Water Heaters - Water Heater [& furnace combind] Vent problem

We have a powered vent Trane furnace. Our installer ran an insulated chimney liner all the way to the roof and put on the appropriate cap. The Water heater was reconnected to that line as it was with the old furnace via a Y connection. Furnave 6" line Water Heater 3" going into an 8" insulated flue.

Only when the furnace is on does some of the exhaust vent back into the basement through the water heater flue. If the furnace is off the heater vents itself perfectly.

Unfortunately the water heater pipe runs with very little upward pitch to the flue Y connection from a 90 degree elbow on top of the water heater. There is currently no physical way to change this. There is a CO detector with digital reading in the same room and never reads any CO, but the humidity that it puts into the basement is a problem.

Any suggestions?

Thanks

Have you called the installer ?? They should handling this not you.

Check the specs from your water heater manufacturer, but they may require a minimum 45º angle; no horizontal. That elbow on top of your WH also causes too much backpressure,, and you could have trouble with the burner staying on.

Bottom line: (a) Verify that both the furnace and WH flue installation complies with manufacturer's specs.
(b) Has your inspector signed off on the whole thing yet?

Hello: kfech

Very likely the combined flue is undersized for the set up, distance and exhaust volume. Also, that 90 degree elbow is all wrong. Cannot have an such angles in any vent pipe that is not power vented and sealed. Exhaust fumes will spill back into the room, as you say they are.

And fumes are doing so (backing up and spilling) as evident by the moisture and humidity noticed. The venting system is not correct. Must be changed.

Not likely any or enough CO is being produced to cause an alarm to activate. A clean burning flame, correctly adjusted with sufficient air for combustion, produces little carbon monoxides. Thus will have little or no effect on the alarm, if it is working correctly. Likely is but do not replie on it.

Recommendations:
Get the venting system problems corrected asap and inspected by local city inspector and the gas supply utility rep. Correct that water heaters venting system asap and have a licensed contractor do the work or call back the original installer and have that person (company) do the work correctly.

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