Looking to buy a new heat pump to replace my current heat pump which is about 20 years old. Got a quote on a new one with a seer rating of 15, plumbed to my water heater. Does hooking it to the water heater really help or is this just a sale pitch? Also want to know if going to a unit with a 16 seer rating with a 2 speed compressor is worth the extra money? Plan on being in this home for at least 10 more years. Thanks for any info.