Stop me before I over think this!

The concept of a tankless water heater appeals to the titewad in me. However most I’ve seen lately cost a grand or more! (six in the family so far) Now my water heater is over 22 years old so it’s on it’s last legs and I have no doubt that when I move it next month that will be the final death of it..
Can I consider replacing a 50 gallon gas water heater with a tankless?
Which brands? I’ve seen several offerings by Rheem and one by Bosch but the Bosch doesn’t have a good reputation locally.
Is 199,000 BTU’s enough? are we possibly talking two units?
Replies
Just some things to consider....
1BTU will heat 1 lb of water 1 degree F. Considering how quickly the BTUs add up when you have to achieve a Delta-T of 80, you can see why storage-based water heaters are as popular as they are...
Now go through all the fixtures you can expect to be on at a given time and see if you tankless can cover them. Then verify that the tankless will also work if only 1 fixture is calling for hot water...
Me, I'd always go for an indirect, but that presumes a hydronic-heated house.
Lastly, as the spikey demand of tankless water heaters makes itself known to the gas distribution networks, expect them to retaliate with peak demand pricing. It's just a question of time, IMO. Not an issue if you're on LP, of course.
How did you get a 22 year old water heater in that new timberframe? And you're moving a furnance, too?
Wazzup with your designer/archy?
peteschlager,
The stupid ignorant designer tears down a portion of the old house and then builds a new timberframe. Sure would have been about a ton easier if he'd been able to talk the city into allowing him to start from scrtach but for a whole lot of reasons that's what the city requires..
I'll tell you if I didn't work so cheap I'd fire my butt and get somebody who knows what they are doing on this project!
I mean a double timber frame? what am I doing? building a bomb shelter?
!6 inch thick walls and 22 inch thick foundations?
I mean a double timber frame? what am I doing? building a bomb shelter?
!6 inch thick walls and 22 inch thick foundations?
I always thought that was to keep the skeeters out. Flew into Mlps yesterday from Fargo - y'all sure have a lot of breeding grounds there! Guess lakefront property isn't such a big deal though - you sure have a lot of it.
Hijack over...
IMHO,
The advantage of a tankless is very slight given the minimal standby losses of modern tanks.
I would expect that 199BTUs should be enough for about 2 concurrent showers, depending upon flow.
Frenchy--
We put in a tankless--Noritz DV84. Love it. We replaced 50 gal. tank. It provides enough hot water for a family of 5 (two showers and dishwasher at once). This model does 236K btus, I believe.
Expensive? Yes--about 2-3 times the cost of a good tank. But the advantages are great:
The drawbacks are:
I say, "Do it!" (It's not my money :-0 )
Edited to add: I'd stay away from the Bosch and look at Noritz, Rinnai, and Takagi.
Edited 5/30/2006 11:22 am ET by Pnut
Pnut,
you gave me extremely great information, thank you!
The brands you recommended, how popular are they? I get near free maintinace service from my gas company but if they don't have access to the parts the delay can be extremely long.. What sort of long term maintinace issues do you expect to occur?
Frenchy--
I know Noritz and Takagi have websites and you can do a "dealer locator" in your area. I bought the the Noritz from a "real" plumbing supply house--most of the good plumbing stores carried one or the other brands.
While I was in the store, a number of plumbers said how much the liked the unit. One said it would be the last water heater that I would buy--as they tend to outlast tanks by a considerable time...I don't expect the need for servicing any time soon...and if does need work, I think most of it I could do myself. Installation was relatively easy--I had a plumber bring gast to the unit, but hanging it and venting was pretty straight forward.
Tankless water heaters are not new technology--it has been around for decades. The Noritz and Takagi are both made in Japan (actually built in Japan). They are very well constructed, and are relatively simple in design. They have some electronics, but most of that is "outside" the mechanical "box."
I think those that have purchased them in the past, and now are complaining, have bought inferior products and from those companies that are new to tankless water heaters. I think if you do your homework, purchasing a tankless water heater is the biggest no-brainer in the history of mankind. I've had "buyers remorse" on a few products but the tankless is not one of them.
For me, I'm concerned with a quality product that is going to last and provide a return on investment. Right now, I wouldn't trade my tankless for any tank product no matter what the cost differential.
Here's some pretty pictures to entice you:
View Image
View Image
When you first turn on the hot water, in let's say a shower or to rinse the dishes, how much cold water runs through the lines before the hot water gets to the faucet?
I have a big concern for the amount of cold water that is just going down the drain until the hot gets there. Would the cost of that water going down the drain equal the amount of savings one might think your getting from reduced energy costs and make it a wash?
