I'm in the phase of working with a contractor
to plan my geo system - probably will be a
Domestic Water Well...
and my day has been interrupted to deal with
a failing gas hot water heater.

Should the plan for Geo affect my hot water
heater selection?

Or should it just affect my request for
plumbing to support desuperheater
or other heat source?

The plumbing suppliers I talked to today
don't have a unit that is both gas and indirect.

(This question expires in a couple of hours :-)
Thanks
Seth

Well make certain to plan for 2 tanks...A finishing tank (which would be the 'conventional' water heater you think of) You need to weigh the merits of gas (preferably a direct vent high efficiency unit versus the 60 some percent efficient normal ones (think AO Smith Vertex or similar) versus a heat pump water heater versus a conventional electric. I went with a heat pump water heater and am happy with it so far, you can read more on the topic by searching here. They key is to plan room for both the final tank (of your choice) and a depowered buffer tank (often a 50 gallon simple electric tank not wired, but you can do an 80 or even a 105 gallon marathon tank if you have high heating/cooling demands and a large demand for DHW)

Plan for the buffer tank well described by cschmelz

Main water heater can be tank or tankless. I prefer electric tanks, but if you have NG that may be the better way to go. The trouble with basic tank gas water heaters is that they have a central flue that sucks heat out of the tank 24/7, accounting for their abysmal 60% efficiency.

Tankless is a space saving hi-efficiency solution, but I don't like them owing to their expense, complexity, vulnerability to hard water, and a highly subjective hunch that they might not last as long as tank models. Take that for what it is, just an opinion.

Probably worth plumbing in the buffer now as long as you already have the pipes drained.
Joe

Posted By engineer on 02 Dec 2010 12:43 AM
Plan for the buffer tank well described by cschmelz

Main water heater can be tank or tankless. I prefer electric tanks, but if you have NG that may be the better way to go. The trouble with basic tank gas water heaters is that they have a central flue that sucks heat out of the tank 24/7, accounting for their abysmal 60% efficiency.

Tankless is a space saving hi-efficiency solution, but I don't like them owing to their expense, complexity, vulnerability to hard water, and a highly subjective hunch that they might not last as long as tank models. Take that for what it is, just an opinion.

True, dat, what's worse, with a desuperheater & buffer in front of it, it's firing duty cycle will be even lower, and it will run even LESS efficiently than it's EF numbers.  At steady state most 40-50 gallon gas HW heaters run ~80% thermal efficiency, but that lossy convection loop through the center-flue HX is an efficiency killer at low duty cycle.  At half the EF test usage a 0.60EF heater will run about 42%% efficiency.  If the desuperheater is supporting half or more of your HW heating load, that's where it's going to live, if it's supplying 70%+ of the heat it'll be more like 30%. 

See: http://old.aceee.org/conf/08whforum/presentations/1a_davis.pdf  (look at the low use load profiles for heaters #1 & #2 on p8.)

If going with a tank-type gas unit, at LEAST avoid standing-pilot versions.  If you have the electric service that can handle the load an electric tankless is probably the best option for purely an efficiency point of view or a (not-so-lossy in standby mode than gas and much cheaper than tankless) electric tank.  Gas heaters will drop below 30% efficiency much of the time with a desuperheater in front of it, at which point it's equivalent to running an electric tank off a fossil-fired grid.  If you live where there's a cleaner grid-average 50% fossil fired,  electric finish-heat starts looking a whole lot greener than any center-flue gas unit.

But if 100% of the HW was coming from the water heater  (no desuperheater pre-heat), gas is still a greener option almost everywhere in the US, and electronic ignition + forced draft make a real difference compared to standing pilot/atmospheric drafted units.

Also:  No matter how you're heating the hot water, insulating ALL of the near tank plumbing (cold feed too), with 3/4" wall closed cell foam takes a double-digit chunk out of the standby loss numbers.  (Buy it online, if you can't get it from a local plumbing supplier.  Box stores only carry the 3/8"-walled stuff.)

I started a new thread on a related question

Thanks for all the advice.
Between this forum and a friend
who helped me, I got a standard
50 gallon electric tank.
I had a hard time draining the house,
so we didn't do anything extra at this time.
(Nice taking a hot shower on my handiwork
after the long effort :-)

Next, I'll insulate pipes and add a blanket.

My friend's logic for electric over gas
was different...It's easy to add an electronic
circuit (X-10 or newer technology), so
the tank can be allowed to cool when
no-one is home and rewarm in time
for showers.

This is the same person who has built a
system of thermostats and electronic vent valves
that will give me a 12-zone staem heating system
to use until we can get a well drilled, etc.

Thanks again
Seth