Here goes: We currently have a 40 gallon natural gas water heater on the south side of basement two feet from chimney flue. All the hot water requirements are on the north side of the house, 30' away. We were given by our neighbor, who upgraded to a 80 gallon power vent, a 40 gallon power vent water heater. I would like to install the power vent on the north side next to the hot water requirements. Then I had a brain storm or headache, can't remember! "What if I intalled them in series?" With two teenagers the wife is always... unhappy because of no hot water when the two teenagers are done. The basement is 30'x30'x7'. Is this possible? Would I put them in series or parallel? Can the power vent be vented vertically? The plan would be leave the original where it sits on the south side.

I don't see any problem with it. You would definitely want to do it in parallel at that distance. Basically just tie in the cold supply to the nearest 3/4 cold water pipe, and the hot to the nearest 3/4 hot pipe. Of couse, you will need to get gas to it, and yes, you can vent a power vent vetically, but it would be easier to just take it out a rim joist. Or, you could install the new heater next to the old heater and install a recirc line and pump (which is what I would suggest). This would give you immediate hot water and pretty much endless hot water(80 gallons goes a long ways). If you put the new heater on the other side of the house, you may get a bit of a temp fluxuation for the first minute or so while the hot water from the old tank reaches the fixture in use. So basically, the new tank will get hot water to the fixture, but it will be mixing with cold water from the old heater until the hot water from the old heater get there. The way I see it, you would have your temp set, then all of a sudden the water at the fixture would get hotter. Make sense?

The water heater that was given to me is a AO Smith Power-House Power-Shot. I would like to use an old, unused, unlined chimney on the north side of the house. What is the maximum number of feet that the pvc can run? How much do I add for elbows? I was planning on four feet horizontal in basement with two elbows, up the old chimney around 25'. How do I terminate it? Is this too long of a run? What about condensation? Our houses are close in proximity, less than four feet. Our house sits almost on top of our property line on the north side. I really like our neighbors so I don't want to upset them with a exhaust pipe. Thanks for your help. In addition our neighbor with the upgrade the plumber ran a hot water "loop' to the third floor but not the second floor. The kids have instant hot water and the parents have to wait. I laughed.

As far as the venting specifics go, you will have to get your hands on an install guide for that exact water heater. You may be able to run the pvc vent up the chimney, make a cap for the chimney and terminate according to instructions. I would ask the neighbors if they would be bothered by an exhaust out the side of your home. That really would be the best way to do it.

Running it up the chimney would most likely creat a condensation issue, but in the install instructions, they should have the info on how to deal with that by adding a drain tee near the heater.

Ok, total input BTU is 80,000 on both units. Will I need to upgrade my 1/2" gas line? What is the reason for an expansion tank on the cold water line? Where I live there are no meters, backflow valve, just tap at main then the water valve at street. Will I need the expansion valve, would it be beneficial?

!/2 would most likely work, but it depends on the length. Safe bet would be to increase to 3/4 and supply each with half.

As for the expansion tank, if you don't have any pressure reducing valve, check valves (backflow preventers) or the like, and your house pressure is less than 80psi, then you won't need the expansion tank. The expansion tank merely keeps the water heater pressure relief valve from popping off due to water expanding when it heats up, but if you don't have a backflow preventer of any kind, then the expansion tank really isn't needed. However, it wouldn't hurt a thing to install one anyway, but I wouldn't worry about it.