surface, which is how heat moves into the heat exchanger unit.

• 5

  Create braces to secure the heat exchanger in place, once it's installed, with L-shaped metal brackets along the inside surface of the supply plenum walls. Drill through the supply plenum to set the brackets in place with 4 1/2-inch sheet metal screws or pop rivets. The brackets should run the length of the heat exchanger so that their edges rest against the unit and hold it in place. Use four brackets: two along the top and two along the bottom of the heat exchanger.

• 6

  Seal the boiler heat exchanger to create an airtight unit. Apply adhesive-backed foam tape around the water coil that runs along the front part of the exchanger. The water coil sits in between the header and the water supply lines.

• 7

  Insert the boiler heat exchanger inside the supply plenum.

• 8

  Seal off the heat exchanger opening in the supply plenum. Apply foil tape around the heat exchanger and the gaps between the unit and the supply plenum walls.