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.

Combustion Air intake condensation

Peterug13 Member Posts: 8
Good evening. I have a Slant Fin LX-120 mod con. It’s firing fine and working great in so far as heating the house. However I noticed some condensation dripping from around the air intake. The intake is not piped to outside but draws air from the basement. There is about an 18” rise of 3” pvc from the top of the boiler, a 90 and about 5’ of straight pipe and C another 90 pointed down. Looking at the boiler info it is acceptable to pull room air. I’m concerned because I pulled the intake pipe from the boiler and there is condensation all the way down into the boiler where it connects to the blower. The open end of the vent is in a part of the basement I never go in so it’s possible it’s ajj K ways done it and I never noticed but…..

The last service was in March of last year and there was no mention of any issues. 


    EBEBRATT-Ed Member Posts: 15,516
    if the condensation is dripping into the burner compartment then i would be concerned. if not it's probably not an issue.

    is the area the air is pulled from warmer or cooler than the boiler location?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,822
    Condensation forms based on the temperature and humidity of the air. If the parts of the boiler are relatively cold in comparison to the amount of humidity the air contains, condensation will form. So one thing comes to mind, Is it possible that an unvented clothes dryer is operating in the basement resulting in ultra high humidity in the basement air? Or any other source of humidity? fish tank, indoor swimming pool, hot tub or spa, if not, then we need more information about the boiler location and its surroundings.

    Another source of condensation could be a leaking exhaust vent. This is a safety issue. Gasses from category 4 appliances have a high amount of humidity in the exhaust, if those gasses leak out of the exhaust pipe they will most likely have condensation as part of the leaking exhaust gasses bur more important is those gasses could also contain Carbon Monoxide, and you don't want that.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Peterug13
    Peterug13 Member Posts: 8
    The basement is rather humid normally. 200
    year old New England basement kind of humid. It has rained a lot recently and we do have problems with water seepage when it does rain. I was concerned about the possibility of CO but haven’t had any alarms.

    To answer EBEBRATT as far as I could see in both directions the inside wall of the pipe was sweating right down into the intake of the blower fan.