Installation of Tankless Water Heater

jmen24 · 05-07-2009, 11:01 AM

Rinnai is one of the easiest companies to work with regarding any issues, if you have them. They are a good choose if you are thinking of installing any type of system that they produce, tankless, monitor, etc.

upnorth · 05-07-2009, 01:04 PM

We also installed a propane-fired tankless heater and I love it. Water is very hot and we've never run out -- even with multiple simultaneous showers.

The builder recommended we go tankless and the cost differential over a propane fired hot water heater was only $170. Interestingly, when we tried to estimate what level we ought to be for propane pricing (per the deal with Our Town and Eastern propane) -- this being our first year with a new house -- the customer service rep commented that the Rinnai Tankless is very efficient and hardly enters their calculus. On the downside, every single time the hot water is turned on at the faucet for even a moment, the tankless fires up and you can hear it in certain areas of the home -- I'm sure I'm the only one that notices...

I do notice a delay, but it's really not that long, maybe 30 sec?

Island-Ho · 05-07-2009, 01:24 PM

I would hope that the unit is designed so that a very high percentage of that 200K BTU goes into heating the water and that there is very little wasted to recover for space heating, although you might get a little out of the vent flue.
I am considering using a tankless heater downstream from a solar hot water system. Does anyone know if the Rinnia fires up based on incoming water temperature or simply turns on when the water starts flowing? Obviously the second scenario would be undesirable if the incoming water is already hot enough! Currently my solar heated water flows into a backup gas fired water heater, but I would like to eliminate having to keep that tank warm all the time when there is plenty of solar heated water available.

wifi · 05-07-2009, 01:57 PM

BTU = heat required to raise one lb of water 1 degree F
Water weights about 8 lbs/gallon.

Lets guestimate we start at 50 degrees and want to get to 120 degrees. This is a 120-50=70 degree rise times 8 lbs/gallon = 560 BTUs to raise one gallon of water from 50 to 120.

So, 3 gals/min = 1680 BTUs/minute times 60 minutes = 100,800 BTUs per hour. Efficiency is ~50%?

Hmm... where am I wrong ?

jmen24 · 05-07-2009, 03:54 PM

Quote:

Originally Posted by wifi

BTU = heat required to raise one lb of water 1 degree F
Water weights about 8 lbs/gallon.

Lets guestimate we start at 50 degrees and want to get to 120 degrees. This is a 120-50=70 degree rise times 8 lbs/gallon = 560 BTUs to raise one gallon of water from 50 to 120.

So, 3 gals/min = 1680 BTUs/minute times 60 minutes = 100,800 BTUs per hour. Efficiency is ~50%?

Hmm... where am I wrong ?

Its 8.34BTUs for 1 gallon of water, but that is only skewing a little.

The 200K number I believe is arbitrary. Linked is one of the smaller units Rinnai makes and we use this for discussion http://www.rinnai.us/documentation/d.../V53e_SP-1.pdf It has a rating of .82 so, 82% efficient with a max output of 120K BTU with max flow of 5.3GPM. If you look at the graph, for 3GPM requires 98400K BTU (actual output being transfered into the water) to achieve approx. 60 degree rise in temp with 21600K BTU being lost. Obviously, this unit would not be sized properly, but it works for the point.

The 200K BTU model would not be using the full max output to achieve that rise in temp it would only be using 121K BTUs with a loss of 21K BTUs.

These units use a ambiant temperature sensor to determine output BTUs needed based on call demand.

wifi · 05-07-2009, 06:17 PM

Jmen24

Thanks for the clarification

05-07-2009, 01:04 PM	#2
upnorth Senior Member Join Date: Jan 2005 Posts: 64 Thanks: 0 Thanked 2 Times in 2 Posts	Copied from my post a few months back... We also installed a propane-fired tankless heater and I love it. Water is very hot and we've never run out -- even with multiple simultaneous showers. The builder recommended we go tankless and the cost differential over a propane fired hot water heater was only $170. Interestingly, when we tried to estimate what level we ought to be for propane pricing (per the deal with Our Town and Eastern propane) -- this being our first year with a new house -- the customer service rep commented that the Rinnai Tankless is very efficient and hardly enters their calculus. On the downside, every single time the hot water is turned on at the faucet for even a moment, the tankless fires up and you can hear it in certain areas of the home -- I'm sure I'm the only one that notices... I do notice a delay, but it's really not that long, maybe 30 sec?

05-07-2009, 01:24 PM	#3
Island-Ho Senior Member Join Date: Apr 2004 Posts: 178 Thanks: 21 Thanked 14 Times in 11 Posts	Comment & Question I would hope that the unit is designed so that a very high percentage of that 200K BTU goes into heating the water and that there is very little wasted to recover for space heating, although you might get a little out of the vent flue. I am considering using a tankless heater downstream from a solar hot water system. Does anyone know if the Rinnia fires up based on incoming water temperature or simply turns on when the water starts flowing? Obviously the second scenario would be undesirable if the incoming water is already hot enough! Currently my solar heated water flows into a backup gas fired water heater, but I would like to eliminate having to keep that tank warm all the time when there is plenty of solar heated water available.

05-07-2009, 01:57 PM	#4
wifi Senior Member Join Date: Jul 2007 Location: Lakes Region Posts: 1,321 Thanks: 282 Thanked 287 Times in 169 Posts	This ought to be easy to figure out BTU = heat required to raise one lb of water 1 degree F Water weights about 8 lbs/gallon. Lets guestimate we start at 50 degrees and want to get to 120 degrees. This is a 120-50=70 degree rise times 8 lbs/gallon = 560 BTUs to raise one gallon of water from 50 to 120. So, 3 gals/min = 1680 BTUs/minute times 60 minutes = 100,800 BTUs per hour. Efficiency is ~50%? Hmm... where am I wrong ?

05-07-2009, 11:01 AM	#1
jmen24 Senior Member Join Date: Feb 2009 Posts: 1,139 Thanks: 223 Thanked 319 Times in 181 Posts	Rinnai is one of the easiest companies to work with regarding any issues, if you have them. They are a good choose if you are thinking of installing any type of system that they produce, tankless, monitor, etc.

05-07-2009, 06:17 PM	#6
wifi Senior Member Join Date: Jul 2007 Location: Lakes Region Posts: 1,321 Thanks: 282 Thanked 287 Times in 169 Posts	Jmen24 Thanks for the clarification