“Special” tankless water heater?
My wife and I replaced our 40 gallon tank water heater last June with a newer 40 gallon model. For the most part, this has worked fine; however, with the colder weather and the colder water coming into our home, I have been unable to fill my tub at a temperature that is to my liking. It is not like we have a huge tub, we don’t. I figure that the new heater does not have a recovery rate capable of heating the water at its current temperature as it is refilling the tank. I have tried everything including turning the new water heater all the way up an hour or two before I take my weekly hot bath, however, nothing seems to work. The cold water runs out, and I simply cannot get the bath hot enough for me.
I know that if I had bought a 60 gallon tank, I would almost certainly be OK. However, that is no longer an option for me.
Here is what I would like to do. I would like to buy a tankless, and install that into the feed line for the tank heater. This way, I figure that the tankless’ more efficient burner will be the main source of heating energy, and the tank will store the pre-heated water, and possibly add heat to the water if it is not quite up to temperature and also when the stored water in the tank cools down. (We got a model that had a fair layer of foam insulation, and I added an insulation blanket to the outside, too.)
Now my question. Do I need to get a tankless model that is designed to work in this scenario? In other words, do I need to look for a model that is specifically designed to feed a “tanked” water heater, or will any tankless model work for my application of “preheating” water that is going to be stored in a tank?
If I need to have a model that is designed to feed a tank, would you please recommend manufacturers?
Thanks.
All the best,
Matthew
Replies
First of all let me state that I hate "tanked" water heaters. That said, one thing that I have noticed with some of the smaller elec tankless (as well as some standard units) is that faucets and shower heads have flow restrictors built in and the tub fill does not. Try slowing down the rate of flow to the tub and see if you can get it hot enough. As far as a tanklees in tandum with a stroage tank.. .maybe plumber will answer. You would at least need a second pressure tank and I would think a second relief valve
Others will help with your questions but I have a few thoughts. Since you replaced your old 40 gal unit I can assume you have an older home.
Some things that effect tempatures, like old cast iron tubs and tubs over a crawl spaces. If this is the case consider accessing under the tub with some sort of spray foam to insulate the tub. Look to see if there is a crawl space vent open near this bathroom, with a few exceptions they should be closed in winter.
If it's a cast iron tub on slab consider replacing the tub. American Standard had a unit with a cast iron finish look called Americast. There are many other units that look as nice without displacing so much heat.
There ought to be more than enough hot water from a tank that size. The bathtub wouldn't even hold 40 gallons, so you should be able to empty the entire water heater into the tub and be plenty hot.
When filling the tub do you start running the water "too hot"? The water cools down as you draw more out of the heater, so you have to start filling the tub with water that is too hot for a bath. As the tub fills, the water cools to a comfortable level.
Check that the water heater was installed correctly. If the hot and cold connections were swapped it could cause your problem.
Actually, have the tankless installed between the 40 gallon unit and the tub/rest of the house. This way the tankless only comes on when the water gets too cool. Running heaters in tandem works fine. It will usually solve your lack of hot enough water.
I'm a little suspicious of your new water heater. I would think a model for model replacement would deliver the same performance. Did you buy the cheapest one you could find, or did someone else make the buying decision (plumber)?
Tu stultus es
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Thanks to all who replied.Changing the tub is not an option - even getting the wife to go with letting me put in a tankless might be a feat in and of itself. ;) However, if I buy the right model, I might be able to convince her based on the $300 tax credit and not having me complain each week that I cannot get the tub hot enough.The water heater is hooked up correctly. I was able to correctly identify the "in" port and the "out" port when I hooked it up. ;)The new model's recovery rate is somewhat less than the recovery rate of the one that we replaced, however, I do not know how much less it is. So, the assumption is that it does not have the thermal output of the one that we replaced. Its probably the price I've paid for being a "do-it-yourself-er."Basically, it met the wife's requirements of having a pilot. It it has a standard mechanical thermostat. It was a box store buy with a 12-year warranty at about $480. Cheaper models have 6 or 9 year warranties.We did not buy the cheapest water heater out there. That said, this model has a tall, thin tank. IMHO, this is not the way to do things. It would seem to me that in a tall thin tank, if the incoming water were not injected in the right place that turbulence could lead to excessive mixing with hot water and significantly decrease efficiency. That might be hot air on my part as I have not done a fluid dynamics study. ;)Also, our tub is fairly deep. Even with the old water heater (also a 40 gal), it was impossible to fill the tub even without anyone in it and still have hot water left over. My guess is that it easily holds 40 gallons. Even with the old water heater, I was able to get in the tub and get the water to a temperature of my liking without running out of hot water. The old water heater had a larger diameter and was shorter than the new one. So, the long story short is that I cannot get my weekly hot bath hot enough for me with the new water heater.I am also reasonably sure that it is the original tub from the 1950's. It is