The CBW will vent moisture laden air which may include some chemical residual. Many exhaust fans have been installed in CBW vent systems but if the fan impeller is inside the duct it is exposed to the vapors. In addition, condensate forms in the duct and runs down the bottom or side of the duct and drips onto or into areas that may be problematic.
We also had reports of a steam valve failure in a CBW module cause the meltdown of an expensive plastic fan blower and housing. So, be aware that the vapor can be as hot as steam (about 212 degrees or possibly more).
Ventilation fans can be pricey. And, they tend to fail early since they are always in a horrible environment. Motors coupled to the fan and through the fan housing are susceptible to drips and vapor which may cause early failure. Corrosion is to be expected. Drips of condensate are normal if not considered at design time. Metal fan housings will be exposed to corrosive condensate.
There are companies that design and build venturi inducers that uncouple the fan from the vapor laden duct. The prices are high but may provide long service life. An example can be found here...
https://www.quickdraft.com/capabilities/venturi-powered-systems/
Saint Gobain exhaust fans with Plastic housings have been used but experienced some meltdown and dripping issues. Also consider that the fan housing will collect condensate and need to be drained. The drain may not work until the fan is turned off due to the negative pressure in the housing. Many users simply open the vents on the CBW and let the vapor rise to be handled by the laundry exhaust fans. This normally works fine unless you have an air conditioned space or low headroom and a general lack of room ventilation.
Be cautious with piping the back of the CBW to the front in a common duct. Vapor of acid and oxidizer can mix and create very corrosive condensate. Milnor recommends a 2 part system, isolating the last mod vapor from the oxidizing zone vapor.
Be careful with horizontal vent runs as they collect condensate and drip. Be careful not to let the duct drip onto the stainless CBW top as when the condensate evaporates the remains could be corrosive. PVC pipes tend to sag over time as the temperature softens the plastic. So, every system has its downside. Make the best decision for your specific system and environment to eliminate long term problems.
The venting plan from Milnor is attached. Be sure to check for current any updates in the installation manual.
