Outside Combustion-Air Intake

Outside Comb. Air Stub Pipe (in firebox) In houses which are built extremely tight (for energy conservation), ALL flame-heating systems should use outside combustion air. This includes the conventional house furnace.

What this means is that the fire will use air that came from outdoors rather than air which came from inside the house, which used to be the common procedure. In super-tight new houses, using house air doesn't work, because in order to use up some house air (and make it go up the chimney), OTHER, OUTSIDE air would have to get into the house to replace it. And the tight construction doesn't allow enough air leakage in to do this. The net effect could be that smoke wouldn't go UP the chimney, and if somebody turns on a bathroom ventilator or a kitchen exhaust fan, smoke may actually come back DOWN the chimney to replace THAT air that was leaving the house!

Such a situation contributes to the modern concerns about indoor air purity in tight houses. Therefore, outside combustion air sources are appropriate to these very tight houses. In older, looser houses, these concerns are probably unnecessary.

By the way, there is a provision that has a very similar name, Outside Makeup Air, that is quite different. Even many experts seem to sometimes confuse these two or to blur them together. If you want information on THIS topic, Click HERE.

This option on a JUCA involves our permanently welding a 3" or 4" stub pipe through the wall or floor of the firebox of the JUCA. There is a little shroud over the opening at the firebox end to minimize the chance of sparks or ashes going into this passageway (as seen in the first drawing).

Text Font Face
Text Size
(for printing)
Outside Comb. Air Stub Pipe (outer end) In order to use this option, it is necessary to connect the other (outer) end of the stub pipe to the air outdoors with aluminum or galvanized duct materials (the JUCA's stub pipe outer end sticks out a couple inches beyond the JUCA's body as shown in the second drawing), so the air for the fire has to come from the outdoor source you planned. (The draft control on the front of the JUCA would be closed.) You should consider putting a damper or some other air control in that combustion air intake path, so that you can affect the fire. (The JUCA-installed stub pipe does NOT include such a control.


You have a variety of choices as to the location of this intake stub pipe in the firebox. Depending on where your combustion air source is, you may wish to specify one of the following. If it is not important just where it is located, JUCA production people will put it in a reasonable location.

On free-standing JUCAs, it usually doesn't make sense to choose any of the side wall choices, since that would cause the pipe to be in a very visible location on the outside of the side of the unit.

The JUCA Home Page is at: http://mb-soft.com/juca/index.html

E-mail to: cj@mb-soft.com