# Tankless Hot Water issue **URL:** \ **Category:** Factual Questions\ **Created:** [December 10, 2015, 3:57am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057 "2015-12-10T03:57:37Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [December 10, 2015, 3:57am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/1 "2015-12-10T03:57:37Z")
I installed a 10 LPM whole house Natural gas (80,000 btu) water heater in my wife’s sisters home. I am not happy with the flow rate of this system as in to flow 140 degree water the unit has to be throttle the water throughput to under 2LPM flow. My next idea is to install another unit just like the first one and run them in series to get hot water sufficient to take a shower?? Or is there another way of improving the system??? ---
**Author:** ![snfaulkner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snfaulkner/32/433_2.png) [@snfaulkner](https://boards.straightdope.com/u/snfaulkner)\ **Post date:** [December 10, 2015, 4:10am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/2 "2015-12-10T04:10:19Z")
> [@Gbro](#): > > I installed a 10 LPM whole house Natural gas (80,000 btu) water heater in my wife’s sisters home. I am not happy with the flow rate of this system as in to flow 140 degree water the unit has to be throttle the water throughput to under 2LPM flow. > > My next idea is to install another unit just like the first one and run them in series to get hot water sufficient to take a shower?? > Or is there another way of improving the system??? Are we…are we still talking about fireplace matches? I guess you could light them and…uh…heat…water…with them?:dubious: ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [December 10, 2015, 10:12am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/3 "2015-12-10T10:12:07Z")
**Moderator Note** The above two posts have been separated out from their original thread as it appears that this was intended to be a new thread that was accidentally posted to another thread instead. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 10, 2015, 10:31am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/4 "2015-12-10T10:31:38Z")
140 degrees is a pretty hot shower. The “normal” shower temp is between 100 and 120. Have you actually measured the temperature of the water? > [@](#): > > Anything below about 80 degrees is down right cold. So, our lower limit is 80 degrees. The upper limit is likely to be about 120 degrees. Anything above that is likely to scald you. > **[Homes and Houses: What is the average shower water temperature?](https://www.quora.com/Homes-and-Houses/Homes-and-Houses-What-is-the-average-shower-water-temperature)** > > Answer (1 of 47): A question like this is certain to attract a wide range of subjective responses. Aside from a few anecdotes about recommendations from doctors and dermatologists, most of the existing answers fit that bill. So I’ll throw my own hat... You should also note that these water heaters are somewhat dependant on the temperature of the incoming water. If that is really icy, they will struggle to reach the max, without throttling the flow. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 10, 2015, 1:18pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/5 "2015-12-10T13:18:00Z")
You could get a hot water tank to hold the water at a higher temperature, just hot enough that your tankless system has no trouble with the boost, and keeping that water at such a temperature should not cost that much, perhaps even room temperature, would do it, so after the initial heating from outside temp to room temp it requires no additional energy. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 10, 2015, 1:31pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/6 "2015-12-10T13:31:03Z")
As for in series, that would only work if you could lower the temp of the first unit enough so no water throttling occurred, the second unit would do all the throttling. In parallel should double your water flow rate I would guess. I still think the standby hot water tank would be overall cheaper. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [December 10, 2015, 2:03pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/7 "2015-12-10T14:03:52Z")
If you’ve got 80,000 BTU per hour at 10 liters per minute you’ll only get a delta T of 60 degrees F. To reach 140 deg F out you’ll need 80 deg F in, which isn’t happening. If your inlet water is 60 deg F you should be able to make 7.5 liters per minute of 140 deg F water though, are you sure your unit is heating per specifications? ---
**Author:** ![busterpickle](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@busterpickle](https://boards.straightdope.com/u/busterpickle)\ **Post date:** [December 10, 2015, 5:19pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/8 "2015-12-10T17:19:57Z")
From talking to plumbers and the like, tankless never works well by itself, or rather, as advertised. They always recommend hybrid systems: tankless and a small water heater. This reminds me of a lot of things like manufacture stated MPG, HP, UPS run times, etc. It’s always lower, sometimes up to 30%. Yours is really low going from 7.5 LPM to 2 LPM which makes me think what someone else had stated about how well that unit is working. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 10, 2015, 5:32pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/9 "2015-12-10T17:32:22Z")
