I'm considering replacing a 40 gal water heater with an Rinnai tankless
heater. The Rinnai has a flow rate of 8 gpm. The shower in the master
bath has a 2.5 gpm rate but there are six 2.5 gpm body shower spray
heads mounted in the walls. Will the Rinnai have enough capacity to
provide hot water if all heads are in use?

Since this is a new house I'm not sure how well the heads worked with a
40 gal tank.

Any advice/info?

In article . com,
"bobby" wrote:

I'm considering replacing a 40 gal water heater with an Rinnai tankless
heater. The Rinnai has a flow rate of 8 gpm. The shower in the master
bath has a 2.5 gpm rate but there are six 2.5 gpm body shower spray
heads mounted in the walls. Will the Rinnai have enough capacity to
provide hot water if all heads are in use?

Since this is a new house I'm not sure how well the heads worked with a
40 gal tank.

Any advice/info?


6 x 2.5 = 15, unless showers use a different form of math OR 2.5gpm is
the MAX flow you are SOL

In article . com,
says...
I'm considering replacing a 40 gal water heater with an Rinnai tankless
heater. The Rinnai has a flow rate of 8 gpm. The shower in the master
bath has a 2.5 gpm rate but there are six 2.5 gpm body shower spray
heads mounted in the walls. Will the Rinnai have enough capacity to
provide hot water if all heads are in use?

Possibly, depending on your cold water temperature and how hot you like
your showers.

Remember, 8gpm is the maximum hot water flow, but most people don't turn
the shower up to 120 F. Let's say for simplicity that you like your
shower with the knob straight up, equal proportions of hot and cold
water. Then you'd need (7x2.5)= 17.50 gpm total water flow, and half of
that, or 8.75gpm, would need to be hot water. So 8gpm isn't quite
enough. But if you restrict the flow on each head from 2.5 to 2.2, your
total would be 15.4, 7.7gpm hot.

But let's double-check those numbers. At 17.50 gpm total, if half is
hot, your 40-gallon heater should now run cold after less than five
minutes. Does your shower really suck that much hot water?

--
is Joshua Putnam
http://www.phred.org/~josh/
Braze your own bicycle frames. See
http://www.phred.org/~josh/build/build.html

We're buying this house this week so I don't know how long the
previous owner was able to run the showers. Sounds like something I
should ask him the next time I see him.

"bobby" wrote:
I'm considering replacing a 40 gal water heater with an Rinnai tankless
heater. The Rinnai has a flow rate of 8 gpm. The shower in the master
bath has a 2.5 gpm rate but there are six 2.5 gpm body shower spray
heads mounted in the walls. Will the Rinnai have enough capacity to
provide hot water if all heads are in use?

Since this is a new house I'm not sure how well the heads worked with a
40 gal tank.

Real unlikely. Assuming 50F cold water, 120F hot water, you're going to need
8.75gpm of hot just to get 85F water. Most folks prefer a shower closer to
body temperature (say 100F), so you're going to need even more gpm out of the
heater. And that assumes that you truly are getting 8gpm out of the water
heater. Check the output curves -- you'll often see a marked reduction in
output if the input water is particularly cold.

On 8 Dec 2004 18:28:42 -0800, someone wrote:


Since this is a new house I'm not sure how well the heads worked with a
40 gal tank.

They might work well, but certainly not for long - unless someone
liked cold body sprays.




Reply to NG only - this e.mail address goes to a kill file.

On Wed, 8 Dec 2004 21:51:46 -0800, someone wrote:

Remember, 8gpm is the maximum hot water flow, but most people don't turn
the shower up to 120 F. Let's say for simplicity that you like your
shower with the knob straight up, equal proportions of hot and cold
water.....

It is unwaranted to equate the "knob straight up" with being equal
volumes of hot and cold water. It seems unlikely that the average
person would want such a lkewarm shower anyway. If the tank is at 120
degrees, and the incoming cold water is 60 degrees, equal volumes
would only yield a 90 degree shower. Even 100 degrees is not usually
percieved as a "hot" shower, and that would take 80 degree incoming
cold water. Not many domestic hot water tanks are over 120 nor should
they be for safety reasons.

Neither the existing nor the proposed alternatives appear to be
sufficient, but at least the existing tank can give 2 minutes of use.
What is the impetus to convert to tankless anyway?

-v.


Reply to NG only - this e.mail address goes to a kill file.

What is the impetus to convert to tankless anyway?

Primary reason is to save space. This house has two 40 gal tanks,
serving different parts of the house, one of which is in the master
bedroom closet.