Hello. I”m the new kid on the block. Building a new one-story home (1657 sq. ft.) in south Texas in the next 12 months. House will use well water, septic tank, & propane gas. I’m considering a tankless water heater & pex rather than copper. Will be using a monolithic slab. Not a large water demand as wife & I are “empty-nesters”. thanks for any
Edited 1/13/2007 5:04 pm by steadyrider
Replies
Welcome to BT. South Texas?
How about a heat pump water heater? Roughly 3x the efficiency of resistance with a byproduct of cool dry air. Ours supplies 50% of our dehumidification needs for 20k cu ft, free (we don't need ac).
PAHS Designer/Builder- Bury it!
SteadyRider:
We have had a Renai for about 5 years now and really love it (it replaced an 80 gallon electric unit). Probably the most annoying problem is that it shuts off completely between uses, meaning, that if you're doing something like washing dishes and turn the water off between rinses, you get a cold blast of water somewhere along the line. That inconvenience is more than offset by the availability of endless hot water (and would probably be a smaller issue if the unit was closer to the point of use). Gas useage is down slightly but probably would be down even more except we now tend to take longer showers since we don't run out of hot water anymore. You can set the water temp to your desired temp, turn on just the hot water and not worry if somebody else flushes the toilet. And as long as you are in the shower, no one else can change the water temp and scald or freeze you.
BILL
Interesting comments on the cold water flashes, I've read about that in other posts as well. I'm also thinking of having the Rinnai installed my home remodel. I take it that the cold water slogs are because there is no recirculation system? I'm thinking that putting in a recirc system in with motion sensors or manual switches or timers would solve the problems of intermittent use and also save water.
Some time back a Boston plumber posted the most interesting comment I have seen on this subject. His analysis led him to the conclusion that a central tank (gas or electric) kept at the ambient indoor temp (70 F 20 C) would allow the installation of lower capacity "on demand" units at the point of consumption. The end result was that the hybrid was more efficient than either a totally central or a totally dispersed solution.
I have had direct experience in Europe with on demand water heating, it is effective and makes perfect sense in a high fuel cost environment. Also very common in Europe are time of day heaters to take advantage of variable pricing (lower at night), central tank based. Of course if your water comes out of the tap near 70/20 all bets are off. Cold flashes I have not experienced, probably because the heaters have less than 8 ft. of piping from heater to outlet. As fuel costs rise tankless will dominate in my opinion.
The old water slug is caused by the fact that the heat exchanger inside the rinnai cools much faster than the hot water left in the pipes (our PEX tuing) by the previous usage. So if someone in your family uses hot water five minutes or so before you take a shower you'll have plenty of hot water to start with but at some point there will be the little bit of cold water that got out of the Rinnai's heat exchanger between the time you turned on the hot water and the burner fired up and started heating. It could be a very small amount but you would sure notice it. Immediately after the slug passes it goes on to be wonderful everlasting hot water with very dependable temp output at between 5 and 8 gallons per minute.
A simple solution to this is to have a small electric water heater receive hot water from the rinnai. My wifes house (that I built for her before we were married) had one small tank in the closet next to the master bedroom and another small tank in the kitchen. It was like instant hot but also endless hot and that Rinnai also heated the floors.
If you are having temperature fluctuation problems with a Rinnai generally that will go back to a clogged intake filter at the bottom of the unit. Look right where the cold water goes into the bottom and there will be a little light brown plastic filter hoder. Cut and drain the water pressure and you should be ale to unscrew it with a big flat screw driver or just your bare hands, it's an o-ring seal so it's not very tight. I've had to use an old tooth brush or a pocket knife to clean that thing out. once it's clean the Rinnai will still have a slight pressure drop,about two feet of head differential between hot and cold and a top flow rate of five to right gallons per minute but it will put out a very steady temp output as it has both a modulating burner (fron 15,000 BTU to 198,000 BTU) and also an electronically controlled tempering valve.
I'm a licensed plumber and a certified Rinnai installer and I've had a huge amount of success with these things and recommend them highly. Only thing is it is true that it will not save you money on gas because you will never have to cut a shower short because you ran out of hot water so you'll end up enjoying longer showers. To me the luxury of endless hot water is worth it.
I have a solar water heater at my place that stores 120 gallons of hot water that the Rinnai brings up to final temp for showers. To my knowledge the Rinnai is the ony one that will allow you to pre-heat with solar. It takes the temp of the incoming water and adjusts the burner to put the output temp where you set it with the electronic controller.