BjR
BjR,
wouldn't waste water, that is preheated water be the same no matter what unit (tank or tankless) was used? I know that my kitchen which is a long way from the currant water heater takes many minutes to expell the cold water while the guest bath seems to have instant hot water.. (right above the water heater)
It would seem that is that's an issue with you you need to go with a hot water recirculating system.. The issue of tank or tankless isn't really relavant to how soon you get hot water..
Many of the tankless systems used in other countries are actually small point-of-use units. There's a definite efficiency gain to be had from point-of-use vs central water heating (though often not enough gain to offset the loss of economy-of-scale, etc).There actually are a few schemes available to recover the waste heat from water down the drain (and, when you stop to think of it, virtually all hot water goes down the drain, often after giving up less than half of its heat). But there are a number of technical problems to be overcome to make such heat recovery practical.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
It depends on how far the tankless is from the outlet...In our kitchen it is a short period of time, but in our upstairs bathroom it is longer...BUT this is no different than when had a tank...
You could avoid this by putting on a timer and a recirculating system...or put in a smaller tankless near the source of the outlet. We chose to not do either of these...and we do waste some water, but not anymore than when we had a tank. Also, when did our rehab (we are restoring an 1881 Italianate), we insulated ALL of the hot water pipes--which really helped.
Probably won't change your mind, but when I was looking at these last year, I talked to a plumber that I bought a truck from. He was adament that the tankless were not as good as represented. His main complaint was inability to get parts from the foreign manufacturers. Said he had waited days for some, weeks for others. He also said they could be tempramental units (b/c of the computers inside?). He said there was no way he would put one in his own house.
Don K.
EJG Homes Renovations - New Construction - Rentals
Basic cost of units $200 Verses $1200. Cost of install $300 verse $300 to $1000 if new venting or gas/electrical work.Electric units require mondo(very big) electricity. Big wire and breakers. Electrical costs are much higher than gas in most areas.Energy savings approx $5.00 per month so 200 months or 16.5 years to brake even. Your miliage will vary. Please change the numbers to fit your experience.So far, all of my customers who want one only put them in to run whirlpool tubs and or laundrys where the cold start up is not a problem and it is to add to the main water service to service the deluxe amminities. Price is not a factor then.Two standard 40 gallon takes in tandom is the least expensive most servicable and convenient system, if you have the space for them.
I have been living with a Tankless for 5 years. Installed it myself(female).
I love having long hot showers that never run out of water, even when loads of laundry or dishes etc. have been done. No standing pilot light. Only heat what we use. It heats all our domestic hot water and our infloor radiant heat.
We have a remote control that allows us to adjust the temp of the water very eassily. This allows me to adjust the set temp of the water when it is bitterly cold and the radiant could use a bit extra. It also allows someone to lower the temp. when they have kids in the house.
Installation is simple. Ours is propane.
Jill
Edited 5/31/2006 12:48 pm ET by jmagill
Which unit did you go with?
We have a Takagai. We have the smallest unit as we have a small house.
DonK
That seems to be the consensus that I get. Some say they are the best thing since sliced bread while others seem to have countless gripes..
My thoughts are a bit differant..
First I suspect I'm going to use a pair of electric water heaters to run the iin floor radiant system I'm installing.. While virtually everyone reports that a gas water heater is more efficent I wonder,, In that most of them sold here in Minnesota use indoor air for combustion.. Bill Hartmann reports of a model that uses outside air for combustion but it's not sold here for some reason (I'm researching) second the exhaust vent is a direct 4" hole 24/7/365 allowing heat to escape.
Third, electricity isn't terribly expensive here In Minnesota, for the following reasons. We are close to western coal ranges, have several nuclear powerplants, and are starting to get a lot of windpowered generating capacity. Compared to the finite amount of gas available.
IN addition I have a high efficency forced air furnace which I will regulate to a backup role.. That will allow me to undersize the in floor radiant system which generates higher overall efficency without the risk of discomfort due to that same undersizing.. (as a further back up I will have three fireplaces, 2 gas and a wood burner)
If the tankless should prove to be problematicI actually plan on tapping into the electric water heaters and religate the tankless to a back up role..
Complex as that sounds. If you were to visit my house and see the degree to which it's over built such systems would be childs play..
"...electric water heaters... virtually everyone reports that a gas water heater is more efficent I ..."
