they have vent like that made for a furnace it's stronger than the flexible type for dryers.(which i would not use on a dryer because of the lint factor)

it's been like that but for peace of mind you might want to have the building inspector check it out.

i do see a lot of that type of pipe on furnaces nowadays though.

Thanks, I thought it was ok because the length was at least 15 ft or more, but I might replace themm because I've had to duct tape it all over the place. Thanks, Sue