Product review (5 stars): Heartland Dryer Vent
I have lap siding (Hardi Plank cement boards) with a 5 inch reveal.  To mount the base of the dryer I put down a thick bead of silicon caulk on the siding where the square base would be positioned and then fastened the base with the enclosed screws at the four corners of the base.  I pre-drilled the holes into the cement siding.  I used the caulk to make sure I had an air tight seal.  I let the base and caulk set for 24 hours and then placed the vent top with the floating valve into the base, removed the cap, and turned on the dryer to check the seal.  The floating valve shot right up out of the base almost 2 feet into the air, so I felt confident that the seal around the base was air tight and all the exhaust air from the dryer was coming out of the vent.  I fastened the top of the vent to the siding with the enclosed screw, again pre-drilling the hole in the the cement siding.  When the cap is in place the cap directs the exhaust air downward and that keeps the floating valve from shooting out of the top of the vent.  The vent works just as advertised, sealing up nicely when the dryer is off.  I noted that some lint tends to accumulate between the lip of the vent top and the cap, so when I check the insides of the vent for cleaning by removing the cap, I will be careful to scrape around the lip of the vent where the cap fits and keep that area lint-free.  Overall a great product, fairly easy installation (especially if you don't have lap siding to contend with), and a lot better design than the normal dryer vent with the plastic hinged vanes that open when the dryer is on and close (somewhat) when it is off.  We had a mouse get inside the normal dryer vent and it died there, so that was not a good thing.  The Heartland vent will prevent that from happening and provide a positive seal against the outside air.