No announcement yet.

Combustion Air

  • Filter
  • Time
  • Show
Clear All
new posts

  • Combustion Air

    I just had a Rheem Elite system installed. I kept hearing water and waves in the morning and knew the PVC lines were holding water. I have about 12-18 inches of 2 inch pipe on each end but most of the run is 3" for about 12 horizontal feet. They were not pitched toward the furnace for drainage at all. I called them back and they lowered the inside exhaust line about 4 inches (dumping 2 gallons) but not the intake line. When I asked why not both lines the technician claimed no need? Is this true?
    Also I live in SE Pennsylvania and it is not unheard of to have 2-3 feet of snow, even more against my house on the deck. I am nervous if I leave for a couple days and snow builds up over the lines it will shut down freezing pipes and my pet. The technician claimed I can not raise the outdoor lines more or it will add too much resistance? The outside portion is not glued to allow me to adjust it but he just barely fit 2" pipe through the wall. Need I be concerned about this? See Photo attached. What is proper? Thanks

  • #2
    Re: Combustion Air

    Did they leave you a manual? if not tell them you want it in there the give the specs on piping restrictions for the furnace. those look to low and was not a very good spot to vent it if the wind blowing right at the vents it will blow the combustion back at the meter and aything metal and rot it. the gasses are corrosive. for the intake i run them next to the exhaust so they are pitched the same but do not have to be cause it is just bringing in fresh air. also some manufacturers require insulation on some of the venting depending on where it is run.


    • #3
      Re: Combustion Air

      Thank you jcanter for replying. They did leave the installation manual, which is what raised my question about the fresh air tube pitch. Manual says yes pitched for both but some people seem to say it doesn't matter on the intake pipe.

      The tech did say the exhaust had to exit 12 inches from the wall, I guess that is supposed to address the corrosive concern.

      I have a bay window directly to the right, so I think that's why he pointed the exhaust tube left.

      My biggest concern is, if a 3 - 3.5 foot snow drift blocks the pipes.
      The tech said, there is a limit on pipe footage and number of PVC elbows.
      I feel that these pipe openings should be raised a couple feet at least even though he said no, it is too restrictive.

      Now I notice something else wrong, in the manual it seems to call for an installed trap on combustion air intake to catch water so that is doesn't enter the furnace. There is no trap? Here is the manual page.
      Last edited by claudius2k; 11-10-2010, 11:04 AM.


      • #4
        Re: Combustion Air

        Are they serious? Was this job inspected? You need to be 12 inches higher than expected snow line. Here we need to be 4 feet about the ground. I dont think venting on your deck is a great idea. These are things we take in to account when selling a job. You just dont do that because its easier. Get another company out there and fix that before someone dies.


        • #5
          Re: Combustion Air

          In the manual it will list how many ft of piping it can run and how many ft to deduct for each fitting. it needs to be 12" above snow line like heaterman said. sometimes you have to come out low where i am at the extend up outside to get above snow level. I havn't dealt with rheem in yrs but the other brands theres not need for a trap on the intake cause we go up outside then put 2 90's on the top to point down and water doesn't get in. Do you have the model # so i can see if the manuals on line? I think rheem is saying got to 2" comming out of the house to get the velocity to get it away from the structure.


          • #6
            Re: Combustion Air

            post the model # so we can look it up and see how long the exhaust pipe can be and how many 90s you can have .
            i would like to see the exhaust pipe up higher or turned and taken away from the deck if it is not to far to run
            most of the systems i put in they have a tee for the exhaust
            are there screens in the ends of the pipes so birds dont get in

            My seek the peek fundraiser page


            new work pictures 12/09


            • #7
              Re: Combustion Air

              Thank you guys you have been so helpful.
              The model is rgfe09EZCMS, it looks like someone has the manual online at


              On each pipe there is:
              2x 3" to 2" reducers 12" from furnace and 3" from the outside wall
              18 ft 3" pipe
              2x3"ells to angle to furnace
              3.5 ft 2" pipe
              2x2" ells to angle outside visible

              I think the technician's concern about pipe restriction was more, he had already cut the pieces shorter. It appears in the manual it can run vertical up to 60" on the outside but you must insulate the vertical section of the intake combustion air pipe if over 24". I think 48" would probably suffice here. That would be rare but we may have had a very deep snow 20 years ago.

              I suspect jcanter's comment about no trap is common practice here, I was concerned water should not enter the furnace inlet. But outside at the intake, where it called for an elbow termination and they put an ell, I substituted a medium radius 180 facing downward, I doubt any water could get in. They did the job across the street same as mine.
              I didn't have a lot of choice exiting above the deck unfortunately Heaterman. I am thinking just replace those 18 inch risers with 4 foot risers above the deck. Of course it will look like hell, but there are other utilities there.

              Thank You


              • #8
                Re: Combustion Air

                Code or no code I also don't like the proximity to the electric meter, the cable/phone box and is that an A/C cover to the right? (blue plastic)......and for snow, those pipes are way too low and a poor location on the deck.


                • #9
                  Re: Combustion Air

                  Oh, and if there are no grills on the pipes, install them right away, before all those leaves get sucked into the furnace when the wind picks up (also good to prevent mice and birds from getting in too). 2" grills are a buck each.


