Quick question, can we vent two dryers thru one 4" rigid vent pipe? Thank you!!
No you can't hook them up together because of the hazard of backdraft, overheating, fire and moisture.
Depending on local and state codes, you may be able to only if you use a back draft preventer----but even then it may not pass code or inspection.
The only time you can absolutely connect more than one dryer to a common vent is when that vent is properly engineered for the airflow. For example, in apartments.
Here is a link that might be useful: Example of enginneered venting
That's a helpful link... Even for commercial they recommend separately venting each one, or going up to at least 8" on the main line...