Since there's been some discussion about these critters here lately, I
thought I'd add my take on them. I have three customers who actually
have them, so I speak from some experience.
First of all, the answer to questions like "should I install one?", "are
they more efficient/cheaper/better than a tank heater?" is definitely
"it depends". It depends on (in no particular order):
o where the heater is installed (how far it is from the farthest faucet)
o how big the heater is
o the water usage pattern
The last probably being the most important.
Two of my customers have the same type of older-generation tankless
heaters (Aquastar, a French-made unit, now handled by Bosch for spares).
Two of them are installed in the attic crawlspaces of a
commercial/residential building, probably because the remodeling
contractor didn't want to sacrifice any more space in the living units
than necessary (and also simplified venting, since they're right under
the roof). This makes these two a pain in the ass to service; I've
overhauled both of them (replacing water valves and thermostats). Still,
they operate pretty well.
One of these had an odd setup, which it took me a while to figure out.
Someone had written "OPEN 3/4 TURN" on the inlet valve, and it turned
out that sure enough, the heater would simply not function correctly if
it was opened any further. Not enough hot water in the shower, though
the kitchen sink was OK. The culprit was the shower valve, which was a
strange one that was full-on with temperature control; there was simply
no way to have anything less than full flow in the shower. This shows
that there's a definite limitation to how much flow these heaters will
Another customer has this same heater in their fairly large house.
They're very happy with it; they have plenty of hot water and their gas
bills are lower.
My other customer just installed a Tagaki heater outside her house. This
unit is remarkably small, requires no venting, and supposedly has a much
higher capacity (and is more efficient). (Having electronic ignition
doesn't hurt, either.) I'm told that this is pretty much the state of
the art today. Too early to tell how it'll affect her gas bill.
One thing that ought to be considered is insulating hot water pipes to
further avoid heat loss.
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conversation with the average voter.
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