Home Repair forum - More on tankless water heaters

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More on tankless water heaters

David Nebenzahl

2008-04-03, 3:25 am

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 XXX 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
handle.

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.

--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill

BobK207

2008-04-03, 3:25 am

On Apr 3, 12:11=A0am, David Nebenzahl <nob...@but.us.chickens> wrote:
> 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 XXX 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
> handle.
>
> 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.
>
> --
> The best argument against democracy is a five-minute
> conversation with the average voter.
>
> - Attributed to Winston Churchill

If you're listing issues.......

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

better consider as well

o temperature of incoming water
o elevation (above sea level) of installation

if the incoming water is really cold (like sub 45) and / or
installation is in the higher elevations (like the mountains) forget
about a tankless

cheers
Bob

hallerb@aol.com

2008-04-03, 9:25 am

> if the incoming water is really cold (like sub 45) and / or
> installation is in the higher elevations =EF=BF=BD(like the mountains) for=
get
> about a tankless
>
> cheers
> Bob-

some tankless manufacturers alsao mention installing 2 in series,
thats good they sell 2 per install.

careful attention to large enough flue and gas line sizes are
necessary.

David Nebenzahl

2008-04-03, 1:26 pm

On 4/2/2008 11:21 PM BobK207 spake thus:

> better consider as well
>
> o temperature of incoming water
> o elevation (above sea level) of installation
>
> if the incoming water is really cold (like sub 45) and / or
> installation is in the higher elevations (like the mountains) forget
> about a tankless

That's interesting; hadn't thought of that. So what do you think is the
maximum practical elevation for a tankless to work properly?

--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill

glen stark

2008-04-03, 5:25 pm

On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:

> better consider as well
>
> o temperature of incoming water
> o elevation (above sea level) of installation
>
> if the incoming water is really cold (like sub 45) and / or installation
> is in the higher elevations (like the mountains) forget about a
> tankless

Why does the elevation make a difference?

Oren

2008-04-03, 5:25 pm

On 3 Apr 2008 21:20:25 +0200, glen stark <mail@nospam.glenstark.net>
wrote:

>On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>
>
>
>Why does the elevation make a difference?

It's not a factor, as best I can tell.

Wayne Whitney

2008-04-03, 5:25 pm

On 2008-04-03, glen stark <mail@nospam.glenstark.net> wrote:

> On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>

Bob, rather than forget about the tankless, just bear in mind the need
to upsize the unit appropriately, of course that may make it less cost
effective.
[color=darkred]
> Why does the elevation make a difference?

Good question--it definitely makes a difference, boiler manufacturers
will have a high altitude kit to change the burner orifices to
compensate for the altitude. As to why, my WAG is that since the
natural gas is delivered at a particular PSI gauge (relative to
atmospheric), the absolute pressure delivered is lower, and so the
flow rate in moles/hour is lower. Plus the oxygen pressure is lower,
so the burners may need to be reconfigured to provide comparitively
more air.

Cheers, Wayne

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