Only one who has no clue what "efficiency" means would claim that a gas fired appliance is more efficient than an electric one. I have seen some morons post just that, but very few. There are many reasons to prefer gas over electric, but efficiency is not one considered by intellegent folk. The losses associated with electric resistence heating, whether it be used to heat air or water or steel, are such an extremely small fraction as to be infintesimal, i.e. zero. Electric heat is 100% efficient. Gas heat, is at best 94% efficient, and water heaters, with a few exceptions, burn with a combustion efficieny that rarely reaches 80%. Most residential tank units burn in the 65 to 75% range, and tankless units are no different. Comparing AFUE values to combustion efficency is not a suitable comparison, apples to oranges. However, efficiency is the ratio of the effect/power or for the simpler folk, what you get/what you pay for, and in electric resistance heating, that equals 99.999999999/100.
Maybe "virtually everyone" reports that it costs less to heat with gas as opposed to electricity, but that has nothing to do with efficiency.
Tim,
You are correct as stated, however rather than type what you did I simply said more efficent.. I could have said less costly to operate however I don't believe that.. While the actual costs of running a gas water heater may be less, that does not take into consideration loss of heated air up the flue (OK to be technical out the side exhaust)
In addition as I stated in an earlier post Minnesota is blessed by being close to the western Coal mines, has some hydroelectric power plus two paid for nucear powerplants and we are starting to get big into wind power.. Thus I believe that in the long term Minnesota's electricity rates will be competitive.
My state is blessed with a lot of progressive people. We tend to be careful and fiscally prudent while still keeping an eye out for future trends. That is why we have such diverse electrical energy production, why we never sink as low as some states do when the economy falters or rise to the extremes when the economy booms.. Minesota always maintains relatively low unemployment rates and in spite of being stuck up here in the fridgid north we are home for a surprising number of Fortune 500 companies.. In short My state works well unlike some southern states like Texas!
"Cost-efficient" is the most economical precise term.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
And prudence went out the window with the past five years of give-away tax cuts.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Just completed a bathroom refit.Owners compared cost of a new electric tank heater in its new location VS new instant gas system. The difference if any was small so they went with the gas.In the first week of operation they had relatives staying.....8 to 10 people in the house, all having a shower everyday and the new gas kitchen stove was running off the same bottles.They just used up the first bottle after 8 weeks of use. Cost per month.........$25. Electric bill has dropped about 50 bucks a month as well.
Plus they have mains pressure hot water for the shower now instead of the old low pressure. They couldnt be happier.If I recall it was a Rheem unit, sorta standard here.
Not an exponent of the DILLIGAF system.
Where do you get the idea that a tankless will last longer than a tank-type heater. If you check your warrantee it will be no more than 10 years. Just because the advertisements say they are designed for 30 years, you should not believe them. Most tankless heaters are warrantted for only 7 years with a few being 10 years.
Bill
whoover,
It really doesn't matter about the warrantee.. If you look at the materials the tankless are made from the Japaneese, Finish, and serval German models (Bosch excepted) appear to use very high quality materials and the differances is in the quaility of construction..
That's my opinion. I know the materials in My Sears water heater were fairly marginal when I bought it 22 years ago but it's held up well and I haven't even had to replace the anode yet!
So warrantee does not matter....interesting. It is true that the tankless units look nice but it is also true that all the water joints are "0" ring joints and not solder or welds. In addition, since they work very hard when they are one, one would wonder how long the burner assemblies will remain working. Finally, water quality is very important since these things do not work well if you have scaling water...in fact, the warrantee is invalidated if the water quality is not near perfect.
Your 22 year old Sears may have been made with marginal materials in your opinion but since it has lasted more than twice the warrantee period, the facts say otherwise.
Bill
whoover,
In my opinion a warrantee is pretty well useless. Few cover the cost of having the tech out to your house.. None will compensate you for your time.. It's not hard for my time to greatly exceed the value of any warrantee.. In addition for a modest fee My local gas company handles all the maintinace/ repairs on any appliance.
I'm pretty handy, so leaks and stuff are a simple matter at the local hardware store.. buners might be a problem but some of the brands I've looked at seem to have a good following both here and in their native country. The cards will be a challenge, but they are going to be a challenge with acceptable risks.. As I've said the house will be heated with electric tank type water heaters so it's a simple matter to plumb everything so the tank type will act as back ups untill a replacement card is obtained..
As for water quaility my comment about the durability of my currant water heater was really a statement about the water quaility. As I said I haven't needed to replace the anode. Something which normally doesn't last 22 years..
I hope that you experience that long life with your units. Not all I've talked to have been so lucky.+++++++++++++++++++++++++++++++++++++"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
Thank you.
