I am the guy that has two electric water heaters on the ends of his
house and wanted to replace them with gas water heaters.
I called a gas contractor to look at the set up. He suggested a Rannai
Tankless Gas Water Heater. He said it mounts on the outside wall - on
our house it would be perfect right by the gas meter on the wall just
outside the bathrooms. We would have instant hot water on demand. We
would run a copper tube up and through the crawl space to the kitchen
for the kitchen sink and dishwasher. We would insulate that line for
This whole thing would eliminate lots of problems. It would eliminated
two 50 gallon tanks sitting there heated for two adults. It would cut
out the long 3/4 copper that runs 80 feet through the concrete. We would
get two - $450 rebates form the city for getting rid of two electric
We would also run a natural gas drop for gas fireplace logs and a dryer.
Wife will be happy with fireplace logs - a gas dryer. I will be happy
with endless instant hot water in my two showers.
See the water heater at -
He has several installed in town - we are going to go look at them - and
talk to customers.
Please criticize this plan - am I missing anything? What pitfalls will I
I value advice on here - anyone running a Rennai?
Rinnai have electric heat provision to keep the units from freezing to
5f, but what about When your power goes off or When the electric freeze
protection fails, you then loose that nice unit. Unless you live where
it never gets below freezing . How cold does it get where you live.
Inside mounting is always safer plus the controls wont be subjected to
weather. Rinnai otherwise looks very good and efficient.
I guess the model I looked at had different freeze protection.
But who needs the risk of putting a 1000$ water heater outside that
could be ruined in minutes with the power going out
Also consider the wasted money heating an outdoor water heater,
there goes alot of the savings you just paid $$$ to get.
I say put it inside if your area freezes.
I am in Florida where we do not freeze. I want the unit outside to avoid
venting it. Florida is a different world. We do not winterize our
campers :-) People store lots of things outside in the yard. We
sometimes store our cars there up on blocks :-)
Also in Florida - we AC a lot. It is warmer outside than inside most of
the time - so you save money by having it outside :-)
I am currently heating two 50 gallons water heaters with electric at
$600 a year each - total $1200. This unit will cost about $150 a year to
run. There figures come from the local utility company - not the Rennai
company. The utility company here sells both electric and gas. They will
give me $900 to get rid of the two electric water heaters and go to gas.
I live in Tallahassee - it seldom gets below 30 here at night. But the
unit is supposed to be protected down to -30. Since the unit is attached
to the outside - there is no venting or gas inside.
I personally would convert to one of these if it were only the cost of the
heater and installation. In my case the 1/2" gas piping would need to be
replaced with 3/4" at a significant extra cost.
Sounds like a win-win for you though. With the rebates and upgraded
fireplace and drier you get plenty of bang for your effort and the plumber
gets a significant job with lots of labor and moderate materials cost (very profitable for him).
If it were a small home with only one water heater, you might stick with the
tank because it is less expensive up front (even with conversion to gas) but
the second tank being gone will free up valuable space not to mention the
electricity savings. It is likly that the tankless unit cost less than 2
new tanked units. Tank units only last 5-10 years anyway. You will really
reap the benifit when you don't have to replace the tank later.
Might as well pipe in gas for the kitchen range too. Even if you use
electric now and don't plan to replace it for a while, it will add value to
the home and give you more options in the future.
You may have "instant hot water on command," but it isn't necessarily going
to be at a constant (or safe) temperature. Try to find some place to try
them out, especially for a shower.
In my experience, tankless heaters were a difficult-to-control cost-cutting
second-best alternative for use in places where a hot water tank wasn't
possible -- e.g., low-cost housing or very small apartments. I've used
several tankless heaters while living overseas and wouldn't want one here.
The one's I've used didn't give you the constant temperature /constant
volume flow you want when showering. The problem comes if there is a sudden
change in water pressure such as when someone turns on the cold water or
flushes a toilet. Not only do you have less cold water for a few moments,
but the hot water flow decreases, which increases the hot water temperature,
so you simultaneously lose the cold water and increase the temperature of
the hot. Also, as you try to adjust the temperature, if you decrease the
hot water mix too far, the heater will sense you've stopped using hot water
and turn off, giving you a sudden shock of full cold water.
The problem existed with both gas and electric-powered tankless heaters --
the heaters were used because the small apartments didn't have room for a
It's possible that computerized controls have solved some of these problems,
but I'd proceed cautiously, and not expect the same quality of showers as
with a tanked system, and be especially cautious if you have young children
who may take showers.
Any of the decent tankless units (Rinnai, Takagi, etc.) will regulate flow to
keep the output temperature constant.
What happens with a conventional water heater when some bozo flushes the toilet?
Assuming you don't have a pressure-compensating valve, you get scalded. No
different with a tankless unit. You'll also get the opposite effect with a
tankless if someone really draws a lot of hot water (and I mean a *lot*, not
just a couple of simultaneous showers) -- the hot pressure will drop, and you'll
freeze. Certainly not a reason to avoid a tankless unit. I've been more than
happy with my Takagi TK-1. Of course, when I redid my plumbing a few years
back, I installed pressure-compensating valves in all the showers -- probably
the best money I ever spent on plumbing fixtures.
Built a custom home last year and decided to put in a tankless
waterheater over the 2 50 gal water heaters the architect
thought would be right. One reason - reduce the amount
of heat need to maintain water temp in tanks.
We love it. We have 2 adults in the house - no kids, etc. And
it works for us. I'm happy to know that while we're away
or during the day, there's no hot water being maintained.
The ONLY downside is that hot water is on demand and that
means that you have to run thru a bunch of water to get
it hot. Normally not a problem. But we live in an area that
has seen drought conditions (tho not for the last couple
of years) so I only would be concerned about it then.
I'd say go for it. I think we have a Rennai
I thought that the non-tank hot water heaters were supposed to be
"instant on" or and avoid the problem of running through a bunch of
water to get it hot.
Could this be because your running the hot water supply through a long
path of pipes?
For gas on-demand water heaters, I believe that there is a 7-10 second
delay while the burners fire up and the exhaust fan (on models that
use one) comes up to speed. Some models have a standby feature for 60
seconds after the hot water is turned off, where if it is then turned
on again, the delay is only 1-2 seconds.
These delays are, of course, all on top of the need to empty any
cooled water between the water heater and the fixture.
My small Bosch fires up in 3-4 seconds , I dont realy notice any more
time in pushing out the cold water in the line. The only drawback is if
you only want maybe less than the 1 or 1/2 gpm it takes to turn the unit
on, then it is cold.
But Ng savings have made me adjust to its use and realise that at
117000 Btu it takes alot of energy to heat water, because of this I`ve
become more energy consious using hot water much less. My furnace on
low fire is 47000 btu and heats my 1200sq ft house easily at -20f, it
makes you realise that 117000 btu to heat water is just money down the
drain. Tankless and small tanks have been the norm in energy poor
countries for 50+ years, its about time we wake up to their savings. Now
with their modern controls they realy are comfortable to use. Although
expensive I calculated a 4-5 yr payback over electric tank, a good
Keep in mind that the 117000 BTU is for one hour of continuous use. Who
runs hot water fro one hour straight? Even a furnace that burns 47000
BTU - seldom runs for a full hour straight. I used to have a furnace
with an hour meter on it. On the coldest winter day - it only ran 6
hours a day. In the summer - to make hot water - it ran about 30 minutes
Depending where you live, it would probably be better to find a place
inside to put the heater. Rinnai has an optional feature that dumps the
water from the unit at a certain temperature. They also have multiple
point of use t-stats to allow cooler water at the shower/tub and hotter
water in the kitchen.
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