As far as a water heater is concerned, there are two types of pipes that can be installed on water heaters. Coppers and rust-resistant steels are the metallic types. PB and CPVC are the most predominant types of plastic pipes.

Plumbing Connections

When examining a water heater's plumbing pipes for trouble, look for any rusting at the threads on the hot and cold lines on top of the water heater. Also look at the T&P valve's plastic pipe, if it has one, for any wear and tear. Your T&P valve can be found on the side of the water heater and can be activated by lifting a small metal clip on top of it.

If you have copper plumbing, its best to use copper flex connectors on the hot and cold lines above the water heater. Make sure that adapters with plastic-lined nipples are installed directly on the hot and cold ports themselves. The flex connectors can be screwed directly into the plastic-lined nipples themselves and also heat traps can be installed here to increase heating efficiency by a plumber. The hot water line may have a combination anode rod attached to it inside the water heater. The cold water line will have a dip tube attached to it inside the water heater. If you install a highly recommended curved dip tube, use plastic-lined nipples. Three inches is the minimum length.

If you have steel plumbing, its best to use plastic-lined nipples connecting at the hot and cold ports on top of the water heater and two more plastic-lined nipples connecting into the wall. Use copper flex connectors to connect between the appropriate lines.

There are adapters which can be used to adapt between PB or CPVC to metal pipes. Long flex connectors may also attach to these adapters.

Insulated Plumbing

To increase the heat efficiency of your plumbing, install 3/4 inch insulation on your hot and cold lines on your water heater. Keep the insulation 3 inches away from the water itself. Be sure to get the right insulation for the right sized pipes. Both galvanized pipes and copper pipes aren't actually the same size even though they may both say they are 3/4 inches.

Don't insulate the metal tin draft diverter above a gas water heater. Its the large metal duct that acts like a chimney flue for your water heater. Don't cover fittings or unions on the plumbing either. You may need easy access for them later.

Whatever the insulation you decide to use, follow the instructions for installation. If you're not sure what to do still, buy some heavy duty gas wrap tape or plastic zip ties to hold the insulation in place.

Problems With Oversized Plumbing

If your installing new plumbing, be sure to use pipes that are no larger than what is necessary. Large pipes have larger surface area from which to lose heat from for heated water. Water can more easily sit inside the oversized pipes and freeze as well.