We don't want to shut off the water when the remodel to the room is finished. We just want to switch the water source . For example after finishing the hall bath, can water coming from the water heater in the attic be switched via the remodel process to the new tankless water heater that will not be in the attic? But still will need the old water heater for rooms not yet remodeled and whose plumbing hasn't been upgraded to copper,etc. Can both water heaters be running at same time? For example keeping the master bath and the kitchen still using the water heater in the attic because plumbing will not be complete yet that routes them to tankless. So we will have both tankless not in the attic and the old water heater in the attic working at the same time but just servicing different rooms. Can we do that? I didn't specify since I'm not a plumber but I can't help thinking that main issue is that you need gas going to both water heaters and water from the outside being routed into both water heaters. Not sure if this is possible to do. Then after 6 months or a year when all rooms are remodeled and have their galvanized pipes replaced with copper, etc. and have plumbing routed to new location of tankless, the old water heater in the attic can be shut down because it won't be used.

There isn't an exact answer to your question, it will vary by how hard the water is, and how much you use. What they are doing (or should be doing) is removing the lime buildup in the heater with vinegar. The acid will dissolve the hard water deposits that will eventually clog a tankless. It's about a 10-15 minute flush with vinegar. You can google it and see many videos on how to do it. Three years is about right in your situation. I wouldn't just let it go. Tankless heaters use small heating coils to expose the water to heat quickly. You don't want those passages to clog. You can call around for a good price over the phone. They don't need to come out to give you a quote, this is a basic job.

Guys if you read the post, the reason the tank water heater was so expensive was due to the construction required to get his house up to code. I personally like my tank heater. If your changing from a tank to tankless there is alot of work to do. Moving water lines, moving gas lines (possibly upgrading gas line size too) and running a new intake/exhaust if using gas, upgrading the main service amps if using electric. Some things to consider Tank Heater Pros Costs less to replace in the future Easier to maintain (Tank water heaters are easy to flush out every year) Easier to install (dont have to upgrade gas line or main service amps) Gas water heater will still operate in power outage (electric will still have some hot water to use for a while till power kicks back on). Cons Not as efficient as tankless No Tax Credits Hot water limited by FHR (first hour rating) Tankless Heater Pros Unlimited hot water More efficient Saves space Cons Will cost more in the future to replace (there is no guarantee the tankless will last longer than a tank version, the heat exchanger can go bad and that is the most expensive part of the tankless) , Harder to maintain (you need to try to clean those tankless heaters out every year with a descaler so they stay working efficiently) Harder to install (upgrade gas line or main service amps) Tankless heaters have a limited throughoutput. While it is unlimited hot water, it can only supply so many gallons of hot water at a time Will not operate in a power outage. A tankless water heater is controlled by electronics whether the heater is gas or electric does not matter. Requires minimum gallons per minute from city water supply, some people have not been able to install due to that problem. Consumer reports note that users complain of inconsistant water temperatures. http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm Another good site to look at: http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/tankless-water-heaters.html

So, @For M1, This sounds like a very bad plan. Don't go into a tankless replacement/install without some good planning. Just don't. 1. How hard is your water? Get a hach test kit and find out. Don't guess. 2. Do not buy a "Generic Chinese HWH from Ebay" there's lots of ways that can go wrong. You have no way of knowing it's been certified by various safety agencies including the gas part, the electrical part, lead free, etc. Not to mention warranty or service. 3. You need to know the approximate temp of the cold water in the winter and how much hot water you would use at one time. For example, do two people get ready for work at the same time (two showers). 4. You need to know the BTU input for the water heater. Then you must determine if you have adequate gas supply to the heater - and to the house in total. Don't guess. 5. You must adhere to venting requirements. No creativity here. Otherwise you will go to sleep and not wake up. This is not standard DIY stuff, and I get the impression that you are inclined to guess / take shortcuts / look for cheap hacks. This isn't the project to do that with.