Mine also heats three zones of radiant floor in my office, guest bedroom and workshop that are not heated y my heat pump (and it also heats the hearth stone on my fireplace so I have a warm place to hang out in the evenings while I'm building the fire)------------------
"You cannot work hard enough to make up for a sloppy estimate."
I'm just surfin' subjects and came across your comments on tankless water heaters and I love the common sense approach you have plus the pre-heating option you're using. I can't believe how the interest in the tankless market is going sideways because so many folks that I talk to are hearing horror stories (without substantiation) about inconsistent hot water supply, cold bursts and slow light-ups of the burner. Thanks for adding your comments to the discussion.Cheers,
Ken"They don't build 'em like they used to" And as my Dad always added... "Thank God!"
ShelterNerd,
You have experience with Rinnai.
I am considering locating one inside my laundry home. Is noise a problem?
Any problem locating it high on the wall above the washer?
They do make noise. Enough to not locate one in a bedroom, not a problem in a laundry. High location is only a problem with respect to the exhaust vent location on the exterior of the building. Ther are very strict limitations re: distance from roof over hang above the vent. If you are going through the roof should be no prob. Your local inspector may want you to have access for service but ability to work off of a step ladder in the laundry should be fine. Limitations for compustibles to either side and in front are on the order of six inches or so, our local inspector likes us to put them in a plywood box to keep folks from stacking blankets up against them. Door to the box needs to be on spring loaded screen door hinges to keep it from being left open. I think this is something he made up but I don't fight with inspectors about piddly stuff like this. Remember to get your pop-off valve piped to a safe location with an air gap. All the bestMichael------------------
"You cannot work hard enough to make up for a sloppy estimate."
Michael-
I just wanted to commend you for your excellent website. I looked at it when you posted the link a little further up the page, and started reading about your soapstone stove- there's some great stuff in there.zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
Thanks, it's been a big project putting it together and it keeps gaining momentum. I hope to add lots more to the Green Construction Details in the near future.All the bestMichael------------------
"You cannot work hard enough to make up for a sloppy estimate."
Hi ShelterNerd,Thanks for the insights into the Rinnai system. I haven't actually had it installed yet. My remodel is still in the framing stage. Instead of small hot water heaters, I'm thinking instead of a recirculation system with a timer and remote switch. I will also be having a solar water heater installed to augment the system. Solar water heating seems to be the best bang for the buck for solar!
Jointerman
Watch out with hooking up a recirculating system to a Rinnai. You don't want to constantly circulate water through the demand water heater because it can only modulate down to 15 KBTU. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
I just returned from the National Green Building Conference and a lot of folks there were wanting details on how we do this Rinnai set-up and many others (our 7.5 CFM per occupant make-up air detail, Variable Speed Zoned BYPASS HVAC design, tented (not sealed) crawlspaces, etc) So I'm committing to posting more of those details on my website. Hopefully they will be of help to others just getting into high performance building.All the bestMichael------------------"You cannot work hard enough to make up for a sloppy estimate."
Edited 4/7/2007 12:12 pm ET by ShelterNerd
You realize Michael, that we're going to have to refund the breaktime users $2 of the $8 cover price when they pick up issue #191 to re-read your article -- the one you're giving away here! You also realize, I'm sure, where the $2 each will come from, right?
The ol' bass fund, bubba...
Goodbye Fender, hello HarmonyDan MorrisonAssociate editor
Oops, I figured your excellent editing and a detailed material list and side bar review of D-mand vrs Laing, Grundfos, and Taco recirculating hot water schemes would be worth the addidional two bucks.
Ah well. such is life. Good hanging with you at the green building fest. Now you and I need to chase after Ray Tonjes down in Austin and I'll see if we can bring the evil Troll Brothers to the green side.------------------
"You cannot work hard enough to make up for a sloppy estimate."
I have a solar water heater at my place that stores 120 gallons of hot water that the Rinnai brings up to final temp for showers. To my knowledge the Rinnai is the ony one that will allow you to pre-heat with solar. It takes the temp of the incoming water and adjusts the burner to put the output temp where you set it with the electronic controller.
I have an aquastar 125BS model which modulates its flame down to zero if the incoming water is hot enough. When I bought it 6 years ago it was the only tankless that could do it. Does your rinnai also do this or does it modulate its flame down to some lower fixed value? I want to install a beefier tankless in our new place and would love the rinnai if it actually modulates its flame down to zero. Can you please tell me which model number you have?
thanks,Daniel Neuman
Oakland CA
Crazy Home Owner
The Rinnai only modulates from 15,000 BTU to 199,000 BTU. We use it with a pump that fills a 12 gallon tank with hot water and then we run the recirculating system off the 12 gallon tank. This way we keep the velocity of the water through the Rinnafast enough to use 15,000 BTU------------------
"You cannot work hard enough to make up for a sloppy estimate."
