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Drawing combustion air from elevator shaft?

pilusopiluso Member Posts: 44

I recently moved to a new house. The HVAC unit was working during warm days but did not fire during cold days.

Two contractors saw the unit and they agree that the exhaust pipe is too small for the unit and distance to the outside.

The unit is 100,000 BTU and the pipe travels around 29 feet with a few angles. The installed pipe is 2" in diameter
and according to the manufacturer's specification it should be 3". Picture attached

The first suggestion to fix the problem was to install a new pipe. This is not easy becaust I will have to open up the ceiling
in two rooms and the unit is on the fourth floor making it very difficult to access the outside vent, which is on the side of the house.

The other suggestion was to connect the exhaust and intake pipes with a Y and draw combustion air from the room. The Y would
enlarge the capacity of the exhaust pipe. The problem is that the HVAC is in a closet in the laundry room which is relatively
small. One contractor suggested drawing combustion air from the elevator shaft that is behind the closet, very close to the
HVAC unit.

My question is, is it ok to draw combustion air from the elevator shaft? Would the Y system work? Any other alternatives
about drawing combustion air without going outside? Should I just look into enlarging the exhaust pipe?



  • Tim McElwainTim McElwain Member Posts: 4,012
    I would say you cannot get air from the elevator shaft. However check with your local code officials to be sure.
  • SlamDunkSlamDunk Member Posts: 345
    Seems to me that when elevator went up, it would suck air away.
  • JUGHNEJUGHNE Member Posts: 4,170
    edited March 13
    Considering the difficulty with the 3" install, I would try something else first.
    I had a borderline exhaust issue with pressure switches not closing.
    I took the 2" tee right at the furnace, replaced it with a DWV tee and rotated it 90 degrees.
    The exhaust went straight thru the run of the tee and the drain was connected to the bottom branch. The branch of the tee was installed to drain the cond of the main exhaust pipe before it could go back to the fan.

    Then out of the run of the tee with a 90 or street 90 (DWV) go up and eliminate the double 45's which actually add a 90 in the run.

    This helped tremendously for my situation.
    The air coming out of the fan had been running into the back of the square turn tee (in effect a non radius 90) and created air flow resistance immediately.

    It would be worth a try given the alternative, IMO.

    What does your outside terminations look like?
  • unclejohnunclejohn Member Posts: 1,187
    That is a lot of heat for a condo. It might be easier to take out the 100K and replace it with a 80K. Then you can go 55' equiv.
  • pilusopiluso Member Posts: 44
    This is very helpful. Thanks a lot. I really want to avoid the 3" install. I'm not sure I follow all your steps but will talk to my contractor. I might try to draw out what you suggest to see if I got the idea. In the meantime, I'm attaching a picture of the terminations.
    It is a borderline exhaust issue. The neighbors have the same or similar install with no issues.
    Thanks again
  • ratioratio Member Posts: 1,298
    Think about what @unclejohn said. It's quite possible, perhaps even likely, that the current unit is oversized. A correctly-sized unit would solve your flue sizing issues handily and save you from the grief that often accompanies oversized equipment.
  • JUGHNEJUGHNE Member Posts: 4,170
    Those terminations look challenging to say the least.
    They look close enough for rebreathing of exhaust back into combustion.
    Why an odd number of 5? Do you have a power vented water heater?

    My son had issues with his condo furnace.
    He had water stains on the bedroom ceiling, while visiting I watched the furnace operation.
    The exhaust would spit out drops of water for a while then suddenly it would belch out about 2 cups of water.
    There were some serious icicles hanging from his exhaust, a pile of ice on top of the AC directly under the exhaust.
    He had bad glue joints leaking and sagging pipes running about 15' horizontally above the bedroom ceiling.
    He called the original installer who came out and cut the ceiling open, fixed the bad joints and (hopefully) corrected the sagging.
    He also hired sheetrock finisher who did a great job of blending in a textured ceiling.
    HVAC installer covered all expenses.
    He had subbed out part of the install to some "git er done" company. This was not the only bad install in the complex he had to eat.

    So hopefully your ceilings are dry and no major ice hanging outside.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 3,689
    Are you thinking of taking combustion air from the inside and using both existing 2" pipes for exhaust?
  • CanuckerCanucker Member Posts: 391
    edited March 14
    > @SlamDunk said:
    > Seems to me that when elevator went up, it would suck air away.

    I don't think the elevator is that tight to the walls. Probably a heck of a stack effect in that shaft though. Good draft numbers, maybe? ;)
    You can have it good, fast or cheap. Pick two
  • ratioratio Member Posts: 1,298
    From my experience, they often are that close to the wall. I know at least one elevator that I could persuade to grind on the shaft wall merely by standing in one certain spot, and and a high-rise freight elevator will announce it's approach by pressurizing the shaft, which will blow out around the doors.

