We need to replace our water heater, and are considering a Rinnai
Tankless water heater. The household is two adults living in
Minnesota. So, the temperature rise would typically need to be 70
degrees. The biggest draw in the house is a soaking tub. This would
be the only thing drawing hot water when in use.
I see that Rinnai has two models, 2532FFU and 2520FFU. Looking at
their charts, both units perform the same after you have to heat water
60-65 degrees or more. Are there any real world advantages to the
2532FFU? Does anyone have experience with these units that lives in my
neck of the woods? What kind of maintenance is needed on these
I notice that Rinnai recommends a 3/4 NG supply. The plumber that came
out to take a look at our setup, said that my existing lines will work
fine. There is currently a 'main' line in our utility room. He said
they have installed units in the area without having to change the NG
lines. What are the possible ramifications of using the smaller NG
Anything else I should know before making a decision?
Thanks for any feedback,
You don't guess at the supply size. It's determined from the
appliance capacity and pipe size/length.
The appliance needs a minimum pressure at the regulator
inlet (usually 7 in H2O) when its own useage plus all
other appliances is taken into account.
What is the difference of the 2 models. Here is my experiance with a
Bosch 117000 btu unit and my take on what you need to know. You can`t
guess at Ng supply it needs to be measured with a manometer with
competing apliances on, if you dont get the flow you wont get 100%
output when you need it when in winter water is at its coldest. This
means knowing main input also. A Ng 3/4" line, im guessing you are
thinking 190000 btu Rinnai, My 117000 btu Bosch needs 3/4 at 10 ft or
more run, as I mentioned competion affects flow, I measure 2f drop in
water temp with my furnace competing.
Inlet water temp in winter for me can be 33f at -15f, you need to
knows your lows and take off 5f for saftey in sizing, but you probably
don`t know your low incomming temp as now is mid March.
Now measure output temp at your HWH and at a furthest shower, mine
drops 6-10f with insulated pipe in 30ft. I have no problem with a 112
shower temp with 33f incomming with unit not even on high so the big
Rinnai can handle most everything unless your gpm is to high or Ng flow
to low, I only have 4gpm. For a tub it will be fine, it will fill a
swimming pool. What is your Gpm incomming, tankless are rated at a temp
rise of a gpm. So sizing everything is critical.
Get a unit that keeps output temp even, my bosch monitors rise, not
output temp. A remote thermostat is nice to, the better Takagi and
Rinnai keep an even output temp. Takagi makes Bosches better unit.
Ive only heard you have no Rinnai Warranty unless a Rinnai certified
installer does the job, and a "plumber" that just says, without
checking, that your Ng supply is great is a, well, maybe, might be, a
hack. Poor testing, poor planning, you might be unhappy.
I've done quite a bit of looking into for the Tankless solution.
Stay away from Bosh, especially the low end units
Only go rinnai if you have a Licensed person install it as if you do it, the
warranty is void.
The Takagi is what we chose. the T-K2. Its for a 840sqft Granny unit. 1.5
Bath, Kitchen and garage Sinks and Dish Washer. LP though.
Let me know if you want more info.
depending on your water pressure, some places like ours need cold and
hot turned on for sufficient flow at the upstairs showerhead. at our
home we only have 42 psi from the city water coming thru a new one inch
you may want that hot water at 140 degrees for you and the dishwasher.
this means a rise from cold city water 105 degrees at whatever gallons
per minute you have. whether any tankless unit can achieve that depends
on the entire home system for gas, water pressure psi, water flow gpm,
personal preferences, and future owner needs. i can't imagine we'd
enjoy waiting for the tub to fill with barely hot water more slowly
without the cold flow that speeds up the process. we use a regular gas
75 gallon water heater.
Even in the most Northern of the States, inlet water temperature below
50 degrees Fahrenheit is very unusual (I'm in MI, btw). Expected
faucet temperature is generally in the 120 degree range (hotter can
scald), giving a max expected rise of 70 degrees. I've never heard of
anywhere where the inlet water is essentially ice at 35 degrees. I
suppose if you were taking water out of a shallow pond this could be
the case, but water pumped from underground will never get this cold.
For Lefty, I'd suggest you are on the right track with your questions,
and the only advice I would give you is to do a complete assessment of
your simultaneous volumetric needs. For example, while you mention a
soaking tub (which either of the heaters you mention will handle just
fine on its own!), you should assess whether a simultaneous dishwasher,
clothes washer and shower situation might ever occur. Maximum draw is
not based on a single application. If you are convinced that your
maximum need will be 5gpm or less then the Rinnai will suit you fine.
If you need more, then you can hook up 2 or more in parallel (NOT
series) giving higher heating capacity (we're starting w/ 1 and
planning to add a 2nd as our children get older).
As for the 2532 vs. the 2520, I'd ask the rep some questions - the
volume flow rates in their online brochures simply don't make sense
(for example, GPH should be GPM * 60, but isn't; 2 tanks should be 2x
volume flow from 1 tank but isn't.
I guess you have never heard of house incomming supplys freezing needing
a big welder to thaw them out at -20f. Well im south of you and many
"summer" homes here on the lake or anywhere can have substandard
hookups. My case is my hill is eroding where my main is embedded and Ive
measured 33f with an acurate thermometer on a -18f morning. 50f is only
way way below frost line, sure the City pumps 50f water but unless you
test it yourself on your coldest day you might be out of showering next
winter on a major freeze spell. Now thats kinda dumb to not figure in a
15f more drop, isnt it.
A big 190000 btu Rinnai or Takagi will handle a house, my 117000btu
little Bosch gives me a hot shower at 34f incomming without it being
even set to its highest.
Yup, good point - designed poorly enough any water inlet can freeze.
Given, however, that the original poster indicates he believes only a
70 degree rise will be necessary, I think we can safely assume that his
house was built correctly and the city water pipe is below the frost
line. Otherwise the city would be out there with a giant blowtorch as
The rinnai unit works very well. I've installed many of them. Basically,
they are maintenance free. The main consideration is line sizing for
the gas lines. They fire at about 3 times the rate of a tank type unit.
Hence the need for proper line sizing.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.