Originally Posted By: wdecker This post was automatically imported from our archived forum.
Do any of you have any requirements for a high efficiencey furnace that has a combustion air supply pipe and a vent flue pipe?
Most of the time I see them coming out the side of the house and I write that the intake pipe should be below the exhaust pipe and have at least 3' of seperation, so as not to draw combustion gasses back in.
I see a lot of them in attics, and most of them do not have the intake pipe installed, they draw their combustion air from the attic area. I usually defect this, mainly because I also see blown in cellulose insulation that is firable.
Originally Posted By: wdecker This post was automatically imported from our archived forum.
Blaine;
that's 3 feet seperation. I have heard that from a few licensed HVAC people.
When I inspect an attic furnace and see that it is a high efficency and it has no intake vent and there is blown in cellulose insulation th the same attic, that is how I get it.
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
Sorry, I misread your distance
The intake and exhaust pipe on many furnaces is contained in a single combinaton fixture on the exterior, so three feet would be a bit overboard. Those fixtures are within three to six inches between intake and exhaust.
Originally Posted By: apfaff This post was automatically imported from our archived forum.
I have seen this on several inspections but not in the attic. I asked several HVAC guys and they all said the manufactures specify the pipe routes and separation. I always say “Have it evaluated and consult manufactures specifications as this is not a typical installation”. The overwhelming feed back has been that they repair it and was most likely a do-it-yourselfer or lazy installer without pulling the proper permits. Sorry I cant Quote an exact code.
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
My gut thought is that there shouldn’t be a problem with the pipes closer together than 3’. I can’t find a separation distance in any of my books, so it is probably manufacturer specific. If the exhaust was backing up into the furnace, you should be able to see that by the color of the burn, as it would be very inefficient.
As far as installs in an attic, that was normal when I was in VA. The pipe was usually at least 1' above the insulation floor though. Remember, the intake is for combustion air, not for return air, so if the heat exchanger is intact no fibers should ever get into the house.
Vermiculite  Possibility of asbestos. Recommend testing by an industrial hygienist, asbestos company or rocket scientist!
Now for the disclaimer. It's been three years since I've seen a gas furnace!!! All electric here
Originally Posted By: Lee Hammerstein This post was automatically imported from our archived forum.
Most high efficiency furnaces recommend the exhaust and intake be located on the same side of the house. The reason is because the pressure of the wind blowing into a pipe on one side of the house would be different than on the other side of the house (and different in the attic). Having the exhaust and intake on the same side equalizes the effect of the wind.
Manufactures specify the termination method and I've never installed a furnace that required at least three feet separation. Lennox supplies a termination plate and places the exhaust and intake within one foot of each other.
If you have a question about venting check the installation manual. It should be near or in the furnace.