not a really really old cast iron tub, but is almost certainly cast iron. It is also not in an area where it is exposed to excessive drafts. The tub is directly over our kitchen and is separated from outside walls by a storage compartment and a closet.I have also tried throttling the hot water flow, it does not work. Also, running hot water in first and reducing the temperature to a comfortable level by adding cold water would work, however, I will not be able to get the depth of water to my liking. There is simply not enough hot water in the tank to get the tub to both a temperature and depth that I prefer. If I get in and run in hot water mixed with cold and attempt to bring the water up to temperature when I am in the tub, the hot water runs out. It is not a matter of my getting in, putting in too much cold water then not being able to get it hot enough because of too much water in the tub. The hot water runs out, that is, the hot water faucet gives me cold water.Two things come to mind. 1. The thermostat is defective - and that does not seem to be the case. There is plenty of very, very hot water for small tasks like washing dishes. 2. The unit simply does not have enough storage and/or enough of a recovery rate (i.e., heat output per unit time) to satisfy my "hot bath" wishes.Thus my thoughts of using a tankless as an assist.So, on using a tankless after the tank, would it not be more efficient in the mostly low demand situations that occur in our two person home to have the tankless on the feed side of the tank? Worst case, the temperature rise would still be much higher than having cold water coming into the tank, and I figure that it would give me enough hot water to give me my hot bath. If the tankless were on the output side of the tank, then it would not turn on until the tank is basically empty, or the water coming from the tank were below the turn on temperature of the tankless. I suppose that the gain in efficiency in this case is a matter of preference. I can see that having "pre-heated" water going to the tankless might be a better approach, and might be better at compensating for cold winter supply water.Thanks again to all who replied.Best Regards,
Matthew
Also, our tub is fairly deep. Even with the old water heater (also a 40 gal), it was impossible to fill the tub even without anyone in it and still have hot water left over. My guess is that it easily holds 40 gallons. Even with the old water heater, I was able to get in the tub and get the water to a temperature of my liking without running out of hot water. The old water heater had a larger diameter and was shorter than the new one. So, the long story short is that I cannot get my weekly hot bath hot enough for me with the new water heater.
I'm confused; it was impossible w/ the old one to fill the tub up, yet you also say you were able to do it. Typo?
I agree ... your tub will probably easily hold the 40 gallons.
Why did your wife 'require' a pilot light? Seems so definate w/ no apparent reason. In hind sight you should have gotten a power vent/ignition higher efficiency w/ a recovery rate better than what you had (or at least as good).
Thanks for your reply.No, no typo. If the tub was empty the old WH would run out of water. I stated that only to emphasize the point that the tub likely holds more than 40 gal. If I was in it, thus requiring less water to fill the tub, I could fill the tub to my liking.And you know what they say about hindsight. ;)The wife wanted the pilot so that we would have hot water in the event of a power outage. Also, she was in a hurry to replace the old water heater since it was leaking. I felt it could have gone longer and we could have waited for a tankless, but I have not been one to argue, yet. ;)We researched the Aquastar that uses water flow to provide a spark to light the burner. (My guess is that it either drives a piezo or a small generator to generate the spark.) Users of that particular model have said it lights unreliably. That was a problem that neither of us wanted to deal with. Also, I found a Rinnai tankless that had battery backup, but the wife did not want to wait as the only place that I could get one as a consumer was over the net.
wiyosaya, many seem to like the new "tankless" water heaters, but let me present an alternative view ... we hate them. We had both. Biggest complaint about tankless is the inability to get low flows of hot water. Couldn't shave, wash my hands, or wash veggies ... anything that required a trickle of warm water. The tankless cut out around 1 gpm. Drove us crazy. The cook was always mad! ugh! I would shave with the hot water running in the tub. My wife was not so lucky in the kitchen. I monitored energy usage (nat gas) for two years before I replaced it. Those advertized savings of 50% only apply to vacation homes where the guy never lowered the HWH temp when he left. I found NO savings here either. Maybe cuz we wasted so much energy running more hot water than we needed in order to prevent low flow shut down. It was a happy day in our house when that old tankless got removed.The jerk who put mine in (came with the house) vented the heater's 7" diam flue into a 2.5"x6" tile chimney. Little problem, huh? The home inspector never caught it. I wonder how many others get missed. And that's another chief complaint. It ain't easy to upsize chimney flues on old houses.
Finally. Someone reiterates what I've been preaching about when selecting tankless models.
Plumbers will sell you on high flow rates or the number of potential showers to be taken at the same time. Rinnai seems to do some special advertising support of many plumbing companies and their low rates are some of the worst.
Frankly, the number of instances where the high rate comes into play vs the number of low flow instances are grossly out of relationship. High flow rate issues can be dealt with by behavior/education. Low flow issues cannot.
I favor the Tagachi T-K3. It'll run a couple of showers at once, or after starting at 0.5 gpm, it'll go down to 0.4 before cutting out. Just about right for shaving or washing dishes.
Sounds like your install was a DIY.
