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Orphaned Water heaters

Mark Hunt
Mark Hunt Member Posts: 4,909
Went on a call this morning for a customer that has had problems with condensation putting his pilot light out on his water heater. At least that is what the other company told him.

He has a 50 gal. atmospheric draft water heater that vents into B-vent that was dropped down the exterior masonry chimney. The forced air furnace was replaced with a sealed combustion high efficiency unit in 1993, leaving the water heater alone in the B-vent.

The customer replaced the old water heater in April and has had problems ever since.

I performed a "worst case depressurization" by running exhaust fans, clothes dryer, and furnace blower.

The basement went down to -3.5 pa and the flue gasses from the WH came right out into the basement. The WH was only producing 25ppm of CO but that could change in an instant. We will be replacing the water heater with a power vented unit next week.

The point is that no-one knew to check for this depressurization problem. The draft problem had nothing to do with "combustion air" or an unlined chimney. It had everything to do with high pressure going to low pressure, always.
And the leaky duct system sitting right there next to the WH sucking the CO into the return duct.

If you don't test, you don't know.

Mark H

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  • Earthfire
    Earthfire Member Posts: 543

    Once again a curios mind and experience strikes.The other guy forgot rule # 1 If it goes out IT must come in . That building needs a fresh air intake that can satisfy the needs of the dryer exhaust, kitchen and bath exhaust fans, furnaces, heaters, fireplaces, and any other air consuming appliances, especially the people. They consume oxygen and produce exhaust gasses of warying quantity and Quality ( METHANE?)
  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    Right you are.

    When we do blower door testing in homes, folks are amazed at where that "make up" air is coming from.

    Nothing like some good ole fibre glass from the attic or some fresh mold from the basement not to mention the other stuff that's floating around.

    Most heating appliance manufacturers give a good description of this test in their install manuals(pilot lighting devices)


    Mark H

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  • Mark I am curious...

    was this happening with the old water heater that was replaced or did this just start? It seems to me that this may have started when the furnace was replaced. Just a thought. By the way the test you performed is in the National Fuel Gas Code as a suggested method for testing equipment for adequate air. I tell technicains to do this check on every service call.... just might be why the pilot keeps going out on that equipment. Hmmmmm It should be done even if your math says you have sufficient air. I also have a troubleshooting guide on Air For Combustion that instructs on things you need to check for reasons pilots go out related to air.

    One I remember was the pilot on a water heater was out every Saturday morning. A little detective work and we discovered the reason was that every Friday night this family had family night. They played board games and had pizza AND LIT THE FIREPLACE. The fireplace was creating such a change in pressure that the flue on the water heater was reversed and spilling, this caused the pilot to go out. By then providing make up air adequate to overcome the difference in pressure and isolating the water heater the problem went away.
  • mp1969
    mp1969 Member Posts: 226
    flue exhaust problem

    Great Topic,
    We used to use a simple match to verify updraft in chimneys and other venting , worked fine when homes had all sorts of infiltration.
    Since we have tightened up our homes with insulation ,house wrap and started using sealed combustion units for furnaces we often overlook that old atmospheric water heater and think it runs ok in an oversized chiney or long (tall) "B" vent. this can and has been a problem if proper outside air in new homes is not provided or oversized chimneys are not downsized to meet the decreased load for the often only used water heater.
    I use a mirror to check for obstructions (broken flue ,debris or dead birds etc. then I use the seven times rule (figure the cross sectional area of the appliance vent piping and the cross sectional area of the chimney it dumps into then divide the chimney area by the appliance vent area, if the number exceeds 7 you need a chimney liner.
    Also many gas appliances dump into chimneys with no tile flue or liner, this creates a situation where the acidic flue gases attack the mortor joints and can lead to chimney crumbling and possible partial failure.

    Great topic evolving from our usual trial and error way of solving problems when we introduce new products or concepts.

    MP 1969
  • Wayco Wayne
    Wayco Wayne Member Posts: 615
    Could someone

    describe the test please.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    The "worst case depressurization" test I do goes like this.

    1) Close all windows and doors to simulate a winter time condition.

    2) Using a digital manometer, run one vinyl tube to the outside of the house and attach it to the "reference" port on the manometer.

    3) Take a base pressure reading of the "combustion appliance zone" or CAZ with NOTHING running and that includes air handling devices.

    4) Once you have the base pressure, start turning exhaust fans on, and note the change if any. Turn on clothes dryers and air handling devices and note changes if any.

    BPI protocol dictates that the lowest allowable pressure in a CAZ for an orphaned atmospheric water heater is -2 pascals.

    The attachment has some of the protocols for the Energy Star Program and we follow them on EVERY job.

    Mark H

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  • Mike Kraft
    Mike Kraft Member Posts: 406
    Excellent Thread Mark............

    And you deserve a major award:).Thanks for thinking and thanks for the information.

  • Another way if you do not have...

    test instruments:

    1. Close all windows and doors, make sure the fireplace damper is closed. You are trying to create as close as possible the tightest condition the house can experience.

    2. Bring on every exhaust fan in the house, bathroom, range hood, attic exhaust even though it may not be used in the winter and ALSO THE DRYER.

    3. Start to bring on the equipment in the house that burns any kind of fuel gas or oil.

    4. With everything running check with a match at the draft hoods of every appliance that has one. If the match is blowing back at you there is a negative pressure in the building.

    5. Corrective measures must now be taken to bring in outside air (make up air) equal to what is being removed.

    6. A note of caution here..... you may also have to bring in additional air for combustion for the appliances.

  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    Excellent point Timmie!!!!

    And things can change quickly!!!

    I've mentioned this example before but it bears repeating.

    Test a top burner on a gas stove. Hold your analyzer about 8" above the flame. You'll probably see a spike of CO and then it should drop off.

    Now put a pot of cold water on the burner and test again. You'll be amazed at the readings!!!!

    There are some companies that tell there customers that gas appliances don't need to be serviced every year like oil appliances because gas burns cleaner. B.S

    And I know of no-one in my area that even gives water heaters a second glance and they certainly don't include them in their "yearly preventative maintenance" programs.

    The Energy Star program here in NY is teaching contractors to understand cause and effect. The window/insulation contractors are testing to make sure that they don't leave houses in dangerous conditions after they do their work.

    Lower energy bills don't mean a thing to sick or dead people. The health and safety of our customers is job one. Our customers expect us to know about these things.

    Thanks Timmie!!!

    Mark H

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  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    Thank you Cheese!!

    If I could pick the major award, I want the leg lamp!!!

    Mark H

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
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