With the solar pre-heated water don't you run the risk of seriously overheating the water? What if the water coming from the solar heater is already at 130degF and then the heater puts another 15,000btu into it? Do you have a tempering valve after the heater or something?Daniel Neuman
Oakland CA
Crazy Home Owner
Yes we do run a tempering valve between the tempering tank and the house, but actually the Rinnai does modulate down to zero in that it will actually keep recirculating hot water at 130 degrees even with a fairly high intake I think it takes a 15 degree differential to fire the burner. IE 110 degree water will be heated up to 130 degrees and 115 degree water will pass straight through to the best of my knowledge. BUT running the heater at very low firew for long periods of time will create a sooty condition in the burner and will eventually damage the air flow and lead to shut down. (voice of experience) so I use the tempering tank to assure a higher BTU demand and a cleaner combustion. It also works well with getting rid of the cold water slug and the way we plumb them we can get short term flow rates of higher than the Riannai will support (ie greater than 8 GPM) and less pressure drop between hot and cold. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
Our architect is recommending the same set up that you have, a solar water heater with the Bosch Aquastar 125BS. But one thing you mentioned that is a concern to me is the want to install a "beefier" unit. We frequently have house guests and even friends relatives living with us for months at at time and I'm concerned that the 125BS won't be able to deliver two showers at a time. Is this to what you are referring? I think that I've seen the Takagi T-M1 is solar compatible. Maybe Shelternerd can give us some insight on whether the Rinnai units might be the better choice?BTW: We're building just across the bay from you in Mountain View, CA.
In my experience the 125BS can not deliever two showers at once. But I've never ever lived anywhere where the water pressure was strong enough and the water heater strong enough to do that...maybe if your house was plumbed manifold style with valves at the manifold and you had pretty high water pressure. Our water pressure at the hose bib nearest the meter is ~32psi...not so high.
We are not solar pre-heating the 125BS...we had always intended to but never got around to it. Our ground water here is ~55degF so if your solar pre-heater can get the water up to say 80deg F in the winter you should be fine with two showers. In the summer I would imagine that the solar hot water heater would be enough and the 125bs would not need to fire at all.
I want a bigger unit for our new house which is three stories and three full baths and I am not sure if solar pre-heating will be an option there.Daniel Neuman
Oakland CA
Crazy Home Owner
Here (if I did it right) should be two images that will help you out. I'm working with my web guy to get it posted on my site with more detail this weekend and probably will continue to edit it over the next few weeks to ad recommended parts lists and sources for parts. So this will still a rough draft for a little while. Try checking http://www.ChandlerDesignBuild.com next Wednesday or so and look in the portfolio section under Green Construction Details. I'm just starting to populate that part of the site but this will be next followed with a discussion of how best to meet Energy Star and GBI's mandate of 7.5 CFM per Occupant balanced make-up air. I'm off to the National Green Building Conference in St Louis in the morning. A shelternerd's idea of a good time!All the bestMichael------------------
"You cannot work hard enough to make up for a sloppy estimate."
Hello Michael,
I am new to it all. (message boards, building, green, etc) Would you mind revisiting the Rinnai subject?I have read all around, become totally discouraged with trying to build anything other than "conventional" and then get re-inspired by someone like you and your "family"I am on the home-stretch building a steel 60x80 hangar in Rosamond, CA outside Edwards AFB. The temperature is at the extreme ends depending on the time of year, but we almost always have sun. I have 400 sq ft of dwelling on a upstairs mezzanine. The apt may be used only on weekend or full time. Probably 1-2 people but I would prefer to be prepared for simultaneous use of the shower, sink and laundry.Solar could probably provide enough hot water much of the year but I am guessing the ground temperature gets pretty low in the winter, and the unit is planned to be down stairs in the unconditioned hangar. I have put in PEX, any problems there?What type of solar panel and accessory tanks are you using? Would you be willing to make an estimate of material cost?Please tell me if all these questions are beyond the scope of this site.Thanks, Pam
I've read in many places that it's also a good idea to filter the water before it enters the water heater. It's supposed to prevent mineral buildup on the interior of the water heater.What kind of airplane do you have (N971TA)?
Oh good idea. Maybe just an inline?
No plane, yet. I was running short of patience when the names I might remember were all taken. So in desperation I defaulted to the Skyhawk 172 I usually rent. And you? or would that be a woodworking use of "plane?"