    Hmmm, yes, I forgot about that. Unless you want the flames to point OUT of the burner whenever the car is moving away from the intake, you don't want to take air from there. OTOH, when the car is moving TOWARDS the intake you wouldn't need an inducer...

  • pilusopiluso Member Posts: 44
    Thanks for all the good ideas. I agree that the unit the builder installed is oversized. I think that's the root of the problem. However, I'm not thinking about replacing it for now, it is only 6 years old but it would be a solution.
    The terminations are very challenging which is a problem for installing a 3" pipe.
    The original idea was to draw air from the inside of the house, the best would be the elevator shaft if it makes sense. The unit is also next to a hallway, so that could be an option. It is in a small laundry room with a water heater. So I think I need to get air somewhere else. Correct?
    I would then use the 2 2" pipes for the exhaust. Does this make sense?
    I'm also going to see if we can follow what Jughne suggested, at least getting rid of that first angle might help.
    Thanks again

  • IronmanIronman Member Posts: 4,105
    edited March 14
    The mechanical code forbids running duct, flue piping, venting, etc. in an elevator shaft.

    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • JUGHNEJUGHNE Member Posts: 4,170
    There could be lack of adequate combustion air in your unit.
    You mention laundry room....clothes drier pulls a lot of air out of the building and it sounds close to your furnace room.
    What do you have for water heater? If gas and not having 2 pipes if it is power vented, then the same negative air issue.
    Kitchen and bath fans also are competing for free air.

    IIWM, I would try the exhaust piping change I mentioned.
    I was amazed for the difference it made....something like a factor from 1.0 to 1.33 for pressure improvement.

    The neighbors units could be closer to the outside walls and possibly have smaller units. They would look the same from the outside....need to check the rating labels inside the furnace.
  • pilusopiluso Member Posts: 44
    Thanks Ironman for the info
    Jughne I tried drawing out what you suggest to see if I got the idea. I'm attaching it. Is it correct?
    Many thanks

  • JUGHNEJUGHNE Member Posts: 4,170
    That is what I was thinking. DWV fittings have more curved corners than the pressure type with square corners.
    The branch of the tee has a curve to it also. I put it such to allow any water draining back down the exhaust to smoothly flow into the drain.
    Then adjust the length of the pipe between the tee and 90 to line up with the existing vertical pipe. Eliminating the 2 45 ells.
  • pilusopiluso Member Posts: 44
    Great. I will try it. It might be a few days but I'll let you know how it goes. Thanks
  • pilusopiluso Member Posts: 44
    One question, what do you use to connect the drain to the bottom of the branch? Thanks
  • ratioratio Member Posts: 1,298
    Glue-in -> threaded reducers. You might be able to do it in one step, but it can be built up via a number of fittings too. Is there actually a drain on the bottom of the tee? I can't tell from the pic.

    Also, there are long radius (aka sweep) 90's that should be used when you turn up, they are less restrictive than the normal ones. You may need to get them from a plumbing supply house, I don't believe the big box stores around here carry them.

  • pilusopiluso Member Posts: 44
    Yes. There is a drain on the bottom of the tee. It is small and connected with a little hose to the furnace. That's why i was wondering if there is a special piece I need to get. Reducers should work. I will look for the long radius 90s. Seem like a good idea. Thanks
  • DZoroDZoro Member Posts: 263
    The reason it didn't work in the cold was due to frost/freeze up at your venting terminations. Your intake sucked in all the exhaust gasses from the pipes next to it. Looks like the whole building should be corrected.
    What does the inside of that unit look like?
    The furnace won't last long with that venting arrangement. It's sucking in exhaust gasses during the warm weather also.
    If your going to try re piping use 3" at the furnace as far as you can then reduce to 2" . Re pipe terminations properly.
  • GBartGBart Member Posts: 56
    Do you all realize you are talking to the homeowner and not a contractor?
  • GBartGBart Member Posts: 56
    Take the model number of your Payne unit and download the installation manual, in it it tells you exactly how TO and HOW NOT to install the piping. Any deviation is never guaranteed to work, EVER, you may need to get the builder, building inspector involved if this is a new home.

  • pilusopiluso Member Posts: 44
    I am the homeowner. But i will be running all the suggestions by the builder and if that doesn't work a contractor. Will not do it myself but it's been the coldest months wihout a solution. That's why i decided to investgate options.
  • GBartGBart Member Posts: 56
    That's what I meant, if this is a new home there should be some kind of warranty. Download the manual, it has the layout for the piping, that was designed by the manufacturers engineers as to what WILL work, if they didn't follow that it probably won't, that is what you show them and the building inspector, everything up above in comments is speculation.
  • pilusopiluso Member Posts: 44
    In response to Dennis comment, a contractor suggested connecting the inlet and exhaust pipe with a Y and then trying to draw air from inside the house. Would that be a better solution?

