via Jim Allhiser
Here are just some of the things that well meaning installers can get totally wrong:
Flue issues: This is absolutely important with gas appliances. If you don't get the flue right you can allow carbon monoxide to freely enter your home. This particular flue was built out of vinyl dryer ducting. The plastic had been melting into a puddle on the top of the tank.
This is this home owners solution for the flue exhaust. The home owner may have thought that a clothes dryer and a gas fired water heater were basicly the same thing.
Here is a picture of the draft hood in action. Notice the lighter's flame tipped away from the hood. This means that flue gases, instead of going outside, are coming inside! This is potentially a deadly setup that has apparently been in place for years.
These are just some of the many things that can be done wrong by a less-than-handy handy person.