Negative air pressure?

Discussion in 'HVAC Heating & Cooling' started by vtxdude, Nov 30, 2009.

  1. vtxdude

    vtxdude New Member

    Messages:
    127
    Location:
    NH
    When my furnace is running it is creating a draft that is strong enough to close my cellar door if I close it to about and inch or so...the systems is a Lennox 26-21-1 and is a high efficiency furnace

    The draft is so strong that it is sucking cold air down my water heater flue and if the WH comes on it is not allowing the exhaust to go up flue and it spills all over my basement


    What can be done about this???? Anything??? Should a plumber be able to determine what needs to be done?

    I am hitting roadbloacks where ever I go...do I need a powervent heater? will this solve issue for exhaust?
  2. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Combustion air

    Your cellar must be tight. Sounds like you need to provide some combustion makeup air for the furnace in the immediate area of the furnace.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,258
    Location:
    New England
    What you're seeing is a reason the newer, higher efficiency units have closed combustion...i.e., they bring their own combustion air in from outside. A combustion device will draw air from the easiest path. It can be quite dangerous if you don't have enough fresh air to any combustion device. You may need to run a fresh air vent into the area around the furnace from outside. You'd probably want to put a damper on it so it wouldn't leak cold air all the time. If you have a gas clothes dryer or stove also running at the same time, you could run into even bigger problems.

    If you have the instructions for the furnace, it will discuss the minimum size of the room where the heater is, and how much air it needs.
  4. biffnh

    biffnh New Member

    Messages:
    27
    Location:
    Squam Lake, New Hampshire
    Get yourself a CAS (combustion air supply) unit for your boiler. They are easy to install, make tremendous sense, AND the boiler run much more quietly! I didn't expect this bonus, but I can't believe how it quieted the running. The unit has a draft controller that will open should something happen to block the outside air.
    I purchased mine from Patriot Supply (a marvelous company) for $118.00. This is a must in the newer tight homes.
  5. veesubotee

    veesubotee New Member

    Messages:
    11
    I had a situation similar to yours. Air was flowing rapidly under the door to the basement.

    I determined that I had a rather large leak in my return system. I made a simple tool using a dowel (about a yard long) with a 1" strip of facial tissue attached to one end.

    By running the tissue over every seam and connection, I was able to find many leaks that were not apparent on first inspection. Pay particular attention to concealed areas, as this is where many installers take short cuts.

    Such was my situation. A section of panning had a vertical section to the main return trunk (below). The connection was short by 1/2" and ran across the trunk (22"); a considerable leak.

    Since the trunk was virtually on the ceiling, there was no way to repair the connection. I used a section of (cold) water pipe insulation, which has a cut along its length, and jammed it (opened) into the void. Problem solved.

    Using the same method, I determined that air was being sucked into my Aprilaire filter (new) via the bottom of the door. I called Aprilaire (thought I could get a new door. Lots of luck with that.). I used a section of the pipe insulation and slid it into the space between the door and the floor. No more leak.

    V
    Last edited: Dec 1, 2009
  6. Ian Gills

    Ian Gills Senior Robin Hood Guy

    Messages:
    2,777
    Location:
    USA
    I wish I had a tight house so I could worry about such issues.

    The only air I get coming under the basement door in my 1950s rambler is from outside.

    I spent so much money and time insulating, weatherstripping and changing the windows.

    Then the new HVAC guy comes round and ticks the box "loose".

    Could be worse I suppose. There is a "very loose" category you know.

    I'd sure like to meet her!
    Last edited: Dec 1, 2009
  7. vtxdude

    vtxdude New Member

    Messages:
    127
    Location:
    NH
    HVAC guys came and determined that my furnace was starving for air the 2 cold air returns downstairs were just 2 small slits maybe a foot long and a little over an inch wide. The opened up the duct work on 1 end and made the return longer and added a 12X12 grate...also open up some duct work near the dining room return to about 4 inches

    What diff it has made for airflow...I had to replace my brand new filter it was so filthy after running it for like 5 minutes!

