Water tank is on the way out, apparently my wife told me this a week ago, I can't recall. Filled the tub for a bath for the boy and before getting half way full it was cold. I can't say how old it is but definitely 15+. Before I run down to HD/or Blowes and buy a plug in replacement (nat. gas) should I consider any thing else like an on demand water heater? I'm all in for efficiency but not for blowing a beer budget on champagne taste.