Alright, i’m pretty sure i know the pros and cons of tankfull vs. tankless… however here’s my issue:
I anticipated this problem. Some of you may know that my shower is actually a small car wash. I like my showers warm and i get a solid 15-20min shower with no problems…the wife likes the shower HOTT…and gets about 5min before the water goes cold.
My Hot water tank is fairly new, 2yo i belive and is 50gal. I have the temperature turn all the way up as it is. Basically my shower can drain the 50gal tank in about 5 mins.
Since the existing tank is fairly efficient and new i was considering to keep the tank and maybe throw the tankless in series with the current plumbing. My thought process with this is that I can adjust the tank to run/operate at a lower water temperature. When the water from the tank reaches the tankless…there is a somewhat consistant water temperature throughout the year allowing the tankless to operate at elevated temperatures without reducing the flow rate (i.e. having an inlet water temperature of 85°F vs. 50°F) reducing the wait time for water to heat up. It’s only about a 15ft run from tank to shower.
On the other hand…after 50gal passes through the tankless…the water will again be colder and the tankless will need to work harder to maintain the same temperature.
What’s the fixed variable on a tankless? the outlet water temperature or the BTU’s? If it’s a fixed temperature…the BTU’s will adjust accordingly to get the right temperature out. If the BTU’s are fixed…then the outlet water will get colder as the inlet water temps get colder.
I’m thinking in this case the PRO offsets the CON equally…making it a project not worth doing… but i may be missing something here.
I think you’d be better off getting a larger traditional hot water heater.
The problem with tankless is they are designed around the US spec low flow fixtures. If you’re draining a 50 gallon in 5 minutes you’re obviously not running low flow stuff. You bandaid of pre-heating 50 gallons worth only solves the problem tankless heaters have with our super-cooled winter supply water but does nothing to address the fact that after 5 minutes that incoming water will be back to street temps. Even before it’s drained I have my doubts that a tankless could keep up with your flow rate and once the 50 is empty and the tankless is trying to heat 50 degree water you’re totally boned.
Do a search, we discussed this at length when Fry was thinking about getting one.
I know my uncles house has a sepperate tankless for each bathroom, so one for just the shower would be fine. I would not however connect a warm line to it. I would think it would be REALLY hot once it comes out of the tankless and create some problems, and I don’t think there is a great efficiency there. I would turn the reg one down a bit and install the tankless for the carwash.
^ the other option…would be to run the tankless INTO the tank…so the tank regulates the temperature which all of a sudden makes more sense to me.
also…with smaller showers i can see this working, but according to the non-percise calculations… i’m flowing 10GPM of hot water alone (plus whatever for the cold side). So if i use a stand alone tankless for the shower…i need a 10GPM heater just to feed the shower which is a pretty big heater for elevated temperatures (Probably like 15GPM at lower temperatures)
---------- Post added at 03:14 PM ---------- Previous post was at 03:05 PM ----------
I had read that…and know that some have used the smaller 10gal tanks, but that really only limits the initial blast of cold water if you were using hot water…turned it off for whatever reason…then resumed using hot water again. Once you get the flow going for a period of time, you’re just feeding it right through the small tank without giving it much of a chance to heat…at that point, it’s pretty much the tankless doing all of the work.
What about turning the 50 gallon up and installing a thermostatic regulator valve to mix cold water in with the super hot so the tank can catch up faster and it won’t scald you.
the tankless heaters are only good for low volume usage, which is why they are so popular in the southern states in patiohomes and the like. The “science” end of things is that it takes LESS energy to RETAIN a temperature than it does to CREATE a temperature.
A co-worker put a tankless in about 4 yrs ago and he loves it because “he never runs out of hot water”. he says his gas bill did not change much, and the only “con” he has found is pressure at his kitchen sink is low, which is the farthest point from the source. In my opinion a tankless isnt really practical in our area, I have a really tough time recommending one no matter what. If it was me, I would either get a larger traditional tank, or run twin tanks. I can’t believe you are capable of using 5ogal in 5 mins! haha
the only other thing is you could maybe put in a pressure regulator and slightly lower the pressure going to the shower, so that while the water is equally as hot you are using LESS G.P.M.
I would do a pressure regulator and larger traditional tank. I have no experience running a supply>tankless>traditional-tank setup so I cannot comment on the possibility. I haven’t worked at an architecture firm in 2yrs.
Yes but if you now install the valve instead of having a shower of hot water come out on a small setting on the knob in the shower you can mix cold water in at the tank and it will prolong the reserve for a longer shower. I have 2 showers in a multiple unit running on one 40 gallon tank. We have yet to run out of hot water. I realize that you are running delta sonic in your bathroom and all but the valve was 100 at Irr supply rather than 1500 for a tankless hot water system like we were going to go with.
Fiance takes 15 minute hot showers… to the point that I cannot understand how she isn’t covered in burns when she gets out.
for all the shower fixtures…i have a thermal control and diverter valve which allow for flow adjustment. I mean, i have the ability to control the volume of water and extend the shower time to an hour if i wanted…but what the hell…the water pressure is half the fun.
Using the tank in serial is just not really a good option. You will run into the issue where there is a lag time once the temperature changes with the tankless.
Tankless water tanks have different flow rates, their max flow rates are a good gauge on what you should be looking for. However, the flow rate you want to using should be in the middle to low if you want extremely hot water. During the summer it is not an issue, but the tap water is colder here in the winter and if you are trying to get really hot water (scalding) at the highest flow rate you won’t be able to get it.
We have a 6 or 7 gpm bosch tankless heater in our house after our traditional water tank failed. (tax credit, rebates, etc. made a regular and this about the same price) I have the temp set at about 150 on the unit and in the shower with a 2gpm flow head it works great.