I plan to do a whole house filter in the house I'm about to finish.I'm also installing a Rinnai model 751. According to their website it should be able to heat two showers simultaneously during our Middle TN winters. I contacted our local water company and was told that the coldest our wintertime water gets is around 43 degrees. Using that info I consulted a chart on Rinnai's website that, when combined with your maximum flow, shows you which of their models can keep up with your demand.Rinnai also claims that because of their ability to "modulate" their heating, many of their units are compatible with circulating pumps as well as solar heat collectors. What I find interesting about this claim is that, if memory serves me correctly, only one or two of their units have a 10,000btu minimum. Most have 25k or more. I don't have enough knowlege on the subject to know if the low flow of a circulating pump would be enough to start the heating on any of those units. Michael Chandler, a previous contributor to this thread, is really the guy to ask about this. He wrote a nice article for FH on this very issue. I seem to recall he has some more current info on the subject on his website. http://www.chandlerdesignbuild.com/ As to the issue of cold water slugs...that was the primary info provided on Michael's article. However, I was told just a few days ago by a guy from our local NG company that installs hot water heaters for them that Rinnai's newer units have temperature sensors located throughout their units. He claimed that the purpose of these sensors is to detect if the water is as hot as the desired output temperature called for with the remote control. If it isn't, supposedly that water is recirculated within the unit itself for a second or two until the temperature is reached, then is sent out of the unit. I am somewhat dubious of his claim since nothing on their website indicates such a feature. I haven't had the time to contact Rinnai to quiz them about it either.My full name is Steven Patrick Lane. I became interested in flying when I was very little so the username is perfect in more ways than one. I don't own any but I'd like to race F1's at Reno one day. I'm also currently building and Harmon Rocket/F1 Rocket hybrid that I hope to complete in the next 8 years or so. (My youngest graduates then) I've done some introductory aerobatics you can watch at http://www.myspace.com/stevenplane. I was this close to taking those lessons with Bill Kershner but unfortunately he passed away. His plane is now in the Smithsonian. I ended up taking lessons with his protege', Catherine Cavagnaro.
Why would you size a tankless based upon how many showers can be done at the sme time?
Is that how you plan on using it?
I have kids....nuff said.
Then a tankless may end up increasing your gas bill.
Then a tankless may end up increasing your gas bill.
Why? We won't be taking any more showers.
We just have occasions, usually every other weekend when my daughters are visiting, when several of us want to take a shower at approximately the same time. With a 40 gallon NG hot water heater we can take two showers in succession but then have to wait, sometimes 30 minutes or more, for recovery to allow another shower. With 5 people total, a clothes washer, and dishwasher, this occasionally ends up being more inconvenience than I want to deal with.
The other 26 days of the month there are only 3 of us...actually, 4 of those 26 there are only two of us.
Even if it does cost more (I have no idea why you would think that it would) I will happily pay for the convenience it allows.
Come back in a year and report in.
I might be able to sooner. It's the only gas appliance we have. Each month our gas bill is almost the same as the month before, very consistent.
I will be curious to find out.
People often tend to take longer showers when they know they will not run out of hot water.
I've used tanks (30, 50, and dual 50's), assisted production (from a GSHP) and tankless in between.
None of us are the long shower type. We get in, do our business, and get out.
The only time I've been without enuff water is when one of the elements is bad or there's too much sediment in a gas model.
The best efficiency has come from the GSHP. Next is a smaller tankless coupled with behaviorial changes such as cold water hand washing and using multiple hot water appliances at the same time.
But for a spoiled wife, those changes don't come cheep.
Happy wife, happy life I always say.
Tell your wife that cold water is less drying to the skin (it really is!). Maybe that would sway her.
John
With a tankless, one really doesn't have the choice. You gotta sit and wait for the hot water to clear the lines - every time. And when doing so, all of that heated water in the lines goes to waste.
A recirc would be best, but not green. That small preheater tank sounds good.
does it cost about $90 a year for standby losses in a TANK model? Seems to me the first time you have a service call on the tankless when its computer dies (unavailable at lowes on a weekend or any other time) that service call will pay a years standby losses on a tank????
I'll attest to that, I am getting ready to put one of these in my teenagers' shower. We are in drought billing based on average use. I have to go bang on the door to get them out.
http://showermanager.com/
Mike
Small wheel turn by the fire and rod, big wheel turn by the grace of god.
This is a very good rec.
My father's bosch unit would 'silt up' often and need to be flushed backwards, restoring its capacity until he filtered in incoming.
pat
A filter won't help with dissolved minerals in the water.But it does help with "dirt" which is more common that one realizes..
