Replies

1. 
   roger g | Dec 25, 2005 04:31am | #1

   Usually sealed combustion chamber are in a direct vent furnace.  Direct vent brings in the combustion air from outside and doesn'r use any air from inside the building therefor if it isn't sealed it is getting air from the room and ain't direct vent.

    Direct vent venting(chimney) vents to the outside either through the wall or the roof depending what is easier or code.  There are rules as to where you can vent PLUS the manufacturer has their own standards. Usually the air coming into the furnace comes from very close proximity to where it is vented. Maybe only 6 inches apart.

    

    

   roger

    

    

   roger

1. 
   rjw | Dec 25, 2005 06:09am | #4

   >>Usually the air coming into the furnace comes from very close proximity to where it is vented. Maybe only 6 inches apart.But be careful to follow the manufacturer's specs - if the air intake starts pulling from the exhaust flue, it'll turn the furnace into a big time CO producer and generally screw up the combustion.Typically, the exhaust has to be above the air intake.Each manufacturer has its own specs, but, except for concentric set up, I can't think of any that spec less than 12" (or maybe 9")I saw one screwed up set up where the air intake was almost completely plugged by icing condensate since it was pulling flue gases in. I took a pic, but haven't seen it in a long time and forgot where it is.

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1. 
   roger g | Dec 25, 2005 09:24am | #5

   I used to install high efficiency furnaces for years and I believe it was Carrier that was about 6 inches apart. One pipe snorkled up and the other snorkled down so even though the pipes were relatively close together the openings were a little further apart usually 12 inches apart

    The freezing up of the intake pipe is a VERY common occurrence which is why in some cases we used to increase the size of the pipe of the intake where it comes out of the house just like the vent pipe on the plumbing stack.

   Oooops. Just pulled out an old carrier install manual and it is 12 inches between the ends of the pipes.

    

    

    

   roger

2. 
   floorheater | Dec 25, 2005 04:46am | #2

   There are some oil (utica for one) that uses direct vent, only one penetration to the outside, it uses a collar for the fresh air that it draws directly from outdoors and cools the exhaust pipe in return very good eff. also.

    

    

     

3. 
   DaveRicheson | Dec 25, 2005 05:25am | #3

   Direct vent furnaces, or condensing type, can get their combustion air from a separate pipe to the outside, or from inside the house.

   I just put one on my shop and chose to bring the combustion air from out side. This allowed me to completely seal the mechanical room, except for return air. I am filtering the return air through a 24x24x2 pleated filter in the door and another 16x25x2 filter on the unit.

   I chose to use outside air for combustion to reduce any dangers involved in finishing projects in the shop. The double filter arrangement is additional dust control for what my dust collection system doesn't catch.

   Most direct vent units that I looked at came with pretty good instructions for several different methods of installation. Check the installation instructions and local codes for locations allowable for venting and intake air.

    

   Dave