Here are my major dislikes with the system:
The long draw length to the bathroom causes a decent length of time before hot water gets up to you.
If you take a shower and someone else gets in to take a shower, you will have warm water and then because the tankless shut down in between showers you will get a short spurt of cooler water before resuming normal. Really fun in the winter when you think its warm water again and then turns cooler right about the beginning of washing your hair.
If you just want a little hot water like washing your hands or like to turn the sink with hot water on and off a lot (doing dishes or kitchen work) it feels in efficient, because the heater keeps kicking on and off and you have to wait longer for the water to stay warm.
If I was in the situation as you this is what I would do.
Find a good 8-9 gpm unit (double check that your shower flow rates are gonna be no higher then like 6 or so with that) and hook that directly to your shower unit.
Use your Tank heater for the rest of the houses hot water needs and you will basically remove all the draw backs of having a tankless for normal hot water duty.
Also I to answer some of your questions that you had, tankless try to maintain an exit temperature and will adjust the btu’s up to a certain point. Obviously if you are maxing out the btus on the unit and it can’t reach the exit temp because the intake temp is so low then the unit does not have enough power.
you can see the run here. The shower is where that little step/bench stool is and the tank is to the right.
maybe i’ve got the wrong idea…but isn’t it basically mixing cold water with the hot water? Meaning warm water comes out instead of “hot”?If so…that just means that the wife will turn the knob hotter and the end result will be the same?
Our water pressure is exactly the same as it was before and after the tankless.
Our gas bill usage is now half of what it was with a traditional tank. (Though the traditional was an older unit 10years or so newer ones are better now)
Tankless liking low flow situations completely depends on the unit. If you have a 10gpm unit, it will have issues heating a .5gpm, because the burners can’t kick on without it overheating the water due to how slow it is moving. However if you have a 2gpm unit it can handle those lower volumes without a problem. 6gpm loves 2gpm shower heads.
The tankless will make the wifey happy with you, because she can spend all day in whatever temperature shower she wants.
Oh and easiest thing to do is time how fast the shower takes to fill up a gallon pail when running the shower. That will tell you exactly the gpm with some math, test that with your shower method and your wife’s method to see which is higher (most likely the wife).
what about what i mentioned in Post #5? If i run the tankless into the tank… When the hot water is in demand, it will be feeding the hot water into the tank where the water is already hot. techincally the tank will only turn on if the water gets below a certain temp but then you would be taking advantage of the “endless hot water” from the tankless until a certain point where the draw from the tank has emptied the existing hot water and whatever the tankless can provide without reducing the flow. The hot water may not be infinite in this case…but i may get 120gal of consistant hot water versus 50-60gal from the tank alone. (pulled those #'s out of my ass)
Yes but once the thing is on the flow rates are the same correct? I mean when I turn my shower on I get the same flow rate whether or not it’s on cold, hot or any mix there in. If you turn the tank up and install the valve the tank will start heating the incoming water when the reserve is being drawn the out put from the tank will be fucking hot. However the mixing valve will add cool water so you don’t scald yourself. All this is doing is prolonging the reserve. Seems to work really well at my house. 2 apartments using hot water. 2400sqft
yeah the thermostatic valve output volume is constant (i also have a flow valve that allows me to restrict volume if i desire).
trying to reason this out… Typically hot water tanks heat when the temperature reaches a certain low temperature…so there might be a few minute lag? This causes a drop in temperature without the tanks ability to keep up…slowly draining the tank of hot water. Correct? While this valve will heat the water once there’s a draw without waiting for the temperature to drop?
It sounds like you’re trying to put a band-aid on the problem. I have one of those hot tub/steam shower setups with multiple shower heads. As a result, I had to get a tankless just so I’d be able to fill the hot tub (90 gals) all the way with hot water. I got a tankless that was several sizes larger than what was commonly recommended for a normal house. I did this because the flow rate of my shower is much higher than a standard shower head (my unit has two 3/4" water lines feeding it) and, I didn’t want the shower to suddenly become ice cold if someone turns on another faucet or the washing machine, etc. Mine keeps up just fine with the shower, the kitchen sink, and the washing machine all running at once. Most tankless units have variable gas valves so you are only using as much fuel as needed to keep the outlet temp of the water consistent at whatever temp you have it set at. I’d ditch your current tank on CL and spring for the tankless.
That might possibly work, but I still think a tankless would be able to provide your shower enough flow/temp to not have to worry about working the tank into the equation for the shower.
Also, unless you do something with the valves like carnut is talking about, the output from the tank is going to vary in temperature a lot more then it will from a tankless.
---------- Post added at 04:01 PM ---------- Previous post was at 03:59 PM ----------
What gpm is your tankless unit? Links?
I still think using the tankless for his shower and the tank for everything else would give him the best of both worlds.
If you truly are at 10 gallons per minute for your shower that is a lot of water to heat. Rather than go the Traditonal Tank to Tankless the more effecient way would be to disconnect the Traditional tank and run the cold right to the tankless just for the shower. Smaller tankless system are used as “point of use” systems but cannot produce 10 GPM. You will need a “House” unit and isolate it to one fixture, the shower.
Assuming your wife is like my fiance, short of the humidity peeling the paint off the walls, the water needs to be near 115-120°F. Average ground water temperature is between 65-70°F. Meaning you need a 50°F rise at 10 GPM.
You have two options:
Find a drop in heater that meets 50°F rise at 10 GPM.
Run two (or more) smaller units in parrallel giving you a 50°F rise at 5 GPM
I have looked into tankless systems. I will get one once my current one starts to go.