How many in family? what does gas cost per therm? what does electricity cost per kWh?
experianced,
the size will vary, currantly we're at three, soon will be at 5 and then six.. Mpls. has extremely low electric rates (I'll check with she who must be obeyed tonight to find out what they are) moderate Gas prices..
In my opinion a tankless water heater is rarely a "winner" for home use. Better to spend the money on the most efficient tanked model you can find.
A tankless unit must be sized for the max hot water needs in the house. (Eg, how many showers at once?) Exceeding the max only slightly/briefly will get you significantly cooler water.
Tankless heaters do not put out cooler water when their capacity is exceeded. When the capacity of the heater is surpassed, which is really tough to do without a roman tub with their big gpm fillers(12gpm), the water coming out of the heater will still be coming out at the setpoint. The limit will be the gpm output of the heater. The temp is the same but the flow must be shared by the inuse fixtures.
Tank type heaters are commonly 50k btuh for a 50 gallon tank. Tankless can easily produce 4 times that much heated water. In order to get a tank type heater that is as efficient as a tankless at heating water, you will spend more than the cost of the tankless heater up front and that doesn't take standby losses into consideration.
The best tank type heaters still lose 1/2 degree per hour. For a 50 gallon tank, that is 200 btus. If you figure that times 24 hours and 30 days, you will arrive at a figure of 144,000 btus. That isn't bad at all but that is from a very expensive unit and not a large unit. A 100 gallon unit will lose 288,000 btus per month. Standard units can easily lose 10 times that amount. A circulating loop will lose far more than that as well.
On the issue of capacity, consider that most fixtures will use less that 100% hot water. A shower with a 2.2 gpm showerhead will use around 1.2 gpm of hot water and 1 gpm of cold. A Rinnai with 180/190 k btu output will supply 4.7 gpm at a 70 degree rise or 6 gpm at a 50 degree rise. That will service two showers, a dishwasher, a washing machine, and two lavatories at the same time without reduced flow.
There are several things to consider when deciding to go tankless or not, but capacity of the unit is rarely one of them. In the case of a roman tub filler, use two units or wait the six minutes that it takes to fill the tub.
Your biggest concern should be the 15k btu minimum demand for firing off the unit. In some instances, the unit will not fire for small hot water demands. This issue is not a factor if you use a hot water circulating loop but circulating loops will create a whole new set of issues.
Tankless water heaters are fine products that have cut my gas bill in half. I install them in every home I build only after discussing the pros and cons with my clients.
DanH
Boy, opinions vary all over the place. But so far decent high efficency water heaters the required size seem to be in that $600 to $700 range while tankless is around $1000
I'm not worried about the $300.00 I am far more concerned with monthy costs.. If the charts I've read so far are to be believed it will take less than 4 years to break even and that's assuming no price increases..
You at least have a chance of coming out ahead with a gas unit. None at all with electric tankless.I think the real balance is whether the space savings is important and outweights the limitations of the tankless unit.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
DanH,
Space is not a real consideration.. cost is. please read my logic in the previous post.. (I wasn't aware of electric tankless)
my plumber strongly recommends tankless.
woulda considered one when mine went out a coupla months ago ... but since we plan on being here no more than 2 more years ... and might be out in less than 6 months ... I went as cheap a buy in as I could.
as far as brands ... I'd have to check with him.
Which brings up my question ...
What does your most trusted plumbing advisor suggest?
my theory ... ask a pro then listen.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
JeffBuck,
few Plumbers buy my forklifts :) so I get a whole variety of opinions.. every single salesman who knows more than what the brocheres say believes his is the best and here's why,...
I've already got way too much time in finding out what I know so far, but since I intend to live here untill I turn into dust long time value is critically important to me..
I meant ... what's the guy doing the install suggest?
then ... realized you are probably doing that yourself too.
Jeff Buck Construction
Artistry In Carpentry
Pittsburgh Pa
I went with a pair of 40 gallon tanks in series, mainly because I had them. They were only a year old, from when the place had been apartments. The nice thing about tanks in series is you get constant temperature for a whole shower.
-- J.S.
There may be more in the archive about this than any other topic. Pour a tall drink, settle in for lots of reading, and do a search.
I calculated the payback on the additional cost based on actual cost and savings figures from my home when I tried one out years ago. The payback was considerably over a decade. Since the unit required repair twice then finally died after only a few years I decided that the risk was too high for the meager savings. If I had put the money in the bank I'd have made out much better. (The repair costs were not included in my payback calculations.)
The actual gas savings was in the neighborhood of $5 or $6 a month, in 1986.
