Installation of Tankless Water Heater

[jmen24]

dpg
You are correct in that is costs more to make hot water than it does to maintain hot water, but a fair amount of our clients only come up a few weekends out of the year and that includes winter and they typically shut down the water system to prevent massive flooding in the winter if the system has a freeze up. In those situations we recommend the tankless, as the hot water is right there when then come up and want to have a shower right off.

[Mee-n-Mac]

Originally Posted by jmen24

dpg
You are correct in that is costs more to make hot water than it does to maintain hot water, but a fair amount of our clients only come up a few weekends out of the year and that includes winter and they typically shut down the water system to prevent massive flooding in the winter if the system has a freeze up. In those situations we recommend the tankless, as the hot water is right there when then come up and want to have a shower right off.

Huh ? I think it costs less to make the hot water than it does to make and maintain it, which is what your typical system does. Am I missing something here ? If you're constantly using the hot water then the difference may be small and not enough to make the extra cost of a tankless system pay for itself. We'd have gone tankless except that the plumber guy said the gas line (from the LP tank) would have to be redone as the on demand systems required more flow to make the BTUs they do. This made some sense and then again .... How many more BTUs, say over a gas range, does a typical 3 GPM tankless system produce (note: not used in winter) ? What kind of "special" pressure regulator and gas line diameter (if any) does an on demand system need vs a typical tank system ?

[jmen24]

Originally Posted by Mee-n-Mac

Huh ? I think it costs less to make the hot water than it does to make and maintain it, which is what your typical system does. Am I missing something here ? If you're constantly using the hot water then the difference may be small and not enough to make the extra cost of a tankless system pay for itself. We'd have gone tankless except that the plumber guy said the gas line (from the LP tank) would have to be redone as the on demand systems required more flow to make the BTUs they do. This made some sense and then again .... How many more BTUs, say over a gas range, does a typical 3 GPM tankless system produce (note: not used in winter) ? What kind of "special" pressure regulator and gas line diameter (if any) does an on demand system need vs a typical tank system ?

You have to remember you are making the hot water in both cases to begin with, its the different of maintaining or constantly making. A modern day stone lined water heater will hold the heat in the water for an incredible amount of time, the $200.00 units at big box stores, not so much. Just about every manufacturer of Tankless water heaters states in there product brochures about the need to pay attention to usage (almost all recommend a dedicated system for dishwashers or large soaking tubs), Rinnai has a section in there site that will actually calculate the size or number of units needed based on zip code. In our area the ambient temp of the incoming water has to be heated to a certain degree for comfort, tankless units (within the spec sections) will give you the output temp at certain GPM's (what your faucet is rated for at max output), add this to the incoming water temp and that is what you can expect at the tap. You then need to size the unit appropriately based on need.
On Rinnai's site when you plug in your information, as an example I plugged in a local zip, 3 baths, 5 shower heads (hand helds with fixed in two units) and two of the units being tub/shower combos. The result was to contact a local dealer as more than one tankless unit would be required. That gets expesive quick and there is nothing stating how many faucets being used at once, but your usage needs to be based on total possible output.

The total cost of energy used goes beyond the gas being burned to heat the water and store, but electricity used to run the well pump, circulators, etc. This is exactly what the LEED construction points are based on, not how "green" one item is but how everything works as a total package and most the "green" products that are marketed as such are not so when added into the big picture.

As for regulator and line sizing that is a question for a qualified installer or manufacturer, its a basic physic calculation but they use software to prevent the headaches. I am just a Project Manager that has a particular interest in researching and educating myself on new and old construction practices. Contact The Granite Group and talk to someone in retail sales (not the counter) they would be able to tell you the line sizing and regulator needed for a particular system.

The btu question is a little easier and a little complicated, all manufacturers post btu ratings for gas appliances, the 3GPM btu rating for a tankless will vary depending on model. 3GPM on one model will be different on another, because a larger unit can heat water hotter at 3GPM than another. You have to remember that the water at no point in time is stopping to be heated, so it has to absorb as much heat as it can as it passes through the heat chamber, the faster it moves the more energy is required to get heat into the water.

These long posts are killing me, sorry for the technical long winded explainations, hopefully I am actually answering your questions.

[BlackeyCoveR]

I did the same comparison and ended up staying with the electric water heater. I looked at overall energy consumption, and volume of water we need (family of 5 plus frequent guests).

Although we're at the lake most of the summer, off season not so much. So with electric, I hit the breaker every time we leave and draw no electricity. I was not able to shut off if I went with gas.

[hazmatmedic]

I can help with the line sizing and regulator. Most regulators provided by your lp supplier will handle the increase in the btu load of the Rinnai, but if it didn't, they would provide a higher volume regulator for your needs.

The line size is a different story and thats why having your propane supplier provide the Rinnai and installation of that product is probably the most cost effective, because they can do the whole job. Still get a quote from your supplier. The line size calculation isn't as complicated as Jmen24 leads you to believe. The NFPA code books provide that info or most technicians have a handy pocket sized book with the info. The Rinnai recommends the minimum of 3/4" IPS (iron pipe size) for propane supply, but that may have to be increased if it is a long distance from the point the gas supply enters your home.

The other questions regarding line size was standard gas H2O heaters and gas ranges. "Typical" gas ranges are @ 60,000 btus and "typical" H2O heaters are @ 40,000 btus. The standard Rinnais are @ 200.000 btus and this is why it requires a larger line.

The on-demand water heaters are not really for larger homes (more than 2 bathrooms), but are really ideal for smaller second homes. That is based upon some of the information that was provided by Jmen24.

[jmen24]

Thanks for the line sizing info. I do not feel qualified to list line sizing and regualator sizes as I am not an installer, I leave those requirements to the specialized pros.

I want to make sure that I am clear in not selling one unit over the other, the tankless systems are very good, just make sure it fits your lifestyle and needs.

[John E]

I can't see any reason not to use the Rinnai aside from initial cost. I'm wiring a large condo project and they are using the Rinnai as their choice of water heater. 2 Bed/ 2 bath units.

[wifi]

200K BTUs... Yikes. Wonder if you could put a heat exchanger on it to recover some of the heat for the house/basement or what ever?

[ishoot308]

I'm having a Rinnai installed in my camp in a week or two and will report back as to it's effectiveness. I have a couple of friends who have snowmobile camps in Pittsburgh New Hampshire that use Rinnais and absolutely love them. I have rarely, if ever, heard anyone who has a Rinnai say anything but positive comments. Hopefully I will be the same!

Dan

[jmen24]

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]

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]

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]

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]

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]

Jmen24

Thanks for the clarification