                  • #10
                    Re: Combustion Air

                    I have had my intake and exhaust get snowed in and it is 9 feet off the ground, do to snow drifting, and I had to make a grill/screen on my intake it is a mess to take a few dead rotting birds out of the intake of the furnace,

                    the first was just a screen that was a flat screen that fit the pipe diameter, and the frost would build up on it and and shut the furnace down, so I took 1/4" hardware cloth and made a cylinder about 16" long, and put a end on the cylinder of screen, and now if it frosts up it still can get enough air to keep it operating and not shutting down,

                    but you want them up where they will not get snowed in, or birds and junk in them,

                    I would follow the manufactures recommendations on the piping if they suggest a trap I would put in a trap,
                    Last edited by BHD; 11-11-2010, 12:28 AM.
                    Push sticks/blocks Save Fingers
                    "The true measure of a man is how he treats someone who can do him absolutely no good."
                    attributed to Samuel Johnson
                    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and the current state of the economy............the light at the end of the tunnel, has been turned off.


                    • #11
                      Re: Combustion Air

                      For PowerVent water heaters, the exhaust, not the intake (on Sealed Shot - Power Shot models) has a trapped drain line feeding off the 3" vent.

                      But remember,

                      That exchange of air from outside to inside goes through a pretty sizeable temperature change and if that outside air carries a high humidity level, then of course; condensation could easily track down and reach the furnace.

                      I've seen many squirrel cage blowers completely rusted on the exhaust side where condensation dripped back.
                      Northern Kentucky Plumbers Twitter Feed | Plumbing Videos


                      • #12
                        Re: Combustion Air

                        I would follow the manufactures recommendations on the piping if they suggest a trap I would put in a trap,

                        And as Dunbar said condensation can collect and destroy your investment. Which is cheaper, a tee and drain line or a new combustion chamber or blower?

                        Most codes will defer to the manufacturers installation instructions with some exceptions to accommodate local conditions such as anticipated snowfall, placement near windows or other openings, proximity to other utilities or services, local preference for screens on pipe ends, etc. You will also find that exhausting into a walkway or onto a deck area where people (especially young ones) can be exposed to fumes is not allowed.



                        UCC Codes for PA

                        From the PA state website:
                        "The Commonwealth of Pennsylvania currently has no licensure or certification requirements for most construction contractors (or their employees)."

                        In other words, you are totally on your own when finding a competent contractor. Licensing and/or certification does in no way guarantee you'll get a knowledgeable contractor, but it does weed out the total FUs and most of the shysters. How many references for this contractor did you check before you signed the contract? apparently not enough.

                        If this is a gas fired appliance then you need to see the Fuel Gas Code book too.
                        Last edited by Bob D.; 11-11-2010, 06:17 AM.
                        "It's a table saw, do you know where your fingers are?" Bob D. 2006



                        1/20/2017 - The Beginning of a new Error


                        • #13
                          Re: Combustion Air

                          Thank you guys. The manufacturers guide definitively specified a trap on the Combustion air intake line NOT the exhaust. In the case of the exhaust it described pitching the line so that condensation would drain back into the furnace by design. There is a combustion condensation drain system exiting to my condensation pump which carries off condensation back draining in through exhaust as well as condensation creating during combustion. Again it appears that this how Rheem designed it.
                          Regarding the combustion air intake, since they specified a trap, they are probably not expecting water to enter the furnace air intake (as will with the exhaust ). The question is will the air intake collect any water unlike the exhaust.
                          There is no grill recommended if you add risers on the outside wall as I have extended them to about 40 inches (allowed 60), only if you exit straight out. I believe what you're saying BHD and I will research grills. It does say do not install on the prevailing wind side of the house, and i am good there.
                          It is now according to manufacturer spec I believe now, except for the trap in intake. This installer supposedly had the best reputation of the 2-3 I talked to. It is possible he see's nothing wrong with the PVC installation? I did have them back once to pitch it and they admitted it should have been pitched. I also know for a fact that they install ton of these. And I believe the fully modulating furnace design is a few years old now.

                          Oh a closer look at the manual says in lieu of a grill on an installation of the combustion air pipe (inlet) they provided a piece of PVC vane to be cemented vertically inside the end of the intake termination. I saw the vane on the top of the furnace and had no idea what it was so i left it there. Since the time I saw it they came back and shortened the exhaust pipe to pitch it and now I don't see the piece? I guess I'll fashion something from PVC.

                          I feel that the installer was neat and did a reasonable job of adapting the installation to the environment (challenging), however they neglected a few very important details which were easy to do, not pitching the pipes and not installing the inlet vane piece or a trap. I intend to tell them so. Thanks
                          Last edited by claudius2k; 11-16-2010, 09:22 PM. Reason: Update


                          • #14
                            Re: Combustion Air

                            Guys, it says no screens allowed I believe right on the picture he posted. Also, an accelerator is advised on the exhaust to get the gasses away from the side of the home (and utilities) Go from 2" to 1 1/2" at the final horizontal piece if the TEL (total equivalent length) allows. An elbow gives you 5' of linear length right away plus the actual pipe.

                            I'm a lennox guy and they say the same things. If the 2" pvc was pushing it and does not allow you to "goose neck" up high enough, you'll get intermittent Pressure switch faults.

                            Unlike one guy said, no one will get killed, I promise. You will however get nuisance failures.


                            • #15
                              Re: Combustion Air

                              Thanks rjm. I didn't think it was that dangerous as long as there are no indoor leaks and no one can stand near the exhaust by accident. I have it about 3-4 feet from the ground. It is conceivable (every 15-20 years we'll get a snow storm with 4 feet on the ground or some drifting. But very rare. I'll just have to keep it clear if that ever happens.
                              Interestingly the manual recommends a vertical piece of PVC be inserted in the intake across the opening sticking out about 1/2 inch. They call it a vane and I think they suggest it to eliminate any spiraling air flowing across the intake as it obstructs wind flying by the opening. It should keep birds out also. I am certain if I added screening it would freeze up. 3-4 snows so far so good.