    No more negative pressure
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Thank you very much for getting back to us to explain the resolution of your problem.

    This was one of those cases where we knew something was not right, but not being there, we could not pin it down for you.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,258
    Location:
    New England
    Your water heater will probably vent better now, too.
  10. vtxdude

    vtxdude New Member

    Messages:
    127
    Location:
    NH

    It does, I can have both running now without the spillage but it still has that bad whatever smell it is after running maybe 5 minutes or so




    :(


  11. BINGO


    I bet your old water heater had been backdrafting in that cellar the entire time, and the new one basically sent off warning flags to you because you could smell the burnoff of the flue chase, plus a possibly higher btu burner.

    You are on the right track, I mentioned that water heater wasn't to blame, but Sears is now because they incorrectly installed a water heater without doing a draft test to clarify it was operating properly. It falls back on them for sending idiots to do the job.


    If that furnace was installed in recent months, the furnace guys should of done a draft test on the connecting flue pipes to see if it was overpowering a lesser fixture.


    Answer this question YES OR NO:


    Did the water heater that came out, was it blackened/rusted/burned up heavily on top of the water heater...

    or

    Did it look like the day it was installed, still had the paint on the metal covering, everything looked normal?
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,258
    Location:
    New England
    New combustion devices often smell for the first bit or so as the oils, paint, etc. bits of volatile compounds burn off those areas that get hot. It may all be fine in a little while longer. New ductwork could have a little oil or dust on it that will outgas as it 'burns' in.

    How long that takes, I'm not sure...haven't had that many new applicance installed, and, most of mine have sealed combustion, so wouldn't notice anyway.
  13. vtxdude

    vtxdude New Member

    Messages:
    127
    Location:
    NH
    Dunbar...to be honest everything looked fine on top of the old water heater....I don't know what it looked like that day it was installed as it was here when I bought the place but I do know that the top looked ok..nothing like you are asking


    It is a complete mystery on the smell...the only thing I can think of is they 2nd plumbers put foil tape all over the seams where the pipes connected..the HVAC guys pulled it off and instead put fire resistant caulking on the seams......at first I thought it was the adhesive from the tape burning off but not so sure now...it has been a few weeks and I still get what I consider a combustion smell maybe 5 minutes after heater kicks in..I don't get it...smell is just as strong today as back then....


    JAD/Jim you should come by and I'll show you exactly what I'm dealing with and you might even have some ideas....I'm right up DW highway and also right off Exit 11


    I have been looking through the manual and comparing what I have found to what is in the trouble shooting...flame is a bit lazy...sometimes it is blue with orange points..other times it is a lot yellow...some soot marks on draft hood...loud burner noise......lots of pinging and creaking in tank....and of course the smell


    I am stumped...if it is a secondary air issue my only option is a fan in a can I think they are called...I am not keen at all about piping in 10 below NH winter air if I understand how they work......and then what if that doesn't solve it? I have had my door open which is allowing all sorts of cold fresh air in and that doesn't seem to solve the issue


    It must have something to do with new more efficient water heaters vs ones 20 years old



    Could it be the design of the Sears water heater where it gets it's air from the slots underneath and with that mesh like screen on the bottom vs a Bradford white that has the vents on the side maybe allowing better secondary air flow?


    When gas company was here today he stuck his meter in the flue for CO and it got as high as 60ppm than started to come down...he said that is fine as the probe was right in the flue...not sure if that means anything in relation to the venting of the heater



    So all that to say..the old water heater did not have a scorched hood...I don't remember that Vanguard giving my 1 once of trouble in 8 years until the day I came home and the TP valve was leaking all over...then everything has been a mess since


    Electric is probably not the smartest thing to do but it would solve this issue thats for sure
    Last edited: Dec 13, 2009
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