Benton,

Tankless, point-of-use, instantaneous - whatever term the salesrep uses - are difficult to apply well in a retro-fit to a typical upper MidWest house. I'm neither for or against them, but do some hard homework before deciding. I'm on the regulatory side of the business, and we open-mindedly see everything under the sun; what works and what doesn't work. Some things to look into:

1. What is the water temperature of your water supply in the dead of winter? We have VERY cold supply water in my town (Mississippi River source) in wintertime; as a practical matter yours can't be colder (but probably isn't warmer) and that has an unbelievable impact on how much hot water you can wring out of those puppies. You need to review ALL the rate-of-rise data and size for the largest winter time situation - usually showering. Here (south of you) the size required at least doubles from summer to winter conditions.

2. The efficiency information is usually over-hyped and you need to read the fine print. At full output they require an enormous energy input. At trickle-of-warm water rates (like shaving), most of them are fairly inefficient. Heat exchanger design is optimized for certain conditions, and the device's automatic energy controls vary from "off-or-on" to some number of discrete steps or levels, depending on the specific model. They simply cannot be universally efficient through a large range of demand situations.

3. The best way to take advantage of these is to put one at every point-of-use location - every shower/tub, every lavatory, etc. That's a heck of a lot simpler to do with a new house as it's being built than with a retrofit to an exisiting house. There are many compromises made when they are used as a substitute for a storage water heater in a house that was designed for a storage water heater.

4. In an efficiency flat with a shower/tub, lavatory, and kitchen sink all on a common wall or plumbing chase, located within a few feet of each other, they make a great deal of sense. In a flat with pay-as-you-go energy metering, they make sense from the landlord's point of view. They are very difficult to adapt to typical Western lifestyles, especially USA lifestyles in typical USA houses unless you put lots of properly-sized units all over the house. And you will NOT recover those costs in increased efficiency over a normal lifetime if you do it that way. Even extra-high efficiency storage tank heaters take a while to pay back the increased cost - the math is simple; check yourself.

If you want to really make a huge dent in your home energy use (assuming your home is reasonably well insulated and draft-sealed already), look into ground source heat pumps. If you choose, they can also provide all your domestic hotwater needs, and the industry in the US is finally mature. They eliminated the big problem (choice of anti-freeze for the working fluid) some time back, so take any apocryphal stories that armchair experts may relate to you with a grain of salt. The upfront costs on a re-fit are scary as heck - we're talking home equity loan here for most folks - but the return-on-investment times are typically extremely short unless you have unusual geological circumstances (BEDROCK). It's almost absurd that new homes are not nearly universally built with ground source heat pumps in this area - especially in new subdivisions, when a common well field can be installed very economically on a per-house basis.

OK; this is ETS and I'm simply not going to add any more to this thread or any other home-improvement stuff, Campfire forum or not.

I hope this is food for thought, and helpful to you.

Tom