If you vent into your attic check to see if you have PVC stack pipes. If so, and if you are handy, you can cut out a section and install a Y-connection and attach your exhaust line directly to your stack pipe and your exhaust will not build up in your attic and instead be exhausted directly outside.
 
Another thing that can be done to try to mask heat buildup in an attic is to run a long exhaust line that snakes back and forth across/around all or most of the attic space. You seal off what would normally be the exhaust end of the line and poke/punch small holes all along the exhaust line so the heat is dissipated over the broadest possible area so if a heat signature were taken it would appear to be more natural, as in normal built up heat from the sun, and not a hot spot in one area of the attic.
 
Another option is depending on what sort of vents your attic has you can run an exhaust line directly to a vent or better yet if you have a full ridge vent. The heat will escape quickly with minimal buildup. The main problem with either of the last two options is if you are in a winter climate and enough heat will build up to melt snow that would build up on your roof and not melt because of attic insulation. A bare spot on an otherwise snow-covered roof can draw attention. If your home is under insulated and if you are in a winter snow area the snow will melt off anyway so some additional heat will not create a situation that stands out like a three legged race horse.
 
One other option is going down through the floor if you have a crawl space. Because of possible odor buildup a carbon filter would be a very good idea in such a case because meter readers, service workers of some type or another who may be needed to repair a pipe or heat pump heat exchange or something under your home or other types of workers like people who spray homes, including under homes, for termites and other bugs might catch a whiff and figure out what is up and possibly rat you out or tell you to share your crop with them in exchange for keeping their mouth shut or even one day pay you an unannounced visit of a hostile nature and abscond with your crop. Some or all of that might seem to be somewhat far fetched but over the decades I have heard of just about any imaginable unwanted scenario happening.