Basically, there are two types of transition hoses available to purchase and install between the dryer and the in-the-wall exhaust system. Namely, the wire bound foil flex and the semi-rigid aluminum flex. As a safety note, absolutely do not use the white vinyl spiral bound flex as it is very unsafe and prohibited by most building codes and appliance manufacturers.
Of the two popular transition hoses, there are some pros and cons that apply to each one. The foil flex exhibits awesome stretch to compression ratio and is very easy to work with but is strongly discouraged by the appliance manufacturers due to its inability to contain a fire. It also exhibits extreme airflow restriction due to the rough walls and that the material folds, or collapses, within the interior actually decreasing the inside diameter of the opening. The semi-rigid aluminum flex is harder to work with but is required by the appliance manufacturers. It maintains the full four inch inside diameter and exhibits a rather smooth interior, much safer and much more energy efficient than the wire bound flex.
When installing the aluminum flex, here are a few tips. If your hose did not come with pre-prepared ends, the installation can be much easier if you roll the first two inches of the flex flat with an object similar to rolling pin. Here, we are using a two inch piece of PVC pipe. With pressure, you can flatten those ridges in the duct. You can also cut three slits in the end with scissors and open up the mouth a bit more. A neat trick is to take pliers and create two very small hook-like protrusions in the pipe's end. Once you tighten the hose clamp, this small catch will make it much more difficult for the flex to slide off the rigid pipe which is actually a very common nuisance.
If you have the model 350 Dryerbox, the one with the oval hole, it can be a concern in getting the round transition hose flex over the very oval shape of the rigid pipe that penetrates the Dryerbox. To be clear, there does not exist a fitting or an adapter for this. The flex transition hose will fit over the oval pipe, and the trick is to prepare the pipe like we discussed earlier and then to squeeze or deform the flex similar to how you would grip a large hamburger. Remove any sharp burrs and simply work the open end up, on and over the rigid pipe.
The worm style drive hose clamp is the most appropriate means to clamp down and secure the flex to the rigid pipe. Make sure you tug on the flex to confirm that it will not dislodge as you move the dryer back into place.
With the wire bound foil flex, again, the trick is to remove any burrs on the rigid pipe and squeeze the flex to mimic the shape of the oval pipe. The worm drive clamp will conform to the oval shape. Hopefully, these tips will assist with your dryer installation.
Over two million dryerboxes are installed in homes throughout the country. There are four new construction models and two retro-fit models. The latter are available from Amazon and Lowe's, while the new construction boxes are available from over two thousand heating and air conditioning outlets.