WayneL5
I suspect your 1986 numbers are a bit out of date.. My summer gas bill which is only the water heater is about $30.00 a month. The forecasts I've been given would be less than 1/2 of that in three years I could save $540.00 while the tankless is only about $300.00 more than a high efficency tank type..
In addition no tank type uses outside air! they all consume inside air that is already heated.. plus the flue they use is open to the outside 24/7/365 drawing heated air outside. while the tankless will only send out it's own waste air while drawing in outside air..
A tank type is like leaving a window open even when it's 30 below as it sometimes gets around here. That plus using inside air means it creates an ever so slight vacumm, thus drawing cold outside air in to replace it..
My feelings are that not only will I save just on the cost of heating water, I'll save some also on the cost of running the furnace.
"In addition no tank type uses outside air!"WRONG.Direct vent and power direct vent units.
BillHartmann,
Please show me which direct vent and power vent units use outside air to provide combustion air.. I've spent several years asking local plumbers for just that sort of thing and to date nobody has found me one.. Maybe it's weather related thing. Maybe you can't draw combustion air if the outside temp is below say 20 below or some such number. I don't know.. I've checked with local building supply stores and plumbers and even checked with the gas company.
Power Vent, with outside combustion airhttp://www.hotwater.com/products/residential/rg-sv-pdv.htmlDirect Venthttp://www.hotwater.com/products/residential/rg-sv-dv.htmlThese are AO Smith, but most WH companies make them.
We have been running a Takagi TK1s for about 3 months. One-and-a-half thumbs up so far.
The flow sensor for this unit requires 5/8 GPM and our vanity sink, which seems like a trickle to me, will fire the unit no problem.
One can easily take a shower while the clothes are washing and the dishes are being washed too. No problem. I think we can get about 6 GPM with the typical temp of our well water and a 105-degree setpoint. I bought the remote control but have not connected it, so I don't know yet.
I put our unit in the attic. The tank we had was very inconveniently situated in the laundry room, taking up space that I now have available for a very large pantry cabinet. This saving of space is the single biggest thing I like about it.
Too early to tell whether fuel bills are lower, but I bet they are. I used to hate walking past the tank unit and hearing it burning propane when no one had run hot water in three hours. I'm sitting here in my office right now and there is no tank full of hot water being maintained... a feeling I like.
Our unit has a fan that propels the exhaust. This fan runs very briefly after the burner is done firing. If the unit were in a closet near living space you might hear this. We cannot hear it thru the ceiling.
There are two minor annoyances.
The first is typical of all tankless. When it senses flow, it takes a few seconds to fire up and then a few more to get up to setpoint. If you are turning the hot water on and off at the faucet, such as when rinsing dishes, you get a slug of cold water in the line every time you turn the faucet back on. In reality this water comes out in our kitchen as lukewarm because the insulated copper tubing heats the cold slug somewhat on the way to the faucet. If your unit was very close to the faucet and you were using PEX, you might not get this benefit.
The second is either a problem with my unit or maybe a characteristic of all Takagis. When I run a shower, it runs at the right temp for about 90 seconds, and then drops in temp by 3-5 degrees. I am used to this now so I just nudge the shower valve automatically to get back to the temp I want. A thermostatic shower valve would not have this problem, although it would reduce flow slightly when the incoming hot water cooled. I need to call Takagi about this one. This is entirely unrelated to other fixtures being used, time of day, well pump cycle, etc.
Bottom line, I'd get another one. I have to decide shortly whether to go with a small electric unit in the shop, or a small electric tank. I'm leaning towards a tankless since all it has to power is a low-flow shower and a vanity. I have done some reading on the large electric units and they don't produce a lot of flow in spite of requiring a nuke plant in the back yard for power.
edit: I say 1.5 thumbs up because the unit is relatively new, so I don't have any reliability data yet. It cost just under a grand, so it had better last a long time.
Edited 5/30/2006 10:06 pm by davidmeiland
Frenchy, Well I read a bunch of responses to your query and I have mine to throw in. Unfortunatly I have nothing good to say. (My momma always said if I had nothing good to say don't say anything) But here goes. I have four friends, in four separate houses in S. Fl who all have tankless. All of them have replaced thier units more than once. (One guy so many times he has a spare!) PNUTs posting,(#74388.5) is very accurate. I do not dispute a thing he said. To continue, and I apoligize for scaring you but one of the four is currently recovering from a house fire that resulted from a tankless. (It was properly wired by the way) There was no structural damage but there was a lot of damage. All of them like thier units, including the fire guy but I just can't get behind them. I have used all four at one time or the other in my travels down there and they really do produce tons of hot water. But I am not putting one in my current project. Sorry for my less than glowing review but you asked.