PeteShlager, the guy who owned the house before me ran a section 8 housing enterprise (think ghetto) and used his own "people." Some of his work was worse than DIY, it was more like DIE. I wanted so badly to "walk" at closing, but my wife loved the house, so we bought it. 8(Thanks for the comments about the Tagachi tankless. They may have solved the problem which was our chief complaint. I would still have needed another flue, correctly sized. With the transition to high-efficiency furnaces, and their PVC side exit pipes, maybe plumbers are now using old vacated furnace flues for tankless heaters.
Have you compared the BTU ratings of the new and old heaters?
Mike
Fill tube might have come off or broke and your incoming cold water is staying on top where your hot water outlet is.
That sounds like the right answer. If the tank heats 40 gal to hot temp, even if it is slower getting there than the old one, there will be plenty of hot water to fill the tub.If the fill tube is installed correctly it should bring cold water in at the bottom, forcing hot water out the top without significant change in temp. Slowing the flow rate to the tub would actually lower water temp due to its spending more time in the pipes along the way.This sounds like a warranty problem to me.BruceT
Thanks for the posts on the fill tube.The fill tube sounds like a possible cause. Would you happen to have any suggestions as to how to test this to see if this is the case?We do get hot water for some time before it runs out.Thanks again.
Release your pressure relief valve and shut off your water supply. I always like to drain a little hot water as well, either from the drain or run it in the house. Disconnect your cold water line. From here, I'm unsure, unless I'm actually doing it. You might be able to see the top of the fill tube, with the lip hanging over the edge of the inlet hole going into your heater. If you don't, you have to take off the fitting where your water supply line hooks to the heater. When you lift it up, your fill tube should be attached and should be almost as long as your heater is tall. If it is broken further up, or came off and floating around in your tank, get a new one. Less than $10 if I remember correctly. It's just a platic pipe that takes your incoming water down to the bottom of the tank closer to the gas flame. You might also want to flush out your tank to get out any little pieces at the bottom.
Tracy
Get yourself a 5 gallon bucket. Fill it with hot water as many times as you can until you get cold water. You should get about 8 buckets full and it should fairly abruptly turn cold if you did it quickly so that they tank doesn't have much time to try to recover. If you get significantly less than 8 buckets full, I would suspect the fill tube is missing or broken off short so the cold water is mixing with the hot rather than being placed on the bottom of the tank.You are probably best of to do this test right after the tank has shut off at the end of a heating cycle so you do not have an unknown amount of cold water on the bottom from small water usages which are not enough to trigger the burner. Make sure that your wife isn't doing the dishes or laundry will you run the test.
Many, many thanks to all who have replied. Lots of very good suggestions here and great troubleshooting advice.I'll verify whether it is a fill tube problem before deciding what to do.I like the idea of using a thermostatic valve inline somewhere other than in the bath itself. Doh! I should have thought of that. :)Thanks again.Best Regards,
Matthew
I tend to agree, too. Definately something to check.
What is the temperature setting on the new water heater?
Did the plumber install some kind of manual mixing valve (i.e. blends in some cold water with the hot water to the fixtures) that was NOT there with the older tank?
The manual mixing valve lets in a fixed amount of cold water blended with the hot water. When the temp of the pure hot water drops some with high volume usage, that manual cold blending is too much cold water. A thermostatic mixing valve would regulate the final hot water temperature to the fixtures.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
There is no mixing valve. I was the plumber.Also, I have discussed a temperature controlled valve with her which I think is a great idea. She does not want to rip up the wall in the bathroom. Believe it or not, installing a thermostatic valve in the bath would be a bigger job than putting a tankless in the line in the basement.
Got a thermometer?
I would check the temp of the output & time it on how long it can run before it drops below your desired tub temp.
If you want to play engineer or have a teen kid here's a good math problem for them/you.
M = mixed tempH = water heater outputC = cold temp
M minus C over H minus C = % of hot water required.
Example
Desired temp of 105 degrees, hot water output of 120 degrees, cold inlet temp of 55 degrees.
Requires about 76% of hot water mixture, 7.6 gallons of hot water for every ten gallons used.
You do not *have* to rip up the bath wall to have thermo mixing. The mixing valve could be done at the water heater close piping.
I would raise the standby temp of the water heater. A low stand by temp could cause nasty microbes to grow in the tank.
Raise the temp to 140*F. If it is just adults who use the hot water, regulate the faucet temp by hand w/control at point-of-use, or add a thermo mixing valve somewhere if children use the hot water.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Might be cheaper to replace it with a new larger tank style than to install a tankless.
What size tub do you have? A 40 gallon heater should be sufficient to fill a conventional sized tub. If it's not working there's probably something wrong with the heater. One simple possibility is that the hot and cold are reversed.
My wife and I have a two person whirlpool type tub and a standard 40 gallon water heater. To get it filled we turn only the hot water on (Roman two handle faucet, so less than full blast). By the time the tub is nearing full, the hot water has turned into warm water. Then we mix with cold to get the right temp.