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Baffled, Anyone heard of this?

Shane_2 Member Posts: 192
Customer called- CO detector had gone off. Over a number of days. At odd times.

Small office building. One of two CO detectors were replaced due to age, possible malfunction. New detector and separate one had alarmed.

Hot water supplied by standard chimney vented 40 gallon gas water heater. Chimney clear and seems in pretty good shape. Vent proper size (4").

We are the third company to this party this year.

Went through building at different times on two separate days.

CO readings were 3-7 PPM through out building, even in mechanical room.

Only time we get a reading is next to lavatory with hot water running. 50-80 PPM.

Anyone have any suggestions? What would cause a CO reading on hot water?

Water heater is 2014, installed by one of the other companies.

Thank You


  • JStar
    JStar Member Posts: 2,752
    Could air from a drain/waste line be leaking into the space? Sewage will set off CO alarms.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,545
    Water vapor can trigger it. NYS code requires a CO detector on every floor but they can't be installed in kitchen,boiler room,garage or bathroom
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Shane_2
    Shane_2 Member Posts: 192
    Looked for leaks/crack blocked plumbing vent in DWV, it's old but couldn't find an issue. CO detectors are mounted about 20' away from bathroom or break room (kitchen sink).

    Still can't figure out why we would get readings(with our portable tester) on the hot water only. 50-80 PPM.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,545
    Is the bathroom fan wired into light? Need to check draft on HWH in a worst case scenario ie. all doors and windows shut and any potential mechanical sources of negative pressure running
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • 4Johnpipe
    4Johnpipe Member Posts: 483
    edited July 2015
    Have they ever had their water tested. We had a rather big issue with poly water mains and a gasoline spill from old tanks. It prompted a study on the permeability of poly water pipe. Not sure if that would set of a CO detector, however you would smell it in the water...
    Considerate People, Considerate Service, Consider It Done!
    email: langansph@yahoo.com
  • clammy
    clammy Member Posts: 3,113
    i think you should look at the labatory exhaust hoods and any other exhaust systems also check and see if any of the hoods are equipted with provisions for make up air ,chk the building for negative pressure pulling a possible back draft on your chimney .Even though you may have enough sq in the room where the hw heater is located it does not mean you have proper combustion air for all conditions that the unit may operate on ,nepressure in building with labatories is a tough one if theres no make up air system ,some times buildings with package roof tops and ecomizers mask the promblems till it either to hot or to cold out and they close to there miniun postions .Take a look atthe the manaul ecomizers and powered ones some one may have either closed them or dis abled them due to no heat or no cooling calls under heavy loads .If this building has drop cielings make sure that any power roof ventalaors are not in run away mode.Ona side note if you find that there is no make up air and plan on changing pulleys and suchg on lab hoods do urself a favor and get aspeed controller for thge hoods they cost more then changing pulls but allow you to crank down those exhaust fans to balance there air flow alot of times i ve seen the make up undersized for the exhaust ,building with pleum returns and ecomized usually make it difficult to pin piont peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Lance
    Lance Member Posts: 273
    Just did a survey for cooling in master bedroom. House appears to be a flipper project. Found the basement lavatory exhaust fan duct venting into the chimney with the furnace, also the furnace main return air duct was in the same room as the draft diverters. Many other flaws found, but gas stoves and ovens need adjusting as well as any combustion device. Make them test zero PPM and if CO still present in the air, you will know to look elsewhere.
    Good luck.