> But I just did a little calculation for my house. To support 140F water
> (Yes, I like my hot water hot) and potential simultaneous use of 2
> showers/tubs; a dishwasher; a clothes washer and a single faucet, I would
> need somewhere around 130 kW ! At 240v, that's over 500 amps !
That's a *huge* amount of simultaneous water usage.
> And all this to save perhaps 10-20% of my natural gas bill. I pay roughly
> $100/mo for nat gas, so the projected savings is $20/month. $2200/20 = 9
> years just to break even, ignoring interest I would have earned if I'd kept
> the money in the bank.
Agreed, tankless doesn't necessarily make sense on a straight economic
basis. We went tankless because I wanted the space where the water
heater was. Tankless let us put the water heater in the attic, out of
the way.
As for the professional installation, they're mostly not difficult for a
DIY installer, I bolted ours up and it worked fine.
In our case the biggest single 'Whoops!' comes if you've got two showers
going and someone starts the clothes washer. The washer pretty much
sucks all the hot water out of the house. Of course, since there's only
two of us, that doesn't happen often...
The apples vs oranges assessment:
With a tankless water heater you have only X total hot-water flow
available. With a tank-type heater you can run hot water out of every
valve in the house, until it's all gone.
Problem is, once it's gone, it's gone, and you're waiting a good long
time to get *any*. With tankless, you can run hot water all day long as
long as you don't run too much of it at any one time.
Tank-type water heaters heat the water to a set temperature. No matter
how cold the incoming water, the output will (should) always be the
same. Tankless water heaters have a maximum output temperature setting
but as flow increases, if the incoming water is cold it may not be able
to reach that maximum.
This is I think something many folks overlook, you may get 9 or 10gpm at
140deg out of a big tankless if the input temperature is 70 degrees, but
if it's 35 you may only get 5.5gpm before the output starts to cool off.
Our Noritz N-084 is rated at something like 220000BTU, which needs a
3/4in gas line all to itself; between that and things like my wife's wok
burner we ended up with a 1.25in gas line post-remodeling.
John.
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