From what I’ve heard tankless never works well enough to take a shower. Even small tanks do better because you can get the water up to max temperature and then mixed with some cold you’ll get a decent shower. With tankless you’re stuck with whatever heating can be done as the water flows. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [December 10, 2015, 6:31pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/10 "2015-12-10T18:31:42Z")
> [@TriPolar](#): > > From what I’ve heard tankless never works well enough to take a shower. No, this isn’t true. There are some small cheap on-demand water heaters which may not have the capacity, but many of the quality units can and do provide adequate hot water for a shower. I’ve had a low to mid-sized good quality unit for 8 years now, and have to turn on the cold water to mix with the hot when I take a shower (IOW the heater can meet the demand). I’m in Canada and our incoming water gets pretty close to freezing, so the technology definately can work for a shower. Many people who are displeased with tankless are used to having a hot water tank, with which you can open every faucet in the house and get hot water flowing as fast as the incoming pressure can push it (of course this only last a certain number of minutes before all the hot water is gone and then everything turns luke warm). Tankless definately do have a limited total flow capacity, and unless the tankless unit is very large/powerful then a conventional tank will always out-perform tankless in the short-term high volume production of hot water. But most properly sized (and functioning) units can deliver enough hot water for a normal shower. On the “correctly functioning” side, you might want to check the piping scheme inside your tankless heater. My new unit has one big heating area, but my old one ran 2 smaller heating units in parallel which then combined into one hot water outlet. One of those heating units develloped a wiring problem and stopped working, reducing the heating capacity of the heater by half… however the heater looked normal from the outside and all the lights lit up normally. It’s possible you unit could have some sort of electrical defect which limits it’s output; worth checking out before spending money to add to or alter your system. Actually I just realized yours is a gas unit (mine’s electric)… same advice though as it too may have some sort of defect which keeps it from functioning correctly. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [December 10, 2015, 6:41pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/11 "2015-12-10T18:41:27Z")
Another thing to check is the diameter of your incoming gas line. We looked at tankless, and we were lucky enough to have a plumber who pointed out that our incoming line was too small at 1/2", and that to get proper performance, you really need a larger pipe. He recommended that we get a larger and more modern conventional water heater than we’d previously had (I think we went to 60 gallons from 40 gallons). But on other quotes, NOBODY pointed the gas line issue out- they were all too eager to sell us tankless systems. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [December 10, 2015, 6:54pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/12 "2015-12-10T18:54:08Z")
Tankless water heater owner here. I have a whole house system and it adequately puts out enough hot water to shower with while the laundry or dishwasher is in action. It’s also been tested with two simultaneous showers. I’m not at home now so I can’t give you the BTU rating but it is set to output 125 degree water. I’m curious as to why anyone would want 140 degree water since full on 125 degree hot water is damn hot. Hotter than I could stand in a shower. It is NOT a hybrid system. Like any centralized heater it takes a while (20 seconds) for the shower to warm up while the heated water travels from the water heater to the shower head. The biggest disadvantage (not very big at all) is when I jump into the shower five minutes after my wife is finished with hers. There is residual heat in the pipes so the water is instantly warm, just like any central system. But 20 seconds (remember that 20 seconds I mentioned earlier) later there is about two cups of cold water bursting through. This is caused by the fact that some cold water gets through the water heater as it is initializing. You don’t notice it when you’re the first one to shower as its just part of the normal delay. So, even though the temperature may feel inviting, I always give the shower 20 seconds to warm up. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 10, 2015, 7:00pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/13 "2015-12-10T19:00:03Z")
> [@mmmiiikkkeee](#): > > No, this isn’t true. Yes it is true. That’s what I’ve heard. What I’ve heard may not be true. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [December 10, 2015, 7:44pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/14 "2015-12-10T19:44:59Z")
