I am getting a project done which includes a tankless water heater. I dealt with a salesman and was trying to tell him I wanted to be sure my heater had a little tank in it. I was referring to the buffer tank (navien) and wanted to be sure the model 210ang meant it had it. That is the model I am getting, but he didn't know enough about it (I think) so he wrote for a 15 gal expansion tank. He didn't raise the price for it so I figure it can't hurt. Is there any reason to get exp tank or not to, since at this point it is included and I won't get $ back if I don't get it.

I would prefer to have a recirc line put in. I think the navien has a pump built in for it. How much would the recirc cost? I was hoping I could "trade" the exp tank for the water line....but I read that it has to come from the last faucet. I don't know which one that is, but I have a 2 story house and the heater is in the basement. If these are copper lines then I assume it will be a lot if the last faucet is on second floor...I have 2.5 baths and also the washing machine is upstairs. .How do I figure out which is last? Any thoughts on prices? I am in high priced NJ.

Also, is this something another plumber (a neighbor) could do later if I decide I really want it?