Knightdiamond,
Fire from a tankless, that would give me pause.. Except I do know of several fires as a result of tank type as well. I suspect that if we added up all the fires from tank type and all the fires from tankless and then correlated them as to percentage of tankless to tank type, there would be a tiny fraction higher incidents of fires in tankless due to mistakes in installation because seven generations of plumbers haven't learned the hard way the correct method to install tankless and what special needs a tankless has..
I'm not going to ignore your comments rather I can easily put the tankless in a spot where a fire can't damage the rest of the house (surrounded by cement block and well protected by fire rated sheetrock)
I am extremely interested in which brands failed your neighbors. I suspect it was Bosch, I really have heard many bad things about that brand, in fact Home Depot no longer handles it I suspect because of those failures!
Hi Frenchy,
Seems you have done your "DD". I can't recall what brand (s) they were. (Though I could find out). I am just a bit reluctant to post a "liability" type claim on this venue. (perhaps I am paranoid. Who knows.) But I figure you need to know. Are they all bad? I don't think so. Seems like I am the only one with this experience. But a man is spoda tell another man when he gots a booger on his nose and that was all I was doing. They certainly have some up side but I am not installing one myself. If that means anything. I wish you luck and if you really want to know the brand, its a simple phone call and I will do it for you. But the others on this subject seem to be pretty doggone up to speed. KD
Knightdiamond,
I have heard consistant negative reports of Bosch units with somewhat lukewarm opinions of the Rheems offerings.
Hi Frenchy,
Well, you are certainly get an earful. I hope you get enough info to make an informed decision. Like I said. I am not putting one in myself. (I happen to be building a energy efficient home and it doesn't really impact on me. Too much anyway.) I live in a rural community and we have fires enough for me to make that my single most important factor. I wish you luck and I don't think you are over thinking this! KD
I just had a Bosch installed into my home so I could direct vent it out the wall and eliminate the dedicated chimney for the old tank unit. The chimney was a thermal drain itself. To help defray the cost of the tank and installation you may want to check the federal government for current rebates http://wwww.tanklesswater.com/ed_energytaxcredit.asp
Mine qualified for a $300 tax credit.
As for the performance, it works great once you get used to the slight lag in hw response time.
I replaced a Bosch Aquastar tankless with a 50 gallon tank water heater. One of the reasons was that I wanted a gravity recirculation system and could not do so with a tankless. One of the reasons was that the response to transients was unacceptable to me. One of the reasons was the high pressure drop across the unit. I have 4 bathrooms in my house, I've had 3 in use simultaneously with the tank, though you could only use 2 at most with the tankless. I know they come bigger. Given the relatively high pressure drop though a tankless, any transients were freeze/scald events. I know that newer units have better controls but there will always be trouble with transients. They simply cannot react fast enough. I will never have a tankless water heater again, as my primary source of domestic hot water. At 1 gpm of hot water, and say a 50 gallon tank has 30 gallons of usable hot water, that gives a solid 30 minutes of shower time. These are conservative numbers, and I know the unit performs better that that. With the tankless I would never consider taking a shower if the washer or dishwasher was going. With the tank, never have to think twice about it. I did have a lot of guests over when the three showers were going at the same time, and the 7th person to take a shower said it "started to cool down a little". I can live with that limitation. Were I running a boarding house, I would have more capacity.
The tankless had a firing rate of 126000 btuh input, the tank is 45000, and takes about 45 minutes to heat 50 gallons of water from 55 degreesto 130 degrees. The tankless is a fairly effective heat source for my garage infloor heating system.
If you're having a recirculating system anyway, the presumed reduction in standby losses for a tankless becomes kind of pointless.Seems to me the ideal gas unit would be a super-insulated tank with a separate "tankless" burner unit, and a recirc pump to circulate cooler water from the tank into the burner. One could even make the tank electric for standby or off-peak use.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
I had an old 40 gallon tank water heater and bought the aquastar for the promise of eliminating standby losses and due to the need to replace a failing unit. At the time, my wife and I both worked 50 hrs a week plus, and were out of the house 12 hours a day. 10 to 15 minutes of use in the early am and maybe a load of laundry or dishes in the pm. We realized very good savings in the elimination of standby losses over the old tank. My plan was to install 2 tankless units, one handle the NE end of the house and one to handle the SE end of the house. After a year of use with the first one, the shortcomings of this type of unit were appearant, most noticable/problematic were the transients and high dp. Steady state performance was exception I must admit. But, in the far reaches of the castle/money pit, the wait for hw was too long. During renovations I allowed for the recirc, having made the decision that my preference was to replace the tankless with a good, well insulted tank, of large enough capacity to reasonble handle a 4BR, 4 bath home.
