We have a second stackable electric dyer on the first floor that is vented via a Y vent connection from our primary gas dryer in the basement. The electric dryer actually gets warm when the gas dryer runs. Is there any danger of carbon monoxide escaping into the house thru the electric dryer vent?
Any backpressure or restriction in the dryer vent duct beyond the wye piece will cause backdrafting into the house via the second dryer vent in your situation. Given that a gas dryer is blowing combustion exhaust out its vent, this is a bad situation, especially considering that lint-induced dryer duct restrictions are inevitable. In order to solve this, you'll need to give the electric dryer its own vent or replace it with a condensing dryer, preferably a heat pump model. (IMC 504.10 and 504.11 require a continuous or interlocked exhaust booster fan of the appropriate type, but are not intended to be used in a SFR context where the required maintenance cannot be guaranteed.)