Position the new heater so your piping--particularly a gas vent pipe--will reach most easily.
Install the heater's new draft hood (gas heater). Many have legs that insert into holes on the heater's top (Fig. 4).
Every gas water heater needs proper venting that's no smaller than the draft hood collar of the new heater. It's a good idea to use new vent pipe elbows, as the old ones will probably be corroded at their present angles. The vent should go straight up as far as possible. Then any horizontal run should slope upward at least 1/4 inch per foot, as shown in Fig. 5.
Connect the vent pipe with short sheet metal screws (Fig. 6).
Now you can make the hot and cold water connections. The easiest way often is using copper flex-connectors, available from your dealer. Figure 7 shows how flex-connectors fit a heater's female tapping (left side), or male stub (right side). At the upper end, the flex connectors make up to a threaded metal pipe (left) and a sweat-soldered copper tube (right) using a male adapter. They range in length from 12 to 24 inches--the 18- and 24-inch lengths being most practical. Flex-connectors are easily bent to reach where you wish.
How the hot water piping is handled depends on whther your house has threaded metal, sweat-soldered coper, or thermoplastic piping, and whether it is 3/4 inch or 1/2 inch. No matter what, though, the old heater should be fitted with a cold water gate valve (Fig. 8). To keep it from becoming sediment-fouled, the valve should be placed in a vertical section of piping.
Use Teflon tape (but not pipe dope) on the male threads entering flex-connectors. If your water heater has female-threaded tappings, you'll need a pair of short 3/4 inch nipples to accept the flex-connectors at the bottom. If the heater comes with 3/4-inch male-threaded stubs, the nipples are not needed. At the top, the flex-connectors fit directly to the ends of threaded pipes (or a male adapter sweat-soldered to copper tubing). Some install to copper tubing without sweat-soldering, an advantage. If you sweat-solder, be sure to do this before installing the flex-connectors, as the heat from soldering would damage the connector gaskets.
Thermoplastic pipe. Flex-connectors are not necessary with
CPVC or PB plastic pipe. Needed are what's called "transition unions"
to go between the metal heater threads and the plastic piping.
Some manufacturers of plastic fittings also call for the use of foot-long
threaded steel nipples between the water heater and the transition unions
to distance them from conducted burner heat. Two more transition
unions are needed at the top end where the plastic risers will join the threaded metal water lines (not required if your house is plumbed with plastic tubing). You can use rigid CPVC tubing, solvent welding the joints. Or use flexible PB, joining with mechanical couplings (Fig. 9). PB cannot be solvent welded. And don't try to hook up a water heater with PVC, PE, or ABS plastic piping, as these will not take hot water.
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