Re: Replace a water heater: what to get.

 On Thu, 16 Sep 2010 02:20:43 +0000 (UTC), Gordon


The decision should be made based on local environmental, cost and
usage factors.

Were are you located?  (Climate)  
Average Heating degree days? Cooling degree days?

What is the year round average air temp?
  Note: Average air temp usually == Incoming water temp.

Preference for water temp?
What is your hot water usage profile?
Are you consider changing that profile?
   Replace top loading washer with more efficient front loader?

Available solar flux at your location?  (flat panel tilted @ lat or
@roof angle).
  Do you have a substantial roof area facing towards the morning sun?
  Location of any Shade trees? Any plans to plant more Shade trees?
  Is your roofing material nearing it's EOL and  ready for
replacement?
  Do you have an unfinished area to accommodate a couple of hundred
gallons of water tanks?

Price of grid electricity?  What are the price/usage thresholds??
Price of Natural Gas?

Generally Natural Gas is cheaper to operate,
  but more expensive to install and maintain.   Same goes for solar,
even more so.   Cheap to operate.. more expensive to install and
maintain.

  I have used a tankless for heating my house and hot water for a few years
now. If you have any hardness in your water you may live to regret it. You
will have to flush the unit with 3-4 gallons of vinegar two or three times
per year to keep it working half decently. This requires a small circulating
pump and a large bucket and some hoses with the right ends etc...

Think of your kettle scaling but five to ten times worse. It just stops
working instead of getting slower. Many valves and switches in the water
stream to gum up and the vinegar rinse pumps do not get to those parts while
it is unplugged. Special flushing bypass valves are a necesity to own one of
these high maintenance jobs. In a tank unit the lime is at the bottom of the
tank and does not affect the process as much. Electrci tanks have been shown
to be the cause of Legionella bacteris under the bottom element where the
water doesn't get hot enough to kill the build up. Gas has never been shown
to do this in researched samples done in Quebec.

Tankless have not really proven any more efficient than a tank unit. The
factory tests show they are but in real usage they have not proven any
better.

I used to have a small 30 US gal (22.5 Imp gal.) tank water heater. If you
ran out of hot water in the shower a simple shut off and lather your hair
for two minutes and hot water was available again. The larger units take
much longer to heat up with the same BTU burners in them.

Cold water sandwich is the term people use to exemplify the cold water surge
you can get from intermittent hot water usage. You have the pipes heated up
and then turn on the hot water tap. The unit takes about 1/2 sec to fire up
again and there is a long shot of cold water in the pipe that will shock you
slightly in the shower.

Another problem is the low flow sensing. With the low flow water saving taps
used these days if you only want a low stream of luke warm water (maybe
washing your face) the tankless may not see enough flow and it shuts down
giving you cold water.



OP here:
Thanks for the info. Tankless would have another advantage around here;
No tank to fall over in an earthquake.  If they aren't much more
expensive than a tank model, and they can run durring a power
failure, then I see no reason to not have one.