Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Draft on cold boiler

STEAM DOCTOR
STEAM DOCTOR Member Posts: 2,210
in Gas Heating
General question. What sort of draft numbers should be expected on cold flue/boiler? Purpose of such a test is to determine if there are negative pressure issues in boiler room/building. Thank you.

Comments

  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Draft

    If you mechanical room is positive you will have a slight draft in the chimney, even with a cold boiler, but this is not the norm.  Most mechanical rooms are negative unless some type of mechanical fan is running during the off cycle.  The important question is what is it during the on cycle.  Without some type of mechancal combustion air fan the room is still going to be slightly negative.  The question becomes is whether or not the flue can overcome it.
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,210
    Numbers

    What would be considered negative enough to indicate excessive negative pressure in building?TY
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,210
    neg pressure

    What I really want to know is what is the best way to determine (using a combustion tester) if there is an unsafe negative pressure situation in a building.
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Negative pressure

    An unsafe negative pressure would be one that doesn't allow the boiler to start venting within a few minutes.  To determine if an appliance is venting with a combustion analyzer(which is the only way it can be verified) is to watch the O2 and CO readings.  If they are stable after 3 minutes (could still be going down slightly, but never up) you are venting.  If they start to rise after they bottomed out you have a venting problem.
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,210
    ?

    If the numbers go up how do does one know conclusively that there is a negative pressure issue in the building as opposed to some other CO causing issue
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    venting problem

    You look at the draft reading after several minutes.  If it is -.02" or higher you do not have a negative pressure problem, but if it is lower you do.

    If the draft is -.02" or higher and the CO is rising that is an equipment venting problem.
  • VictoriaEnergy
    VictoriaEnergy Member Posts: 126
    Test Standard

    I believe the certification standard for Cat I appliances mandates successful establishment of draft from stone cold start-up with the mechanical room being depressurized to 10 Pascals, about .04"WC



    I've known this for a long time & can't remember where I learned it from or who told me.  May have been HVI. 

    There was an error rendering this rich post.

This discussion has been closed.

Categories