I’m confused; isn’t that what **mmmiiikkkeee** said; that what you heard is not true? I really don’t understand the quibble you have with his/her post. ---
**Author:** ![MindsEye\_Watering](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mindseye_watering/32/3619_2.png) [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)\ **Post date:** [December 10, 2015, 8:26pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/15 "2015-12-10T20:26:26Z")
> [@BubbaDog](#): > > Tankless water heater owner here. > I have a whole house system and it adequately puts out enough hot water to shower with while the laundry or dishwasher is in action. It’s also been tested with two simultaneous showers. > > I’m not at home now so I can’t give you the BTU rating but it is set to output 125 degree water. I’m curious as to why anyone would want 140 degree water since full on 125 degree hot water is damn hot. Hotter than I could stand in a shower. > > It is NOT a hybrid system. Like any centralized heater it takes a while (20 seconds) for the shower to warm up while the heated water travels from the water heater to the shower head. > > The biggest disadvantage (not very big at all) is when I jump into the shower five minutes after my wife is finished with hers. There is residual heat in the pipes so the water is instantly warm, just like any central system. But 20 seconds (remember that 20 seconds I mentioned earlier) later there is about two cups of cold water bursting through. > > This is caused by the fact that some cold water gets through the water heater as it is initializing. You don’t notice it when you’re the first one to shower as its just part of the normal delay. > > So, even though the temperature may feel inviting, I always give the shower 20 seconds to warm up. Same here. More than enough hot water for two showers at the same time. I also have a well with very cold water. My tankless is a Rinnai propane. I’ve heard that _electric_ tankless can be inadequate for anything other than point-of-use. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [December 10, 2015, 11:00pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/16 "2015-12-10T23:00:02Z")
> [@MindsEye\_Watering](#): > > I’ve heard that _electric_ tankless can be inadequate for anything other than point-of-use. Again, not if sized and functioning correctly. My post above is about my experience with electric tankless heaters. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [December 10, 2015, 11:07pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/17 "2015-12-10T23:07:10Z")
In a previous thread, someone said that their electric tankless heater required an 80 or a 100 amp circuit. That’s a lot, given that many homes have only 100 or 200 amps for the whole house. ---
**Author:** ![Terry\_Kennedy](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@Terry\_Kennedy](https://boards.straightdope.com/u/Terry_Kennedy)\ **Post date:** [December 11, 2015, 10:32am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/18 "2015-12-11T10:32:43Z")
> [@BubbaDog](#): > > I’m curious as to why anyone would want 140 degree water since full on 125 degree hot water is damn hot. Hotter than I could stand in a shower. GE [says](http://products.geappliances.com/appliance/gea-specs/GEH50DFEJSR#spec-support): _If more hot water capacity is desired, increasing the temperature from 120º to 135ºF (49º to 57ºC) will enable the same tank of hot water to last about 25% longer because more cold water is mixed in at the shower or faucet._ ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 11, 2015, 11:28am UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/19 "2015-12-11T11:28:35Z")
> [@Terry\_Kennedy](#): > > GE [says](http://products.geappliances.com/appliance/gea-specs/GEH50DFEJSR#spec-support): _If more hot water capacity is desired, increasing the temperature from 120º to 135ºF (49º to 57ºC) will enable the same tank of hot water to last about 25% longer because more cold water is mixed in at the shower or faucet._ But that system is a 50 gallon tank. It is pretty obvious that the hotter the water in a tank is, the less you will need when mixed with cold. It would be interesting to see a response to these comments from the OP. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [December 11, 2015, 2:40pm UTC](https://boards.straightdope.com/t/tankless-hot-water-issue/740057/20 "2015-12-11T14:40:20Z")
The math just doesn’t work. Taking the OP at his word, to heat 2 liters per minute of water to 140 deg F from 32 deg F would only take 28,600 BTU/hr. He supposedly has 80,000 BTU/hr, and you know the inlet isn’t as cold as 32 deg F, so that’s a worst case condition. Where’s the other 50,000 BTU/hr going? Energy doesn’t just disappear, either he’s not getting it or it’s getting out. You’d notice 50,000 BTU/hr coming into your house, that’s like a 15,000 watt heater running. We don’t know if it’s a gas heater or an electric. If it’s gas there might be some energy loss to the exhaust, but it shouldn’t be as much as that. [Next page](https://boards.straightdope.com/t/tankless-hot-water-issue/740057.md?page=2)