I plan to purchase a tankless water heater to replace a failing water
tank. The current vent is a 6" diameter vent pipe. I need a 7.4 GPM
unit (4 bathroom house with 3 showers) and considering a Rheem
GT199PVN. I noticed some tankless heaters have two separate vent
pipes (one intake and the other exhaust). Some have one vent pipe
with one pipe inside the other. If I choose the later I will need an
additional hole in the side of the house (no chimney). What are the
pros and cons of two separate pipes than just one pipe with an
interior pipe? Are two separate pipes functionally better than one
pipe inside the other? I'm a bit concerned when I need to replace the
new heater (hopefully in 10+ years) that I may have to deal with
patching or resizing holes. I've seen so many different kinds and
configurations in water heaters and vents. Unemployed right now, I
don't have $1600 to spend on installation, I got the time to do it
myself. Any tips on installation are appreciated.
I am definitely a fan of tankless water heaters, but one alternative
to consider is a condensing tank water heater. It will be even more
efficient than a non-condensing tankless water heater. One issue is
that a condensing tank will cost a lot more than a non-condensing
tankless, and while that is often offset by less installation labor
for the condensing tank, since you said you'd be installing it
yourself, that wouldn't apply.
A couple comments. That GT199PVN won't really provide you with 7.4
GPM of hot water--that flow rate is for only a 45 degree Fahrenheit
temperature rise. It's mainly a marketing exaggeration, it would only
apply if your incoming cold water is 60 degrees already and you are
happy with 105 degree hot water. Where are you located? If your
incoming water is actually 50 degrees, and you want 110 degree water
in your shower, then that's a temperature rise of 60 degree, so you'd
get about (45/60) * 7.4 = 5.55 gpm.
Another comment is that 7.4 GPM (if you get a bigger unit that can
handle it) is enough for three simultaneous uses, e.g. 3 showers, or 2
showers and a dishwasher, 2 showers and 2-3 vanities, etc. Depending
on your lifestyle and how many people are in your house, then 2
simultaneous uses might be enough, in which case the GT199PVN is
likely to be adequate (depending on where you live and the incoming
cold water temperature).
Good question, I don't know if separate pipes is a functionally better
arrangement, but it certainly seems like a combined pipe is more
I agree with you that the economics of electric tankless are suspect.
But when I installed a gas tankless, there was no need to increase the
gas service size. Even if there were, I was under the impression the
utility would have done it for me at no cost (unlike with the electric
A non condensing Bosch tankless I have has a EF of 82 or 83, A
Condensing tank I have, a AO Smith Cyclone has an EF of 83 also,
Condensing tank by the true rating of EF is lower than you think, try
to find EF ratings on AO , they are not openly published for just that
reason, most regular gas HD tanks rate 55-60 EF or true overall
Dual pipe would be a cold air intake that saves you a bit. Have you
checked your gas suply with a manometer, and all gas apliances on,
heating system also? Also calculate a % reduction in supply that will
happen on the coldest days, call your gas co. What is your winter
water temp low? I use a 117000 btu bosch and have no complaints with
35-40f incomming , but you need to do your homework before you find it
isnt up to your demands and you are not happy.
I agree...Especially with 4 bathrooms , 3 showers , dishwasher , sinks ,
ect....Would have to be a big tankless unit with a huge gas pipe or large
electrical service , if electric , which would require an upgrade for the
gas or electric service...And your unemployed to boot....Get the old style
tank and hook it up yourself without the major upgrades....Cheap and easy
and not really that much more to run.......
I'm in e.TN. Two adults in the house. The cold water is warm enough
to shower without being heated, although somewhat uncomfortable. An
old-style tank is about $990 (Rheem direct vent), and a tankless about
$1400 (or $1200 if I order online).
Here is nice guide with some venting information.*
Exterior tankless heaters are not required to have outside venting,
If I was building "new" there would tankless installed. A local fire
captain built a 5,000 sf home. He installed 3 tankless heaters,
configured in "zones". One for the laundry, kitchen and garage (inside
garage) Two exterior units at opposite ends of the house. His three
daughter-units have one (3 BR, 3B)
The MBR, Bath and Powder room have one heater on their side of the
Don't hold my feet to the fire, but Bosch TWH indicates the spark
takes place after the hot water is requested from inside the house.
BTW TWHs can last many years and is easily serviced by the home owner.
tankless have high tech electronics and controls, and may need perodic
sediment removal. its best to get a tankless where local experienced
service is available.
from the time water is first drawn, tankless burners turn on and
heated water finally reaches the fixture theres a delay, and waste of
Bob (Goggle Post),
Have you been up close to a tankless system? I understand if not.
You sell yourself as a "hater" of tankless. Not once have you typed
the positive.OR even a negative. Not to point this out but tankless
can be a perfect move/solution.
dont hate them just dont believe they are practical except in very
I post the downsides which unfortunately is a long list...
the vertex is very close efficency wise, without the downsides
I talked with a licensed plumber and he does not recommend tankless
due to the expense and complexity. I called GE and they are giving me
a replacement under warranty. The replacement tank will need an
expansion tank, the reason (according to GE) the first one failed. I
know (liquid) water does not expand much when heated, but apparantly
enough to cause a water tank to fail.
Tankless are generally not recommended by plumbers, but they are
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