I could devise no practical way of eliminating the wait with the tankless, at least none that I was willing to implement.
Ideal, to me would be a small but potent indirect (with enough boiler capacity a 30 gal indirect has similar 1st hour capacity as 100 gal "self-fired" commercial units) fired via a condensing modulating boiler, with a well engineered recirculation system for convenience. In reality such a setup is almost as you describe, because during single fixture demand, an indirect coupled with a decent sized boiler (assuming the capacity is required for design basis heating load) is an instanteuos water heater with a storage tank.
Another option instead of the recirc loop is multiple small electric tanks, fed with hot water from the centeral unit.With a central tankless unit this would also handle the warmup delay problem.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
"multiple small electric tanks..." Sounds elegantly simple!
The only problem is that most small electrics are poor quality and don't have large inlet/outlet ports for full flow (though maybe there are exceptions). What you really want is something of the quality of a Marathon unit, or at least the better-quality State.
(Well, actually Marathon does make a 15 gallon unit (a hair on the large size for this duty), and they claim it has 3/4" ports. Probably expensive, though.)
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Edited 6/1/2006 2:45 pm by DanH
Tankless has a big advantage for things like a church building that's really only used on weekends. No sense keeping big tanks hot all week long and not in use. The bigger the family, the more constant the HW demand, and the less advantage to tanklessness.
-- J.S.
JohnSprung,
We all shower in the morning , starting at about 6 untill about 7 there is almost always a shower going.. the dish washer comes on shortly after we leave for work and then untill we return in the evening when hot water is briefly required for the evening meal.
Total time required to run the hot water less than an hour and a half per 24
My Aquastar125 has worked very well for three years. I was able to install it in a pantry in a central location that saved money on both chimney and plumbing, and kept drilling big holes in stuff to a minimum. I have a 6' Kohler soaker tub to feed, so even if it cost more... I use 450 gals of propane/year for both heat and water. I would do it again, but probably use a Baxi and do the whole house with RFH, too.
I found a lo-flow shower head would not trigger the Aquastar, though. Brrrr!
>>>>Stop me before I over think this!<<<<
Too late.
The destination is not the point. The completion is not the point. Enjoy today. If you can't enjoy today, then what is the point ?
You don't say how close your tankless would be to the gas meter and how much flue pipe you need as well as where you have to route it. These things are important because:
1. Tankless capable of keeping up with two showers use 175,000 BTU/H or more, which limits you to no more than 20 feet of 3/4" pipe run. I installed one for a family whose meter was 65 feet away - had to run 20 feet of 2", 40 feet of 1 1/4" and 5 feet of 3/4" to get enough gas volume - so repiping cost them $700.
2. Big volume tankless requires forced draft flues, which means expensive stainless double-walled pipe with special sealed fittings - just 6 feet with two 90-bends - cost $300 plus installation labor.
3. If the flue must pass up through a wall to the roof, you cannot use high capacity devices because they require a chase with several inches clearance from the flue pipe within.
Gas savings can be illusory as well. This family went from 40% efficient old 30g tank heater that was insufficient for their needs, to 80% efficiency and inexhaustible supply of hot water, and therein lay the problem - two teen aged sons no longer ran out of hot water so they took longer showers. My customer told me that his gas bill actually went up as a result.
Brucet
"1. Tankless capable of keeping up with two showers use 175,000 BTU/H or more, which limits you to no more than 20 feet of 3/4" pipe run. I installed one for a family whose meter was 65 feet away - had to run 20 feet of 2", 40 feet of 1 1/4" and 5 feet of 3/4" to get enough gas volume - so repiping cost them $700."
Assuming 1100 BTU/CF you can run more than 40 feet of 3/4" line. For your 65 foot run you could have used all 1", unless you had branches to other appliances, in which case maybe the 2" was required.
"2. Big volume tankless requires forced draft flues, which means expensive stainless double-walled pipe with special sealed fittings - just 6 feet with two 90-bends - cost $300 plus installation labor."
Single wall category III is appropriate for most of the installs I have seen and done. According to the Ira Wood website, (2) Protech 4" x 36" lengths plus (2) 90 elbows will run you $172. Have you had to use the double wall?
"3. If the flue must pass up through a wall to the roof, you cannot use high capacity devices because they require a chase with several inches clearance from the flue pipe within."
The clearances are not much different than for B vent... maybe as much as 2" I think, but not more.
