Does a washing machine drain need a vent?

Answer: In most cases
Explanation: While we perform HVAC services, not plumbing services, we often need to tap into a drain line, and have to stay up on codes for plumbing and electrical as well, to ensure everything we install is up to code in our area. As for the need to have a vent for a washing machine drain, most building codes require a vent for a washer drain. Even if your local code doesn't require it, it's still a good idea to have one. It eliminates the possibility of your washing machine not draining properly due a vacuum being created.

Answer: In some cases
Explanation: if you have a P-trap no, but an air gap mechanism is required by some municipalities