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1. 
   Michael Chandler | Apr 05, 2009 01:42pm | #1

   The answer hear depends on a number of factors. Are you getting electricity from coal? do you have access to natural gas or are you looking at LP? how is your house laid out?

   My preference in general is to avoid heating water with electricity and provide a pipe design that cuts down on waiting for hot water.

   This leads me to locate a tankless gas water heater near the kitchen and to pipe hot water from it to a small electric tempering tank near the master bath so as to minimize the wait for hot there. Even a 5 or 10 gallon under counter tank will work.

   We had an electrician run 220 to one of these recently and fry the element. The heat from the demand water and daily usage kept the tank warm until the owner went on vacation and discovered the mistake. This configuration uses very little electricity.

   Gary Klein has done a lot of research on hot water distribution and structured plumbing systems to optimize efficiency and one of the interesting results was the discovery of the mixing effect of elbows in the line. If you've ever waited at the sink for hot water and felt it slowly go from cold to lukewarm to hot-ish to... finally... hot then you know that the hot water doesn't simply push the cold out of the pipe ahead of it but mixes with the cold and gradually warms up the standing water in the line. Simply eliminating all elbows and tees that function as elbows does a lot to improve delivery. The most critical elbows to avoid are the ones closest to the water heater.

   Tankless water heater options have really seen some changes recently. Rinnai is under attack by other manufacturers wanting to take away it's market dominance. Rheem (Pronto) and Tagaki came on strong for a while but Navien is making up for lost time with condensing demand water heaters that hit up near 95% efficiency with some models having a recirculating hot water system built in and a tempering tank to eliminate the hot water sandwich effect. These features come at a cost of 15 PSI pressure drop at 5 gpm which is a deal killer for me.

   I've been a certified Rinnai dealer for years (I'm a licensed plumber and just got an electricians license for solar purposes) but the condensing demand water heater we are installing these days is manufactured by Quietside. Its not as powerful or deeply modulating as the Rinnai but it vents through the roof with 3" PVC and has very low pressure drop which makes it useful for use as a side-arm boiler to a tempering tank for closed loop radiant floor applications with solar pre-heat.

   I build in North Carolina where our cooling loads far exceed our heating loads and we have problems with late summer BTU dumping in ground source heat pumps so I don't use those systems on my homes and can't really give advise on water heating GSHP systems.

   Hope this helps, nothing is ever "the perfectly right answer" but given the right information you should be able to get pretty close.

   Michael