I'm not saying that gas line sizing is not an issue, or that the venting materials aren't expensive, but it is not that hard to get a tankless into most places that a typical gas heater would go. Certainly anyone thinking about installing a tankless should consider carefully where it will go.
"Assuming 1100 BTU/CF you can run more than 40 feet of 3/4" line. For your 65 foot run you could have used all 1", unless you had branches to other appliances, in which case maybe the 2" was required."Don't forget that each elbow counts as 5 feet for purposes of pipe sizing calcs. To get around obstacles and for esthetic reasons, one rarely can take the straightest route. "Single wall category III is appropriate for most of the installs I have seen and done. According to the Ira Wood website, (2) Protech 4" x 36" lengths plus (2) 90 elbows will run you $172. Have you had to use the double wall?"Instructions with the Bosch unit that I installed required specifically the 3" pressure-rated type."The clearances are not much different than for B vent... maybe as much as 2" I think, but not more."I remembered clearances in closed runs being greater than 2", but be that as it may, you still can't use that existing rectangular flue inside a stud bay.BruceT
Are all these tankless units running at 80% efficiency in the field or just in the test labs?
For Frenchy: Did you get the electric and gas rates or did I miss a post?
experianced,
Sorry I missed posting those. Wife's asleep so I'll post them tomorrow..
BruceT999
You brought up something that I hadn't thought of.. The exhaust could be right thru a 12 inch block wall Unit mounted on one side with outside wall on the other.. Nearest shower (master) would be approximately 12 feet from unit, farthest would be 24 feet. (3 bathrooms with showers are all in a central core..) Kitchen would remain the longest with nearly 40 feet to kitchen sink..
Through-wall venting is possible so long as there are not any plants, pets or people likely to be close to the vent outlet. I think that under eaves may also be a no-no because of the very high temperatures of the exhaust gas stream. BruceT
BruceT999
Thru the wall venting is no big deal.. exhaust is sent sideways instead of up for only a marginal benefit.. Thru the wall fresh air intake however is a major benefit.. instead of preheated (or conditioned air) being used to support the combustion, outside, (cold or unconditioned) air is used.. If you burn inside air something has to replace it since mother nature hates a vacuum. That low pressure inside the house caused by the fire in the water heater sucks in cold outside air. however when the combustion area is feed thru outside vents no inside air is lost..
My much bigger furnace vents right into a bunch of outside bushes etc.. The only problem is when there is a lot of condensation and Giant frozen icicles cover the plants in the winter, damage can result from broken branches etc.. as far as intake of carbon monoxide into an attic etc. from the outside vent, that's pretty tough.. assume that we are only talking about a ramblerwhile the warm air rises it does have almost infinate amount of space to disapate even in the 8 to ten feet between the furnace vent and the eves.. even in absolutely still air there are still little zephers of wind blowing around to disapate it.. It was extremely closely tested in the preprotype stage. (developed here in Minnesota)
Edited 6/4/2006 11:25 am ET by frenchy
Not sure if this is available on tankless waterheaters, but my gas fireplace uses a dual-wall pipe. Exhaust up the middle, combustion air intake in the outer passage. The exhaust preheats the intake; the outside air cools the exhaust. Win-win.
wrudiger,
It's fairly common, and Bill Hartmann reports that tank type water heaters are available with that sort of construction. While I haven't found any here in Minnesota that would solve my problems regarding using gas water heaters as the heat source for my In floor radiant heat system..
Every tankless water heater I've seen has that arrangement..
My much bigger furnace vents right into a bunch of outside bushes etc
What happens if your furnace happens to malfunction and the flue gasses get very hot.......a fire in the bushes.....then up the house. Up here, side wall venters must be at least 12" above plants, bushes due potential fire harard.
experianced,
Have you ever felt the exhaust from one of those high efficency furnaces? It's only warm compared to the air outside.. your exhaust pipe is a hundred times warmer and it passes directly under (or next to) your gas tank.
My high efficency furnace is plumbed with PVC pipe. yah! regular old plastic pipe like they use for plumbing!
If there were any danger of a fire, that would be the first thing to melt and yet it's code approved! Not only that but it's installed by the gas company that way and inspected!
Now my vents happen to be about a couple of feet away from the bushes, just well hidden behind them. The only time any of those big Ice cycles I spoke of form is on super cold days (minus 20 or colder..) as soon as the temp warms up to about zero they melt and they aren't an issue..
Didn't know you had a high efficiency condensing unit!!!
frenchy,
I came across an electric tankless:
http://www.seisco.com
The propoganda makes it seem like a good product.
Pete