The disadvantage of tankless is that you may not have enough hot water to supply multiple simultaneous uses (running 3 showers at a time, for example). So what I'm thinking is a tankless and a tank heater feeding into a mixing valve such as a Watts LFMMV. Set the tankless to deliver 110F and the tank to deliver 120F and set the mixing valve to supply 110F. Then under normal conditions the the mixing valve calls for "cold water" of 110F from the tankless but if the tankless can't keep up and falls below 110F then the mixing valve mixes in hot water from the tank to maintain the 110F. Would this work?

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

I can remember back in the late 50s and early 60Âs when fuel was cheap the water heaters were operated at 180degF and they had no insulation or external jacketing. In those days there was a great concern that people were accidentally bumping up against the water heaters and receiving severe burns. The standards were then amended requiring that all water heaters must have a minimum of ¾" of fiberglass insulation, a sheet metal jacket and under no circumstance could the external temperature of the unit exceed 140degF under normal operation. During the first fuel crisis in the mid 70Âs people were encouraged to install additional insulation blankets to reduce the standby losses from the water heater, however it was soon realized that if an insulation blanket is improperly installed it interferes with the normal function of the water heater thermostats and temperature & pressure relief valves causing very erratic temperatures and in some instances creating safety issues. In addition, quite often when the insulation blankets are improperly installed they interfere with the normal flow of combustion air and result in very high levels of carbon monoxide. In the late 80Âs the plumbing codes were again amended requiring that ALL water heaters must now have a minimum of R-12 insulation. REF: International Residential Code IRC-504.2.1(en) Uniform Plumbing Code UPC-150(j)1A(c ) The codes specifically sayÂ"No external blankets required" Many local codes have amended that wording to say "External Blankets Prohibited". In my jurisdiction there is a $50 fine for even selling a water heater blanket. In order to meet the new insulation standards most water heater manufacturers have discontinued the use of fiberglass insulation and they now use cast in foam insulations, which often far exceed the required R-12 minimum Everyone seems to be fixated on the supposed high energy wasted to standby losses from a tank type water heater, but in reality such is not the case. Two years ago our plumbing apprenticeship class, in co-operation with the local gas company and a number of local hardware stores, appliance dealers and plumbing suppliers set up a project to test the actual cost of water heater standby losses. Twelve different makes and models of residential contractor grade 50gal gas tank type water heaters were installed in an unheated warehouse. All 12 units were fed from a common water line and each water heater is supplied through a separate gas meter. Each water heater is then fitted with one line on the output side that terminates into a keyless hose bib beside the unit, thus there is no demand from these water heaters therefore they represent standby losses only. The water heaters were then filled and left standing with the thermostats set at the code maximum of 120degF. Every month the gas meters are read and the fuel cost is computed at the standard residential rate for this area. After two years of following this project it has been determined that the monthly average standby loss is $5.02. (The worst case in the test is averaging $5.87mo.) I might add that two of the water heaters in this test have specific wording in their installation manuals that states the addition of an insulation blanket will void the warranty.

Wow, 6+ showers! Do 6+ people take showers at the same time? In other words evaluate how much hot water you need in a particular time period. Anyway, we have recirc system. Rather than use the built in timer, I use X-10 devices to control the pump. We turn it on a few minutes ahead of use at a particular point of use then turn it off (unless it is the dishwasher or clothes washer which run for longer periods of time.) The downside is that one has to time how long it takes for hot water to reach the various points of use . There are other remote control technologies such as Insteon, Z-Wave, etc. If you don't have the return line available, there are pumps that use the cold line as a return that are usually installed at the farthest point..