William the Geezer, the sequel to Billy the Kid - Shoe
Very sorry all...I had Rinnai on the brain. The tankless model our local NG company deals with is Noritz.
That's the manufacturer I intended to refer to.
Well after a couple supply house visits and a weekend with Google....
Rinnai RR50LSIN looks more expensive, but the Takagi T-KJr distributor was exceptionally unfriendly and said he would sell me the unit but would not tell me the price because it would take too long to look it up.
Rinnai apparently does not sell a damper or whatever it is called that will prevent the wind from blowing sand back into the exhaust outlet. I am concerned about that, as the unit will be exhausted on the west "windward" side of the building, where we get some pretty good winds coming across the desert. Any thoughts?
Is it reasonable to re plumb for a holding tank or solar later if needed? The unit will be below the apt in the relatively open hangar area. I would really like to save the expense for now if possible.
"My wifes house (that I built for her before we were married)"LOL is that what it takes to seduce a good women nowadays.BTW have you ever heard of or used one of these:
http://gfxtechnology.com/contents.html#selection
I've heard of those things and I can see where they would make sense for pre-heating the cold water heading into a shower but I look for the low hanging fruit on energy conservation and the drain heat recovery units seemed kind of marginal to me compared to air tightening and enhanced wall and roof insulation so I've never used one.I'm going to get my web dude to post my piping layout for recirculating hot water on a Rinnai on my website this weekend, I'll post a link once it's up. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
This is a common question and if you search the archives you'll find an hour's worth of reading, both pro and con.
My personal experience was that it didn't save much money (I made calculations on actual savings after I installed one). The payback in dollars was over 10 years, and the annoyance of the quirky flow wasn't worth the tiny savings. The unit broke three times in the 7 years I had it, and the final time it broke the dealer couldn't fix it. Since it didn't even last the 10 years it cost more than it saved, not even taking into account the repair costs.
I'd recommend something else, even a smaller (say 30 gallon) conventional water heater.
WL5, Much thanks for your input. May I ask what brand you had and was it a gas or electric model? Also was it installed on the exterior or inside the house? smrsstx. smrsstx
It was gas, installed indoors. I don't remember the brand, it was something like Aqua Star.
If you decide on tankless, now is a good time because you can design in extra-large gas lines (consumption can be 175,000 BTU/hr), proper flue placement and length (expensive ss positive pressure flues and very hot exit temps) and WH placement as close as possible to the major hot water usage areas (baths and kitchen) in order to minimize heat loss due to pushing a big slug of cold water through the lines.
With a well water supply system, as the pressure changes from high pressure pump off setting to low pressure, pump on, (typically 20 psi) you will notice signifcant changes in the mixed water temperature. The pressure drop through a tankless water heat is greater than tank types. As the water pressure changes, the flow changes. Most tankless water heaters have a constant temperature output control and do a very good job of modulating the gas valve to maintain a constant outlet temp. The difference in hot water flow at a constant temp is greater than the change in cold water flow at a constant temp due to the greate pressure drop through the tankless unit, making for a shower temperature that constantly fluctuates. Enough that I replaced mine with a tank. My tankless is now the heat source for garage infloor heating system. Energy issues aside, something to think about.
Even though these units can respond very quickley to transients, not quick enough to prevent the cold or hot "slugs" that will occur when any other water tap is opened while your in the shower (or whatever).
BTW, the energy savings is not enough to pay for difference in price in over the course of 10 years (as I calculated it in my specific case). Your mileage may vary.
Unless a unit is dedicated to a specifc area of the house and segregated from other hot water demands,. I would never consider one again.
Tim:
I have to admit that I never have had that problem. The Renai that we use has controls that allow you to set the output temp specific to the task at hand (110 for a shower, 120 for laundry or 140 for dishwasher for example) so when I am in the shower I just crank the shower valve all the way over to hot and let the tankless regulate the temp. Never had a problem with varying water temps.
BILL
I started looking into tankless systems for a remodel, which would be unused much of the time. As such, it made sense.
The first thing I learned was gas was the only way to go for heating large quantities of water.
Second, I had had to look real close at the well water temp. The remodel had very cold water. That meant you had to work a lot harder to raise the temp.
Third was "how much water would be used at a given time."
Next, there was the cold water start problem someone else mentioned. This can be addressed, somewhat, by your PEX system. Home runs with smaller lines will get the hot water there faster, but you don't want such small lines you cut pressure.
Finally, we started looking at the system using PVC for its exhaust. It transfers so much heat to the water, you didn't have to go to metal or insulated pipe.