I just had a person that rates houses for energy efficiency come and
rate our house. One of his suggestions he made was to pull out my existing
Gas fired hot water tank and install a Tankless hot water heating system.
We don't have a family living here only my wife and I and we're both away
through the day working .....so the hot water demand is only morning and
evenings. It makes sense when he explains it. He says "why have a large tank
down there heating water 24/7 when your demand is about an hour a day?"
Are there any disadvantages to this tankless system? Does anybody here
have one that would care to comment? Thanks.. Jim
Some people love them, some hate them. Nothing is perfect and nothing is
worthless. However, before condeming tank water heaters, your "consultant"
should have explained the difference between an old style low efficiency
tank heater that you probably have, and a high efficiency tank heater and
those inbetween. High efficiency water heaters just sip the gas and can
supply continuous hot water similar to a tankless yet still have the reserve
of a tank of hot water available.
Your existing tank isn't heating the water 24/7. It heats it to the set
point, then turns off. The tank is pretty well insulated and will hold the
heat fairly well. The heater only kick on for short periods to maintain the
set point. The tankless method requires lots of energy for the period when
hot water is being used, then sits idle. There is probably some savings, but
I doubt it's huge
About the only way to really make this hit home is the hard way. Go to
your water heater and sit there for 24 hrs. Watch how much it DOESNT
run! Then call the guy back up that came to give you this so called
house efficiency rating and call him the uninformed hack he is.
Nothing wrong with tankless but if you are purchasing one to save
money by increasing efficiency you have to understand the whole
Actually because you have such low usage, it will take you all that
much longer to recoup the cost. I would think high usage would make a
better argument for spending the money on a tankless system by
replacing a perfectly good tank prematurely. At least I'd wait until
you HAVE to replace the current tank (at 11 year point depending on
your water corrosiveness). Then at least you can subtract a new tank
cost from the new tankless cost and start your recouping from there.
My water heater died about a month ago and I took a quick look at tankless
before I bought a new gas tank style.
If you and the wife only take showers and your winter ground temp is warm
then you might break-even on the extra cost in 10 years.
If your winter ground temps are low you should really study the temp rise
factor. How much a tankless system can raise the incoming water temp.
They work for some people and they don't for others. I prefer clean dishes
from the dishwasher and a Jacuzzi full of hot water for my aching back in
the cooler months.
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Main disadvantage to me is the high cost to install them and replace them
when they go bad. especially if it is an old house with the tank already
If you are in an area that looses power, the small 5 KW class generator will
heat the water in a tank.
A well insulated tank has minimal loss over the course of a day. Do you hear
it turn on often when water is not used? Probably not. Some tanks will only
drop 6 to 10 degrees in a day, using little energy to maintain a reservoir
of heated water. In the case of heating season, there is no loss if you are
heating that portion of the house anyway. So, your have to figure payback
on only six months a year.
Price out one of the tankless models and the cost of installation. Then you
will think that what he says makes little, if any, sense. Then go enjoy a
nice beverage knowing that you are really rather efficient and cost
effective with what you have.
The thing about a typical gas water heater is that it has a chimney
going up the middle of the tank, which is obviously not insulated
because it is part of the heat transfer path when the burner is
running. So you get significantly more standby losses from a gas
water heater tank than from an electric water heater tank.
For example, with an 80% efficient burner, a gas water heater will
have an Energy Factor (which includes the standby losses) of
0.60-0.65. So the standby losses are 15%-20%. By comparison an
electric tank water heater can have an energy factor of over 0.95, so
the standby losses are less than 5%.
I'd say one big disadvantage would be that you may never come out
ahead financially. I have a typical gas water heater, not high
efficiency, and in the summer, when it's the only gas load, my bill is
less than $20. And that includes actual water usage as well as the
standby losses, which obviously aren't very substantial..
You may also find that to get the right size tankless requires a
larger gas service, increasing gas pipe size from the meter to where
the tnakless is located, etc.
If you can, do a simple experiment sometime. When you're going to be
away for a few days to a week, record the gas meter reading, make sure
the water heater is the only usage, ie turn off any other pilot
lights, heat, etc., then read it again when you return. That will
tell you how much you are paying for standby losses.
And as others have pointed out, these losses can be cut down
substantially by going to a high eff gas tank water heater, which is
still typically a lot less than the install of a tankless. These
close off the exhaust vent when the burner is not running, which
substantially cuts the heat loss. I'd be looking at those when it's
time for a new water heater. However, one other thing to consider is
there is currently an energy tax credit in effect and some of these
solutions could get you a credit for up to 30% of the cost. If you
have a tank that is nearing the end of it's life, now may be the time
to replace it with something.
There are tankless designed to do 180 all day long, but what a waste
it is to heat a tank to 140 just for dishes. My dishwasher has a
preheater and I would never buy one without. An AO Vertex or Cyclone
is also expensive, saving energy is an investment and it costs money.
Yes, I don't see why you can't get 140F water out of a tankless.
They are spec'd for a given temp rise. All you need to do is figure
out your incoming lowest water temp and what flow rate you want to
support to size the unit. I have my tank set at about 130 and the
dishwasher works fine.
Yes, they have a certain temp rise capability. And it ain't a hundred
degrees. The incoming water in our area in the winter is about 38
degrees. Heat that with a tankless and it'll dribble like an old man
with an enlarged prostate.
Oh really, I heat 35-36 incomming to a hot shower without even my
little 117000 Btu Bosch on high. I used 3/4" gas line for a 6 ft run
and did a Manometer test in winter, because I know in winter pressure
drops with high demand at -15f -20f. And I will bet anything, of the
the units you complain about you never tested gas flow with a
Manometer when water was 38f with all the homes competing gas
apliances on. Its a fact in my area even mains flow pressure is
reduced on the coldest days up to 20 %. As far as temp, there are
Tankless designed to run radiators to 180f. You complain about
tankless, but I bet you never tested gas flow in winter. There are im
sure many jobs where they cant be put in and get 100% output because
of meter or main issues.
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