    Again, I agree that the builder messed this up. I think it was an honest mistake but a mistake anyway that he needs to fix. Short of redoing everything there might be simpler solutions that might be worth trying.

  • GBartGBart Member Posts: 56
    Is it a Payne PG95XA?
  • pilusopiluso Member Posts: 44
    it is a Payne PG9YAB
  • GBartGBart Member Posts: 56
    The manual has almost 100 pages and several almost 20 dedicated to vent line sizing and layout, you can almost double the length of the exposed pipe by simply insulating it, you can go to a larger diameter. You really should follow the manual for all units.
  • pilusopiluso Member Posts: 44
    By the way, the manual says that it should have been a 3" pipe and I called Payne and they confirmed. But they also said it was right at the limit, borderline.
  • unclejohnunclejohn Member Posts: 1,187
    You should not need a drain on the ex. pipe. Those units are design to drain back into the furnace and out the trap. The ex piping should be pitched towards the furnace for this purpose. In fact if it is not that could be part of the problem.
  • pilusopiluso Member Posts: 44
    It has one now. I'm attaching a picture of the current installation. By the way, thanks for all the comments. Very much appreciated.

  • ZmanZman Member Posts: 3,900
    As for your first question, No, absolutely nothing in the elevator shaft but the elevator and supporting equipment. The mech code forbids it and the elevator inspector will red tag the whole elevator.

    I agree with the comments about the terminations. The whole building is done incorrectly and it will eventually damage everyone's furnace. Perhaps the HOA should bring this to the attention of the builder and the building inspectors. Sure the builder and contractor made a mistake. Their mistake left you and all the other owners with no manufactures warranty. They need to fix their mistakes.

    If you decide to let the builder off and accept having no warranty on your furnace, you could probably disable the second stage on the furnace and never know the difference from a comfort point of view. My guess is that occasionally the second stage calls on cold days and that is when the undersized vent becomes an issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • pilusopiluso Member Posts: 44
    Isn't disabling the second stage dangerous? One contractor suggested that but said it could be dangerous
  • GBartGBart Member Posts: 56
    If you disable the second stage you are cutting your max btu output in half, you may not heat on a cold day.

    Zman is correct, if a unit is installed wrong there is no warranty or factory support. Although when I was a factory rep at Carrier/Bryant/Payne we did help people or get a pro to straighten it out, at 6 years though, I don't know, how did this work in years prior is the real question.
  • GBartGBart Member Posts: 56
    If this worked for 4-5 years and now gives issues there could be something in the pipe, bugs, nest, who knows, just enough to cause an issue, if it was installed wrong it should have been an issue every winter.
  • pilusopiluso Member Posts: 44
    We are in Philadelphia. The previous owners spent the worse months of the winters in Florida. It works when it is not very cold. I'm not that worried about the warranty because it has already been almost 7 years.
    They checked the pipes but they are ok. I'm going to suggest to the builder trying to fix the pipes. It seems that the last resort would be to replace the unit with a smaller one. Would that work?
  • GBartGBart Member Posts: 56
    You would have to get a contractor to do a heat/cool load calculation and find out the actual btu's required, could be that is the correct unit, could be it's over sized, can't do that on the internet or over the phone.

    The vent pipes have to be according to the factory installation manual which you say you have. It could be as simple as the piping that is exposed to outdoor temps needs to be insulated, for example on a Payne PG95XA 2 1/2" vent pipe has a max run of 50ft for non insulated and 80ft with 3/8" insulation, it's all in the charts.Then you have limits for maximum equivalent vent length for fittings, etc etc, it has to all be laid out and followed, otherwise you're shooting in the dark and making guesses.
  • pilusopiluso Member Posts: 44
    Points well taken. Will look at the chart and talk to the builder about insulation.
  • JUGHNEJUGHNE Member Posts: 4,170
    I am not familiar with that family of furnaces.
    But the Nortek line always starts out on high fire regardless of what stage is calling. After 5-10 seconds it switches down to low fire.

    You are on the 4th floor, are there any floors above you?
    If not, could your pipes could be in a cold attic?

    The odd number and 2 sizes (Three 2" and two 3") of terminations is somewhat baffling. On a cold day do you see "smoke" vapor coming from all of them?

    How many square feet is your home?
    How many outside walls?
    A lot of glass?
  • pilusopiluso Member Posts: 44
    It is a duplex, 2 floors and 2 floors. We are on the top 2 floors. It is around 1600 sqrt feet. Front and back are windows. Sides are other apartments. No attic but above us there is a roof deck that's why they put the vents to the side, I guess. I don't know about all the terminations but there is a water heater in the laundry room with the furnace. Then there is a bathroom. I know that one of the terminations is for the bathroom fan. I don't know about the smoke. I will check.
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