My gas water heater corroded through and was leaking, of course it was Saturday afternoon. I removed the old one and went to Home Depot on Sunday morning. I explained my situation to the sales person in the plumbing department and was recomended a straight replacement for the unit I had. I took it home spent a few hours plumbing it in. By supper we had hot water again. To be on the safe side I phoned union gas to come and inspect. The technician arrived and commented on the good job of the water and gas plumbing but as he looked up he said, "you won't be happy about this". The chimney that I had been using for years was no longer legal for this application (things change). The external 'b' vent was no longer allowed. My only option was to go to either an on demand water heater of a power vent water heater. Home depot would not take the installed unit back and I had a time limit from Union gas to correct the situation. I had to get in a plumber to install a new power vent water heater and there were no takers anywhere in the used market for the water heater. Total cost $2700 for replacing one gas water heater. The "used" water heater went to habitat for humanity where they can install a chimney that can use this type of water heater. Since many home owners would be in this situation when replacing their older water heaters Home Depot should be making the consumer aware that a straight replacement may not be legal. This law changed in 2004. Old water heaters in use do not need to be changed over but any replacement must bring the installation up to the new standards.