The old water heater has no expansion tank, and thus is leaking out of the t&p valve every time it heats cold water up to temperature. We are getting roughly 80 psi from the street, which is the max safe pressure for most residential plumbing. When the water heater recovers after a shower, its skyrocketing to 140 psi until someone opens a faucet. An expansion tank is required to prevent this. It contains a pressurized rubber bladder which allows the expanding water a place to go. Plumbing code didn't require one when this tank was installed.
The other, bigger problem is that it is installed under the house in a location that only gives 48" to the bottom of the floor joists. A large water heater will simply not fit. Armed with my measuring tape, I checked in the tallest location under the house, in a foundation corner. I had roughly 68" in this location - enough for the 80-gallon unit I was looking at (plus piping). Since electric heaters typically have twice the recovery time of a gas unit, I made up for this with more capacity. Two smaller water heaters is another option, but is more expensive.
I started out by digging out the clay in the new location to put in some concrete blocks for a stable base. Leveling would have been easier with the addition of some gravel, but I did not feel like making a trip just to pick some up.
Next I planned out the piping around the heater. Our house has copper pipe, which is relatively easy to work with using sweat fittings. I've found its best to do as much soldering as possible in a well-lit, comfortable workshop, rather than in a crawl space.
So I am building sections as units to avoid soldering as much as possible under the house.
The t&p valve on this tank is located on the heater top, so a pipe is run with an elbow to eject any discharge water safely to the floor.
I made sure to attach dielectric unions to tank inlet/outlet nipples since they are galvanized steel and the house pipe is copper. Without them the unions would quickly corrode due to the galvanic reaction between the dissimilar metals. The dielectric unions have plastic bushings and a rubber washer which electrically isolate the joined pipes.
A little plumber's dope on the union seals the joint when I tighten it to the tank nipples with a pipe wrench. I was pleased that the tank came with heat-block fittings already installed, which prevents heated water from wafting into the pipes when idle.
The new water heater on it's pad. This was a beast to get down there, it weighs roughly 125 lbs empty. It should weigh about 800 lbs full. The expansion tank came precharged to 25psi. After measuring our water pressure (and finding it to be 80 psi, holy crap thats high!) I charged the expansion tank to the same with my air compressor. This is the max the tank can safely take.
I hung two pipes back to to the old water heater location, using copper-coated steel wire hangers. All in all, its about 60 feet of 3/4" diameter copper pipe. There is only one 90-degree direction change in the pipes.
I drained the old heater by attaching a garden hose to the drain fitting.
I had to drain it into a few buckets since the water heater sits below the outside soil level. The valve kept clogging from sediment in the tank. I switched back and forth between emptying these buckets. It was slow-going since its draining from gravity only. Once the tank was drained I cut the cold/hot pipes with a hacksaw and spliced the new pipes into the house plumbing system.
Off of the cold supply union I have installed two ball valves to provide shutoff capability to the heater as well as isolate the expansion tank if it needs service. Ball valves are considerably more reliable than gate valves, open and close with only a 90-degree turn, and it is much easier to to tell if they are on or off.
Once I cut over to the new heater I had two leaks from poor solder joints. They were the first two that I did :) The first I had to cut out to drain the pipe properly. It is not possible to solder a pipe full of water. The second I was able to drain easily and I just added more flux and re-sweated the fitting. I use a MAPP gas torch instead of propane, to solder fittings. MAPP costs several times more than propane but heats much faster, and is worth every penny.
The last step was to wire the 30-amp 220V circuit to the new heater. This was easy since the new heater is next to where the circuit enters the crawlspace.
The problem with running a longer hot water pipe is heat lag on faucets. The time is takes to get hot water to the faucet is a nuisance and waste of money. I plan on over-insulating the hot water pipe back to the original feed, and adding extra to the the branch pipes. Once a faucet has been used for hot water, the water in the pipes will stay warm for longer.
For the cold feed I plan on using cheap polyethylene foam insulation, since I am only need to prevent freezing in the winter. For the hot side I used the more expensive foam rubber insulation, and I plan on adding a layer of fiberglass batting as well.
In the future I am going to add a pressure reducing valve to the house cold supply so I can dial down the pressure a bit. This will make our appliances, faucets, fittings, expansion tank, and water heater last longer.
