Hi Greenie100, Great questions. The answer between the two choices probably involves how much water your family uses(including habits) and how much insolation you get in your OR climate. I would guess the bigger system. I have used the Marathon tanks and love them. The biggest selling point to me is that they have no anode rod to change out which is usually the death of most tank water heaters. Dont take a DIY installation lightly. If you have skill with copper plumbing then it can be a great way to save some money but be prepared for lots of time and tinkering if you have no experience with solar hot water. Be very careful about how you install your backup tank and monitoring for expected performance is crucial. Dont skimp on controls and thermometers. The bottom link is troublesome for me to include because I dont necessarily agree with all of the authors points. It is however getting tougher and tougher to spec solar hot water these days due to the incredible efficiency of heat pump water heaters and falling prices of PV. I feel Solar Hot Water still has its place but it is making less financial sense these days. Here is a link that might be useful: Green Building Advisor article; Solar Thermal is Dead

I put one in last year, and according to my kill-a-watt meter, we're paying less than $10 a month for hot water even at our summer electricity pricing, which is 22 cents/kw. That said, the heart of the technology is basically the same as a $99 window air-conditioner, and the new units are made in China - so who knows what the durability will be. I paid $699 shipped, but apparently, these units were selling for $499 before the tax credit was announced, and it looks like the price was recently jacked to $799... The quality seems decent, but it does have a "buzzy" sound when it's running that would be really annoying if you had it near a sleeping or living area. The install was super-easy for me - I used a new AOSmith 50-gallon electric water heater as the tank (I hooked up the power supply to the standard heater, but turned off the breaker, so I can use the standard elements if the Airtap fails) Would I do it again? - MEH..I dunno - playing around with the pricing to steal the tax credit seems kind of sleazy, the warranty is really ambiguous - to qualify for the tax credit they had to offer a five-year warranty I believe, but their website now says two years - the new integrated units from GE and Rheem have ten years of coverage, and they have the benefit of being able to use both the heat pump and standard electric elements to give you super-fast recovery if you have guests over, or a huge garden tub to fill. A quick Ebay search shows the competitors are around $1500~ish, but if you haven't taken the tax credit yet, you could snag $500 in government cheese and nullify the cost difference with a better warranty. The technology is an excellent idea, and when the competition drives pricing to where it really belongs - (Until then... meh... Certainly it can pencil out, but the energy-saving payoff exceeds the warranty which makes me nervous. Solar really isn't any better, and tankless seems to be snake-oil when you look for real savings data, but to each his own...

I installed it all and plumbed it myself - Not a really difficult job . . . . maybe 3 on a scale of 5 The collector panel was $1K, the tanks were $600 for the pair, the circulator pump was $100, the differential controller was $200 and about another $300 for copper piping, valves, flowmeter and an analog temp guage. $2200 for the total system, give or take $100. We had no hot water heater to begin with, so we would have had to spend $300 anyway, so take away the $300 and the $400 in Tax rebates and the system actually cost us $1500 - I got $300 off my federal income tax and another $100 from the state My 'break even point' is about 3 to 4 years - It would be higher if I had paid another $1500 to $2K for a professional installation We're remodeling an old farmhouse, so we've never lived here with anything but the solar heat but the tag on the side of one of the water heaters says it costs $400 per year to run - It's a very high efficiency unit with 3 inches of polyfoam insulation, so a lesser water heater would cost more to operate. $500 to $600 per year is probably an average cost for domestic water heating per year for a family of four I REALLY don't understand why there isn't a larger push from the government on solar water heating. Unlike solar electric, or hybrid cars, this technology is pretty well perfected right now and the payback is much shorter than for just about any other 'green' energy source. It can be used in most places in the United States. The outside temp isn't a big factor in how well it works . . . . it depends more on how many sunny days you have If more houses had solar domestic hot water systems, we could make a huge dent in the total energy use of the country and just think of how much less fossil fuel we would consume Don

What you have there is a very desirable feature, and one that I highly encourage my clients to allow me to install. Years ago when they still did laundry in Hot water it was common for water heaters to be set at 180 or 190degF, especially if the water heater was supplying a dishwasher because the health codes require 180degF water for the sanitizing rinse. The Medical profession says infants, children and ppl with sensitive skin can be seriously injured by water temps exceeding 130degF, so the Plumbing codes were ammended limiting the temperature of domestic hot water to not more than 125degF. Now most laundry detergents work fine in cold water and nearly all domestic dishwashers have a built in booster heater to provide the 180DegF sanitizing temp. (When you turn the "power saver" switch on it disconnects the booster heater to save energy). Within a short time it was realized that trained plumbers could be relied upon to set the water heater thermostat to the code prescibed 125degF, but there was no way to prevent the homeowner from coming behind the installer and turning the temperature up, so in order to protect themselves from future liability most domestic water heater manufacteres installed thermostats that only go to about 140degF, and instead of marking the temperture on the control knob they just put an index at 125degF, indicating the correct temp to operate the heater. There is only one small problem with that solution. The human body temperature averages 98.6degF and most ppl like their shower slightly warmer than body temp, which means an average shower is 105 to 115degF and some even like a Hot shower which is in the range of 120 to 125degF. The problem here is that back when the water heater was firing at 180 a typical shower was approximately a 60/40 mix of Hot & cold water, but once the source temp at the water heater was turned down we now have approximately a 95/5 mix of hot & cold water. Keep in mind that even with a code required 2.5gpm shower head a 10minute shower consumers 25gal of water, and if that water is coming from a water heater that is only producing 125degF water, it is very easy to run out of hot water before the shower is completed. Now add to that the fact that most new homes have at least two if not more bathrooms and it is quite common for two or more ppl to be taking a shower at the same time so the supply of hot water is critical. The standard solution today is to install bigger & bigger water heaters, in fact, where a three BR house previously had a 40gal water heater it is not uncommon to see an 80gal heater or even two 60gal heaters in homes today. Now you have to understand that while you are drawing the 125degF water off the top of a typical water heater, that heater is also being constantly filled with 35 to 55degF cold water from the bottom, and as that cold water enters the tank is dilutes the stored water, which results in loosing temperature in your shower quicker. The WATT's tempering valve is actually a mixing valve, so you can turn the temperature up on the water heater and as the super heated water enters the Watts vavle it is mixed with cold water so the output from that valve is at the code max of 125degF. The end result is that you have 25% to 35% more usable hot water from the same size of tank. Now in regard to your original question. I cannot see how it is all hooked up at your house so I cannot comment on the second cold water line, but I have attached an illustration of how we typically install a tempering valve and I am certain you can connect it with just one pipe coming down from the ceiling. The only thing you have to remember is, the horizontal line from the cold water supply to the tempering valve must be connected to the coldwater line before the water heater main water shutoff valve.