On Fri, 25 May 2018 15:04:14 -0700 (PDT), trader_4
wrote:

On Friday, May 25, 2018 at 2:38:36 PM UTC-4, wrote:
On Fri, 25 May 2018 11:08:39 -0700 (PDT), trader_4
wrote:

On Friday, May 25, 2018 at 1:44:06 PM UTC-4, Mistert wrote:
replying to PipeDown, Mistert wrote:
I have a small 1800 sq foot home 2 full bath and 2 old fogies live here
retired and i want to go to the tankless Eco 36 but have 200 not 300 amp svce.
and we never have 2 showers at once just a load of clothes. Do I have to add
more elect'l service?

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It's 36KW, so it needs 150A. With 200A, you only have 50A left for everything
else. So, what are the other significant loads? AC? Electric ovens?
Cooktop? Dryer? Add it up and you'll have your answer. Even one of
those other loads and you're close to the limit. I think for
most people, tankless makes no sense, for a variety of reasons. Starting
with that I don't believe the operating cost savings justify the larger
upfront costs. The essential difference is you're eliminating the standby
losses of a tank type. Electric tank you can buy one of those extra
insulation blankets and pretty much totally enclose it in more insulation
which will reduce the losses.

He might want to think about downsizing the heater to 24KW,
understanding that that might limit the hot water he can use at any
one time. The things that will end up competing will be an electric
range and the dryer but if you have 100a to work with that might not
be problem 99% of the time. Only having 50 could be problematic.
Without a load calc it is really hard to say what he can do.
I tend to agree with you, tankless water heaters may have a very long
payback time if you don't have natural gas.


The payback is even worse if you have natural gas. They suck up gas
like they suck up electricity, so you typically have to run a bigger
gas pipe from some big tap off, maybe even all the way from the
meter. And gas heats cheaper, so that makes the pay back take longer.
Here, the summer gas bill is under $20, which includes hot water and
some gas grilling. What you're saving is mostly the standby cost,
of the $20, that can't be all that much. Even if it's half, $10 x
12 months = $120. And I just have a basic water heater, for a couple
hundred more you can get higher efficiency too. Running gas, the cost
of the unit, it's a lot to pay back.

It is worse than that. If the furnace is on, there is no lost heat at
all. It still goes to warming the house. It is like all of the other
energy you use in winter. The only real wasted energy is what escapes
the envelope of the house and the hot water you send down the drain.